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authorjfrijters <jfrijters>2014-11-10 13:00:01 +0300
committerjfrijters <jfrijters>2014-11-10 13:00:01 +0300
commitb5ad4f360d9c86263754dd6391b09da2c4202207 (patch)
tree324d14b0e423f85f62945ae41dfd2b0fb5f61db5
parentb46dcf01d7586e0d28892cb8a5c7ad8366cd39b7 (diff)
Prepare java.util.concurrent.ForkJoinPool for forking.
Diffstat
-rw-r--r--openjdk/allsources.lst2
-rw-r--r--openjdk/java/util/concurrent/ForkJoinPool.java3370
-rw-r--r--openjdk/response.txt1
3 files changed, 3372 insertions, 1 deletions
diff --git a/openjdk/allsources.lst b/openjdk/allsources.lst
index 95bcedca..2bf838b4 100644
--- a/openjdk/allsources.lst
+++ b/openjdk/allsources.lst
@@ -125,6 +125,7 @@ java/net/TwoStacksPlainSocketImpl_c.java
java/nio/Bits.java
java/security/AccessController.java
java/security/ProtectionDomain.java
+java/util/concurrent/ForkJoinPool.java
java/util/concurrent/locks/AbstractQueuedSynchronizer.java
java/util/concurrent/locks/LockSupport.java
java/util/zip/Adler32.java
@@ -10970,7 +10971,6 @@ sun/security/jgss/wrapper/SunNativeProvider.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/ExecutorCompletionService.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/Executors.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/ExecutorService.java
-@OPENJDK@/jdk/src/share/classes/java/util/concurrent/ForkJoinPool.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/ForkJoinTask.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java
@OPENJDK@/jdk/src/share/classes/java/util/concurrent/Future.java
diff --git a/openjdk/java/util/concurrent/ForkJoinPool.java b/openjdk/java/util/concurrent/ForkJoinPool.java
new file mode 100644
index 00000000..9f5e1491
--- /dev/null
+++ b/openjdk/java/util/concurrent/ForkJoinPool.java
@@ -0,0 +1,3370 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+
+import java.lang.Thread.UncaughtExceptionHandler;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.AbstractExecutorService;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+import java.security.AccessControlContext;
+import java.security.ProtectionDomain;
+import java.security.Permissions;
+
+/**
+ * An {@link ExecutorService} for running {@link ForkJoinTask}s.
+ * A {@code ForkJoinPool} provides the entry point for submissions
+ * from non-{@code ForkJoinTask} clients, as well as management and
+ * monitoring operations.
+ *
+ * <p>A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * <em>work-stealing</em>: all threads in the pool attempt to find and
+ * execute tasks submitted to the pool and/or created by other active
+ * tasks (eventually blocking waiting for work if none exist). This
+ * enables efficient processing when most tasks spawn other subtasks
+ * (as do most {@code ForkJoinTask}s), as well as when many small
+ * tasks are submitted to the pool from external clients. Especially
+ * when setting <em>asyncMode</em> to true in constructors, {@code
+ * ForkJoinPool}s may also be appropriate for use with event-style
+ * tasks that are never joined.
+ *
+ * <p>A static {@link #commonPool()} is available and appropriate for
+ * most applications. The common pool is used by any ForkJoinTask that
+ * is not explicitly submitted to a specified pool. Using the common
+ * pool normally reduces resource usage (its threads are slowly
+ * reclaimed during periods of non-use, and reinstated upon subsequent
+ * use).
+ *
+ * <p>For applications that require separate or custom pools, a {@code
+ * ForkJoinPool} may be constructed with a given target parallelism
+ * level; by default, equal to the number of available processors. The
+ * pool attempts to maintain enough active (or available) threads by
+ * dynamically adding, suspending, or resuming internal worker
+ * threads, even if some tasks are stalled waiting to join others.
+ * However, no such adjustments are guaranteed in the face of blocked
+ * I/O or other unmanaged synchronization. The nested {@link
+ * ManagedBlocker} interface enables extension of the kinds of
+ * synchronization accommodated.
+ *
+ * <p>In addition to execution and lifecycle control methods, this
+ * class provides status check methods (for example
+ * {@link #getStealCount}) that are intended to aid in developing,
+ * tuning, and monitoring fork/join applications. Also, method
+ * {@link #toString} returns indications of pool state in a
+ * convenient form for informal monitoring.
+ *
+ * <p>As is the case with other ExecutorServices, there are three
+ * main task execution methods summarized in the following table.
+ * These are designed to be used primarily by clients not already
+ * engaged in fork/join computations in the current pool. The main
+ * forms of these methods accept instances of {@code ForkJoinTask},
+ * but overloaded forms also allow mixed execution of plain {@code
+ * Runnable}- or {@code Callable}- based activities as well. However,
+ * tasks that are already executing in a pool should normally instead
+ * use the within-computation forms listed in the table unless using
+ * async event-style tasks that are not usually joined, in which case
+ * there is little difference among choice of methods.
+ *
+ * <table BORDER CELLPADDING=3 CELLSPACING=1>
+ * <caption>Summary of task execution methods</caption>
+ * <tr>
+ * <td></td>
+ * <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
+ * <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
+ * </tr>
+ * <tr>
+ * <td> <b>Arrange async execution</b></td>
+ * <td> {@link #execute(ForkJoinTask)}</td>
+ * <td> {@link ForkJoinTask#fork}</td>
+ * </tr>
+ * <tr>
+ * <td> <b>Await and obtain result</b></td>
+ * <td> {@link #invoke(ForkJoinTask)}</td>
+ * <td> {@link ForkJoinTask#invoke}</td>
+ * </tr>
+ * <tr>
+ * <td> <b>Arrange exec and obtain Future</b></td>
+ * <td> {@link #submit(ForkJoinTask)}</td>
+ * <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
+ * </tr>
+ * </table>
+ *
+ * <p>The common pool is by default constructed with default
+ * parameters, but these may be controlled by setting three
+ * {@linkplain System#getProperty system properties}:
+ * <ul>
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism}
+ * - the parallelism level, a non-negative integer
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory}
+ * - the class name of a {@link ForkJoinWorkerThreadFactory}
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler}
+ * - the class name of a {@link UncaughtExceptionHandler}
+ * </ul>
+ * If a {@link SecurityManager} is present and no factory is
+ * specified, then the default pool uses a factory supplying
+ * threads that have no {@link Permissions} enabled.
+ * The system class loader is used to load these classes.
+ * Upon any error in establishing these settings, default parameters
+ * are used. It is possible to disable or limit the use of threads in
+ * the common pool by setting the parallelism property to zero, and/or
+ * using a factory that may return {@code null}. However doing so may
+ * cause unjoined tasks to never be executed.
+ *
+ * <p><b>Implementation notes</b>: This implementation restricts the
+ * maximum number of running threads to 32767. Attempts to create
+ * pools with greater than the maximum number result in
+ * {@code IllegalArgumentException}.
+ *
+ * <p>This implementation rejects submitted tasks (that is, by throwing
+ * {@link RejectedExecutionException}) only when the pool is shut down
+ * or internal resources have been exhausted.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+@sun.misc.Contended
+public class ForkJoinPool extends AbstractExecutorService {
+
+ /*
+ * Implementation Overview
+ *
+ * This class and its nested classes provide the main
+ * functionality and control for a set of worker threads:
+ * Submissions from non-FJ threads enter into submission queues.
+ * Workers take these tasks and typically split them into subtasks
+ * that may be stolen by other workers. Preference rules give
+ * first priority to processing tasks from their own queues (LIFO
+ * or FIFO, depending on mode), then to randomized FIFO steals of
+ * tasks in other queues.
+ *
+ * WorkQueues
+ * ==========
+ *
+ * Most operations occur within work-stealing queues (in nested
+ * class WorkQueue). These are special forms of Deques that
+ * support only three of the four possible end-operations -- push,
+ * pop, and poll (aka steal), under the further constraints that
+ * push and pop are called only from the owning thread (or, as
+ * extended here, under a lock), while poll may be called from
+ * other threads. (If you are unfamiliar with them, you probably
+ * want to read Herlihy and Shavit's book "The Art of
+ * Multiprocessor programming", chapter 16 describing these in
+ * more detail before proceeding.) The main work-stealing queue
+ * design is roughly similar to those in the papers "Dynamic
+ * Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
+ * (http://research.sun.com/scalable/pubs/index.html) and
+ * "Idempotent work stealing" by Michael, Saraswat, and Vechev,
+ * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
+ * See also "Correct and Efficient Work-Stealing for Weak Memory
+ * Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
+ * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an
+ * analysis of memory ordering (atomic, volatile etc) issues. The
+ * main differences ultimately stem from GC requirements that we
+ * null out taken slots as soon as we can, to maintain as small a
+ * footprint as possible even in programs generating huge numbers
+ * of tasks. To accomplish this, we shift the CAS arbitrating pop
+ * vs poll (steal) from being on the indices ("base" and "top") to
+ * the slots themselves. So, both a successful pop and poll
+ * mainly entail a CAS of a slot from non-null to null. Because
+ * we rely on CASes of references, we do not need tag bits on base
+ * or top. They are simple ints as used in any circular
+ * array-based queue (see for example ArrayDeque). Updates to the
+ * indices must still be ordered in a way that guarantees that top
+ * == base means the queue is empty, but otherwise may err on the
+ * side of possibly making the queue appear nonempty when a push,
+ * pop, or poll have not fully committed. Note that this means
+ * that the poll operation, considered individually, is not
+ * wait-free. One thief cannot successfully continue until another
+ * in-progress one (or, if previously empty, a push) completes.
+ * However, in the aggregate, we ensure at least probabilistic
+ * non-blockingness. If an attempted steal fails, a thief always
+ * chooses a different random victim target to try next. So, in
+ * order for one thief to progress, it suffices for any
+ * in-progress poll or new push on any empty queue to
+ * complete. (This is why we normally use method pollAt and its
+ * variants that try once at the apparent base index, else
+ * consider alternative actions, rather than method poll.)
+ *
+ * This approach also enables support of a user mode in which local
+ * task processing is in FIFO, not LIFO order, simply by using
+ * poll rather than pop. This can be useful in message-passing
+ * frameworks in which tasks are never joined. However neither
+ * mode considers affinities, loads, cache localities, etc, so
+ * rarely provide the best possible performance on a given
+ * machine, but portably provide good throughput by averaging over
+ * these factors. (Further, even if we did try to use such
+ * information, we do not usually have a basis for exploiting it.
+ * For example, some sets of tasks profit from cache affinities,
+ * but others are harmed by cache pollution effects.)
+ *
+ * WorkQueues are also used in a similar way for tasks submitted
+ * to the pool. We cannot mix these tasks in the same queues used
+ * for work-stealing (this would contaminate lifo/fifo
+ * processing). Instead, we randomly associate submission queues
+ * with submitting threads, using a form of hashing. The
+ * ThreadLocalRandom probe value serves as a hash code for
+ * choosing existing queues, and may be randomly repositioned upon
+ * contention with other submitters. In essence, submitters act
+ * like workers except that they are restricted to executing local
+ * tasks that they submitted (or in the case of CountedCompleters,
+ * others with the same root task). However, because most
+ * shared/external queue operations are more expensive than
+ * internal, and because, at steady state, external submitters
+ * will compete for CPU with workers, ForkJoinTask.join and
+ * related methods disable them from repeatedly helping to process
+ * tasks if all workers are active. Insertion of tasks in shared
+ * mode requires a lock (mainly to protect in the case of
+ * resizing) but we use only a simple spinlock (using bits in
+ * field qlock), because submitters encountering a busy queue move
+ * on to try or create other queues -- they block only when
+ * creating and registering new queues.
+ *
+ * Management
+ * ==========
+ *
+ * The main throughput advantages of work-stealing stem from
+ * decentralized control -- workers mostly take tasks from
+ * themselves or each other. We cannot negate this in the
+ * implementation of other management responsibilities. The main
+ * tactic for avoiding bottlenecks is packing nearly all
+ * essentially atomic control state into two volatile variables
+ * that are by far most often read (not written) as status and
+ * consistency checks.
+ *
+ * Field "ctl" contains 64 bits holding all the information needed
+ * to atomically decide to add, inactivate, enqueue (on an event
+ * queue), dequeue, and/or re-activate workers. To enable this
+ * packing, we restrict maximum parallelism to (1<<15)-1 (which is
+ * far in excess of normal operating range) to allow ids, counts,
+ * and their negations (used for thresholding) to fit into 16bit
+ * fields.
+ *
+ * Field "plock" is a form of sequence lock with a saturating
+ * shutdown bit (similarly for per-queue "qlocks"), mainly
+ * protecting updates to the workQueues array, as well as to
+ * enable shutdown. When used as a lock, it is normally only very
+ * briefly held, so is nearly always available after at most a
+ * brief spin, but we use a monitor-based backup strategy to
+ * block when needed.
+ *
+ * Recording WorkQueues. WorkQueues are recorded in the
+ * "workQueues" array that is created upon first use and expanded
+ * if necessary. Updates to the array while recording new workers
+ * and unrecording terminated ones are protected from each other
+ * by a lock but the array is otherwise concurrently readable, and
+ * accessed directly. To simplify index-based operations, the
+ * array size is always a power of two, and all readers must
+ * tolerate null slots. Worker queues are at odd indices. Shared
+ * (submission) queues are at even indices, up to a maximum of 64
+ * slots, to limit growth even if array needs to expand to add
+ * more workers. Grouping them together in this way simplifies and
+ * speeds up task scanning.
+ *
+ * All worker thread creation is on-demand, triggered by task
+ * submissions, replacement of terminated workers, and/or
+ * compensation for blocked workers. However, all other support
+ * code is set up to work with other policies. To ensure that we
+ * do not hold on to worker references that would prevent GC, ALL
+ * accesses to workQueues are via indices into the workQueues
+ * array (which is one source of some of the messy code
+ * constructions here). In essence, the workQueues array serves as
+ * a weak reference mechanism. Thus for example the wait queue
+ * field of ctl stores indices, not references. Access to the
+ * workQueues in associated methods (for example signalWork) must
+ * both index-check and null-check the IDs. All such accesses
+ * ignore bad IDs by returning out early from what they are doing,
+ * since this can only be associated with termination, in which
+ * case it is OK to give up. All uses of the workQueues array
+ * also check that it is non-null (even if previously
+ * non-null). This allows nulling during termination, which is
+ * currently not necessary, but remains an option for
+ * resource-revocation-based shutdown schemes. It also helps
+ * reduce JIT issuance of uncommon-trap code, which tends to
+ * unnecessarily complicate control flow in some methods.
+ *
+ * Event Queuing. Unlike HPC work-stealing frameworks, we cannot
+ * let workers spin indefinitely scanning for tasks when none can
+ * be found immediately, and we cannot start/resume workers unless
+ * there appear to be tasks available. On the other hand, we must
+ * quickly prod them into action when new tasks are submitted or
+ * generated. In many usages, ramp-up time to activate workers is
+ * the main limiting factor in overall performance (this is
+ * compounded at program start-up by JIT compilation and
+ * allocation). So we try to streamline this as much as possible.
+ * We park/unpark workers after placing in an event wait queue
+ * when they cannot find work. This "queue" is actually a simple
+ * Treiber stack, headed by the "id" field of ctl, plus a 15bit
+ * counter value (that reflects the number of times a worker has
+ * been inactivated) to avoid ABA effects (we need only as many
+ * version numbers as worker threads). Successors are held in
+ * field WorkQueue.nextWait. Queuing deals with several intrinsic
+ * races, mainly that a task-producing thread can miss seeing (and
+ * signalling) another thread that gave up looking for work but
+ * has not yet entered the wait queue. We solve this by requiring
+ * a full sweep of all workers (via repeated calls to method
+ * scan()) both before and after a newly waiting worker is added
+ * to the wait queue. Because enqueued workers may actually be
+ * rescanning rather than waiting, we set and clear the "parker"
+ * field of WorkQueues to reduce unnecessary calls to unpark.
+ * (This requires a secondary recheck to avoid missed signals.)
+ * Note the unusual conventions about Thread.interrupts
+ * surrounding parking and other blocking: Because interrupts are
+ * used solely to alert threads to check termination, which is
+ * checked anyway upon blocking, we clear status (using
+ * Thread.interrupted) before any call to park, so that park does
+ * not immediately return due to status being set via some other
+ * unrelated call to interrupt in user code.
+ *
+ * Signalling. We create or wake up workers only when there
+ * appears to be at least one task they might be able to find and
+ * execute. When a submission is added or another worker adds a
+ * task to a queue that has fewer than two tasks, they signal
+ * waiting workers (or trigger creation of new ones if fewer than
+ * the given parallelism level -- signalWork). These primary
+ * signals are buttressed by others whenever other threads remove
+ * a task from a queue and notice that there are other tasks there
+ * as well. So in general, pools will be over-signalled. On most
+ * platforms, signalling (unpark) overhead time is noticeably
+ * long, and the time between signalling a thread and it actually
+ * making progress can be very noticeably long, so it is worth
+ * offloading these delays from critical paths as much as
+ * possible. Additionally, workers spin-down gradually, by staying
+ * alive so long as they see the ctl state changing. Similar
+ * stability-sensing techniques are also used before blocking in
+ * awaitJoin and helpComplete.
+ *
+ * Trimming workers. To release resources after periods of lack of
+ * use, a worker starting to wait when the pool is quiescent will
+ * time out and terminate if the pool has remained quiescent for a
+ * given period -- a short period if there are more threads than
+ * parallelism, longer as the number of threads decreases. This
+ * will slowly propagate, eventually terminating all workers after
+ * periods of non-use.
+ *
+ * Shutdown and Termination. A call to shutdownNow atomically sets
+ * a plock bit and then (non-atomically) sets each worker's
+ * qlock status, cancels all unprocessed tasks, and wakes up
+ * all waiting workers. Detecting whether termination should
+ * commence after a non-abrupt shutdown() call requires more work
+ * and bookkeeping. We need consensus about quiescence (i.e., that
+ * there is no more work). The active count provides a primary
+ * indication but non-abrupt shutdown still requires a rechecking
+ * scan for any workers that are inactive but not queued.
+ *
+ * Joining Tasks
+ * =============
+ *
+ * Any of several actions may be taken when one worker is waiting
+ * to join a task stolen (or always held) by another. Because we
+ * are multiplexing many tasks on to a pool of workers, we can't
+ * just let them block (as in Thread.join). We also cannot just
+ * reassign the joiner's run-time stack with another and replace
+ * it later, which would be a form of "continuation", that even if
+ * possible is not necessarily a good idea since we sometimes need
+ * both an unblocked task and its continuation to progress.
+ * Instead we combine two tactics:
+ *
+ * Helping: Arranging for the joiner to execute some task that it
+ * would be running if the steal had not occurred.
+ *
+ * Compensating: Unless there are already enough live threads,
+ * method tryCompensate() may create or re-activate a spare
+ * thread to compensate for blocked joiners until they unblock.
+ *
+ * A third form (implemented in tryRemoveAndExec) amounts to
+ * helping a hypothetical compensator: If we can readily tell that
+ * a possible action of a compensator is to steal and execute the
+ * task being joined, the joining thread can do so directly,
+ * without the need for a compensation thread (although at the
+ * expense of larger run-time stacks, but the tradeoff is
+ * typically worthwhile).
+ *
+ * The ManagedBlocker extension API can't use helping so relies
+ * only on compensation in method awaitBlocker.
+ *
+ * The algorithm in tryHelpStealer entails a form of "linear"
+ * helping: Each worker records (in field currentSteal) the most
+ * recent task it stole from some other worker. Plus, it records
+ * (in field currentJoin) the task it is currently actively
+ * joining. Method tryHelpStealer uses these markers to try to
+ * find a worker to help (i.e., steal back a task from and execute
+ * it) that could hasten completion of the actively joined task.
+ * In essence, the joiner executes a task that would be on its own
+ * local deque had the to-be-joined task not been stolen. This may
+ * be seen as a conservative variant of the approach in Wagner &
+ * Calder "Leapfrogging: a portable technique for implementing
+ * efficient futures" SIGPLAN Notices, 1993
+ * (http://portal.acm.org/citation.cfm?id=155354). It differs in
+ * that: (1) We only maintain dependency links across workers upon
+ * steals, rather than use per-task bookkeeping. This sometimes
+ * requires a linear scan of workQueues array to locate stealers,
+ * but often doesn't because stealers leave hints (that may become
+ * stale/wrong) of where to locate them. It is only a hint
+ * because a worker might have had multiple steals and the hint
+ * records only one of them (usually the most current). Hinting
+ * isolates cost to when it is needed, rather than adding to
+ * per-task overhead. (2) It is "shallow", ignoring nesting and
+ * potentially cyclic mutual steals. (3) It is intentionally
+ * racy: field currentJoin is updated only while actively joining,
+ * which means that we miss links in the chain during long-lived
+ * tasks, GC stalls etc (which is OK since blocking in such cases
+ * is usually a good idea). (4) We bound the number of attempts
+ * to find work (see MAX_HELP) and fall back to suspending the
+ * worker and if necessary replacing it with another.
+ *
+ * Helping actions for CountedCompleters are much simpler: Method
+ * helpComplete can take and execute any task with the same root
+ * as the task being waited on. However, this still entails some
+ * traversal of completer chains, so is less efficient than using
+ * CountedCompleters without explicit joins.
+ *
+ * It is impossible to keep exactly the target parallelism number
+ * of threads running at any given time. Determining the
+ * existence of conservatively safe helping targets, the
+ * availability of already-created spares, and the apparent need
+ * to create new spares are all racy, so we rely on multiple
+ * retries of each. Compensation in the apparent absence of
+ * helping opportunities is challenging to control on JVMs, where
+ * GC and other activities can stall progress of tasks that in
+ * turn stall out many other dependent tasks, without us being
+ * able to determine whether they will ever require compensation.
+ * Even though work-stealing otherwise encounters little
+ * degradation in the presence of more threads than cores,
+ * aggressively adding new threads in such cases entails risk of
+ * unwanted positive feedback control loops in which more threads
+ * cause more dependent stalls (as well as delayed progress of
+ * unblocked threads to the point that we know they are available)
+ * leading to more situations requiring more threads, and so
+ * on. This aspect of control can be seen as an (analytically
+ * intractable) game with an opponent that may choose the worst
+ * (for us) active thread to stall at any time. We take several
+ * precautions to bound losses (and thus bound gains), mainly in
+ * methods tryCompensate and awaitJoin.
+ *
+ * Common Pool
+ * ===========
+ *
+ * The static common pool always exists after static
+ * initialization. Since it (or any other created pool) need
+ * never be used, we minimize initial construction overhead and
+ * footprint to the setup of about a dozen fields, with no nested
+ * allocation. Most bootstrapping occurs within method
+ * fullExternalPush during the first submission to the pool.
+ *
+ * When external threads submit to the common pool, they can
+ * perform subtask processing (see externalHelpJoin and related
+ * methods). This caller-helps policy makes it sensible to set
+ * common pool parallelism level to one (or more) less than the
+ * total number of available cores, or even zero for pure
+ * caller-runs. We do not need to record whether external
+ * submissions are to the common pool -- if not, externalHelpJoin
+ * returns quickly (at the most helping to signal some common pool
+ * workers). These submitters would otherwise be blocked waiting
+ * for completion, so the extra effort (with liberally sprinkled
+ * task status checks) in inapplicable cases amounts to an odd
+ * form of limited spin-wait before blocking in ForkJoinTask.join.
+ *
+ * As a more appropriate default in managed environments, unless
+ * overridden by system properties, we use workers of subclass
+ * InnocuousForkJoinWorkerThread when there is a SecurityManager
+ * present. These workers have no permissions set, do not belong
+ * to any user-defined ThreadGroup, and erase all ThreadLocals
+ * after executing any top-level task (see WorkQueue.runTask). The
+ * associated mechanics (mainly in ForkJoinWorkerThread) may be
+ * JVM-dependent and must access particular Thread class fields to
+ * achieve this effect.
+ *
+ * Style notes
+ * ===========
+ *
+ * There is a lot of representation-level coupling among classes
+ * ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask. The
+ * fields of WorkQueue maintain data structures managed by
+ * ForkJoinPool, so are directly accessed. There is little point
+ * trying to reduce this, since any associated future changes in
+ * representations will need to be accompanied by algorithmic
+ * changes anyway. Several methods intrinsically sprawl because
+ * they must accumulate sets of consistent reads of volatiles held
+ * in local variables. Methods signalWork() and scan() are the
+ * main bottlenecks, so are especially heavily
+ * micro-optimized/mangled. There are lots of inline assignments
+ * (of form "while ((local = field) != 0)") which are usually the
+ * simplest way to ensure the required read orderings (which are
+ * sometimes critical). This leads to a "C"-like style of listing
+ * declarations of these locals at the heads of methods or blocks.
+ * There are several occurrences of the unusual "do {} while
+ * (!cas...)" which is the simplest way to force an update of a
+ * CAS'ed variable. There are also other coding oddities (including
+ * several unnecessary-looking hoisted null checks) that help
+ * some methods perform reasonably even when interpreted (not
+ * compiled).
+ *
+ * The order of declarations in this file is:
+ * (1) Static utility functions
+ * (2) Nested (static) classes
+ * (3) Static fields
+ * (4) Fields, along with constants used when unpacking some of them
+ * (5) Internal control methods
+ * (6) Callbacks and other support for ForkJoinTask methods
+ * (7) Exported methods
+ * (8) Static block initializing statics in minimally dependent order
+ */
+
+ // Static utilities
+
+ /**
+ * If there is a security manager, makes sure caller has
+ * permission to modify threads.
+ */
+ private static void checkPermission() {
+ SecurityManager security = System.getSecurityManager();
+ if (security != null)
+ security.checkPermission(modifyThreadPermission);
+ }
+
+ // Nested classes
+
+ /**
+ * Factory for creating new {@link ForkJoinWorkerThread}s.
+ * A {@code ForkJoinWorkerThreadFactory} must be defined and used
+ * for {@code ForkJoinWorkerThread} subclasses that extend base
+ * functionality or initialize threads with different contexts.
+ */
+ public static interface ForkJoinWorkerThreadFactory {
+ /**
+ * Returns a new worker thread operating in the given pool.
+ *
+ * @param pool the pool this thread works in
+ * @return the new worker thread
+ * @throws NullPointerException if the pool is null
+ */
+ public ForkJoinWorkerThread newThread(ForkJoinPool pool);
+ }
+
+ /**
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
+ * new ForkJoinWorkerThread.
+ */
+ static final class DefaultForkJoinWorkerThreadFactory
+ implements ForkJoinWorkerThreadFactory {
+ public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+ return new ForkJoinWorkerThread(pool);
+ }
+ }
+
+ /**
+ * Class for artificial tasks that are used to replace the target
+ * of local joins if they are removed from an interior queue slot
+ * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
+ * actually do anything beyond having a unique identity.
+ */
+ static final class EmptyTask extends ForkJoinTask<Void> {
+ private static final long serialVersionUID = -7721805057305804111L;
+ EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
+ public final Void getRawResult() { return null; }
+ public final void setRawResult(Void x) {}
+ public final boolean exec() { return true; }
+ }
+
+ /**
+ * Queues supporting work-stealing as well as external task
+ * submission. See above for main rationale and algorithms.
+ * Implementation relies heavily on "Unsafe" intrinsics
+ * and selective use of "volatile":
+ *
+ * Field "base" is the index (mod array.length) of the least valid
+ * queue slot, which is always the next position to steal (poll)
+ * from if nonempty. Reads and writes require volatile orderings
+ * but not CAS, because updates are only performed after slot
+ * CASes.
+ *
+ * Field "top" is the index (mod array.length) of the next queue
+ * slot to push to or pop from. It is written only by owner thread
+ * for push, or under lock for external/shared push, and accessed
+ * by other threads only after reading (volatile) base. Both top
+ * and base are allowed to wrap around on overflow, but (top -
+ * base) (or more commonly -(base - top) to force volatile read of
+ * base before top) still estimates size. The lock ("qlock") is
+ * forced to -1 on termination, causing all further lock attempts
+ * to fail. (Note: we don't need CAS for termination state because
+ * upon pool shutdown, all shared-queues will stop being used
+ * anyway.) Nearly all lock bodies are set up so that exceptions
+ * within lock bodies are "impossible" (modulo JVM errors that
+ * would cause failure anyway.)
+ *
+ * The array slots are read and written using the emulation of
+ * volatiles/atomics provided by Unsafe. Insertions must in
+ * general use putOrderedObject as a form of releasing store to
+ * ensure that all writes to the task object are ordered before
+ * its publication in the queue. All removals entail a CAS to
+ * null. The array is always a power of two. To ensure safety of
+ * Unsafe array operations, all accesses perform explicit null
+ * checks and implicit bounds checks via power-of-two masking.
+ *
+ * In addition to basic queuing support, this class contains
+ * fields described elsewhere to control execution. It turns out
+ * to work better memory-layout-wise to include them in this class
+ * rather than a separate class.
+ *
+ * Performance on most platforms is very sensitive to placement of
+ * instances of both WorkQueues and their arrays -- we absolutely
+ * do not want multiple WorkQueue instances or multiple queue
+ * arrays sharing cache lines. (It would be best for queue objects
+ * and their arrays to share, but there is nothing available to
+ * help arrange that). The @Contended annotation alerts JVMs to
+ * try to keep instances apart.
+ */
+ @sun.misc.Contended
+ static final class WorkQueue {
+ /**
+ * Capacity of work-stealing queue array upon initialization.
+ * Must be a power of two; at least 4, but should be larger to
+ * reduce or eliminate cacheline sharing among queues.
+ * Currently, it is much larger, as a partial workaround for
+ * the fact that JVMs often place arrays in locations that
+ * share GC bookkeeping (especially cardmarks) such that
+ * per-write accesses encounter serious memory contention.
+ */
+ static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
+
+ /**
+ * Maximum size for queue arrays. Must be a power of two less
+ * than or equal to 1 << (31 - width of array entry) to ensure
+ * lack of wraparound of index calculations, but defined to a
+ * value a bit less than this to help users trap runaway
+ * programs before saturating systems.
+ */
+ static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
+
+ volatile int eventCount; // encoded inactivation count; < 0 if inactive
+ int nextWait; // encoded record of next event waiter
+ int nsteals; // number of steals
+ int hint; // steal index hint
+ short poolIndex; // index of this queue in pool
+ final short mode; // 0: lifo, > 0: fifo, < 0: shared
+ volatile int qlock; // 1: locked, -1: terminate; else 0
+ volatile int base; // index of next slot for poll
+ int top; // index of next slot for push
+ ForkJoinTask<?>[] array; // the elements (initially unallocated)
+ final ForkJoinPool pool; // the containing pool (may be null)
+ final ForkJoinWorkerThread owner; // owning thread or null if shared
+ volatile Thread parker; // == owner during call to park; else null
+ volatile ForkJoinTask<?> currentJoin; // task being joined in awaitJoin
+ ForkJoinTask<?> currentSteal; // current non-local task being executed
+
+ WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode,
+ int seed) {
+ this.pool = pool;
+ this.owner = owner;
+ this.mode = (short)mode;
+ this.hint = seed; // store initial seed for runWorker
+ // Place indices in the center of array (that is not yet allocated)
+ base = top = INITIAL_QUEUE_CAPACITY >>> 1;
+ }
+
+ /**
+ * Returns the approximate number of tasks in the queue.
+ */
+ final int queueSize() {
+ int n = base - top; // non-owner callers must read base first
+ return (n >= 0) ? 0 : -n; // ignore transient negative
+ }
+
+ /**
+ * Provides a more accurate estimate of whether this queue has
+ * any tasks than does queueSize, by checking whether a
+ * near-empty queue has at least one unclaimed task.
+ */
+ final boolean isEmpty() {
+ ForkJoinTask<?>[] a; int m, s;
+ int n = base - (s = top);
+ return (n >= 0 ||
+ (n == -1 &&
+ ((a = array) == null ||
+ (m = a.length - 1) < 0 ||
+ U.getObject
+ (a, (long)((m & (s - 1)) << ASHIFT) + ABASE) == null)));
+ }
+
+ /**
+ * Pushes a task. Call only by owner in unshared queues. (The
+ * shared-queue version is embedded in method externalPush.)
+ *
+ * @param task the task. Caller must ensure non-null.
+ * @throws RejectedExecutionException if array cannot be resized
+ */
+ final void push(ForkJoinTask<?> task) {
+ ForkJoinTask<?>[] a; ForkJoinPool p;
+ int s = top, n;
+ if ((a = array) != null) { // ignore if queue removed
+ int m = a.length - 1;
+ U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task);
+ if ((n = (top = s + 1) - base) <= 2)
+ (p = pool).signalWork(p.workQueues, this);
+ else if (n >= m)
+ growArray();
+ }
+ }
+
+ /**
+ * Initializes or doubles the capacity of array. Call either
+ * by owner or with lock held -- it is OK for base, but not
+ * top, to move while resizings are in progress.
+ */
+ final ForkJoinTask<?>[] growArray() {
+ ForkJoinTask<?>[] oldA = array;
+ int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
+ if (size > MAXIMUM_QUEUE_CAPACITY)
+ throw new RejectedExecutionException("Queue capacity exceeded");
+ int oldMask, t, b;
+ ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size];
+ if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
+ (t = top) - (b = base) > 0) {
+ int mask = size - 1;
+ do {
+ ForkJoinTask<?> x;
+ int oldj = ((b & oldMask) << ASHIFT) + ABASE;
+ int j = ((b & mask) << ASHIFT) + ABASE;
+ x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj);
+ if (x != null &&
+ U.compareAndSwapObject(oldA, oldj, x, null))
+ U.putObjectVolatile(a, j, x);
+ } while (++b != t);
+ }
+ return a;
+ }
+
+ /**
+ * Takes next task, if one exists, in LIFO order. Call only
+ * by owner in unshared queues.
+ */
+ final ForkJoinTask<?> pop() {
+ ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
+ if ((a = array) != null && (m = a.length - 1) >= 0) {
+ for (int s; (s = top - 1) - base >= 0;) {
+ long j = ((m & s) << ASHIFT) + ABASE;
+ if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
+ break;
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s;
+ return t;
+ }
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Takes a task in FIFO order if b is base of queue and a task
+ * can be claimed without contention. Specialized versions
+ * appear in ForkJoinPool methods scan and tryHelpStealer.
+ */
+ final ForkJoinTask<?> pollAt(int b) {
+ ForkJoinTask<?> t; ForkJoinTask<?>[] a;
+ if ((a = array) != null) {
+ int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
+ base == b && U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
+ return t;
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Takes next task, if one exists, in FIFO order.
+ */
+ final ForkJoinTask<?> poll() {
+ ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
+ while ((b = base) - top < 0 && (a = array) != null) {
+ int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+ if (t != null) {
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
+ return t;
+ }
+ }
+ else if (base == b) {
+ if (b + 1 == top)
+ break;
+ Thread.yield(); // wait for lagging update (very rare)
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Takes next task, if one exists, in order specified by mode.
+ */
+ final ForkJoinTask<?> nextLocalTask() {
+ return mode == 0 ? pop() : poll();
+ }
+
+ /**
+ * Returns next task, if one exists, in order specified by mode.
+ */
+ final ForkJoinTask<?> peek() {
+ ForkJoinTask<?>[] a = array; int m;
+ if (a == null || (m = a.length - 1) < 0)
+ return null;
+ int i = mode == 0 ? top - 1 : base;
+ int j = ((i & m) << ASHIFT) + ABASE;
+ return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+ }
+
+ /**
+ * Pops the given task only if it is at the current top.
+ * (A shared version is available only via FJP.tryExternalUnpush)
+ */
+ final boolean tryUnpush(ForkJoinTask<?> t) {
+ ForkJoinTask<?>[] a; int s;
+ if ((a = array) != null && (s = top) != base &&
+ U.compareAndSwapObject
+ (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
+ top = s;
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Removes and cancels all known tasks, ignoring any exceptions.
+ */
+ final void cancelAll() {
+ ForkJoinTask.cancelIgnoringExceptions(currentJoin);
+ ForkJoinTask.cancelIgnoringExceptions(currentSteal);
+ for (ForkJoinTask<?> t; (t = poll()) != null; )
+ ForkJoinTask.cancelIgnoringExceptions(t);
+ }
+
+ // Specialized execution methods
+
+ /**
+ * Polls and runs tasks until empty.
+ */
+ final void pollAndExecAll() {
+ for (ForkJoinTask<?> t; (t = poll()) != null;)
+ t.doExec();
+ }
+
+ /**
+ * Executes a top-level task and any local tasks remaining
+ * after execution.
+ */
+ final void runTask(ForkJoinTask<?> task) {
+ if ((currentSteal = task) != null) {
+ ForkJoinWorkerThread thread;
+ task.doExec();
+ ForkJoinTask<?>[] a = array;
+ int md = mode;
+ ++nsteals;
+ currentSteal = null;
+ if (md != 0)
+ pollAndExecAll();
+ else if (a != null) {
+ int s, m = a.length - 1;
+ ForkJoinTask<?> t;
+ while ((s = top - 1) - base >= 0 &&
+ (t = (ForkJoinTask<?>)U.getAndSetObject
+ (a, ((m & s) << ASHIFT) + ABASE, null)) != null) {
+ top = s;
+ t.doExec();
+ }
+ }
+ if ((thread = owner) != null) // no need to do in finally clause
+ thread.afterTopLevelExec();
+ }
+ }
+
+ /**
+ * If present, removes from queue and executes the given task,
+ * or any other cancelled task. Returns (true) on any CAS
+ * or consistency check failure so caller can retry.
+ *
+ * @return false if no progress can be made, else true
+ */
+ final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
+ boolean stat;
+ ForkJoinTask<?>[] a; int m, s, b, n;
+ if (task != null && (a = array) != null && (m = a.length - 1) >= 0 &&
+ (n = (s = top) - (b = base)) > 0) {
+ boolean removed = false, empty = true;
+ stat = true;
+ for (ForkJoinTask<?> t;;) { // traverse from s to b
+ long j = ((--s & m) << ASHIFT) + ABASE;
+ t = (ForkJoinTask<?>)U.getObject(a, j);
+ if (t == null) // inconsistent length
+ break;
+ else if (t == task) {
+ if (s + 1 == top) { // pop
+ if (!U.compareAndSwapObject(a, j, task, null))
+ break;
+ top = s;
+ removed = true;
+ }
+ else if (base == b) // replace with proxy
+ removed = U.compareAndSwapObject(a, j, task,
+ new EmptyTask());
+ break;
+ }
+ else if (t.status >= 0)
+ empty = false;
+ else if (s + 1 == top) { // pop and throw away
+ if (U.compareAndSwapObject(a, j, t, null))
+ top = s;
+ break;
+ }
+ if (--n == 0) {
+ if (!empty && base == b)
+ stat = false;
+ break;
+ }
+ }
+ if (removed)
+ task.doExec();
+ }
+ else
+ stat = false;
+ return stat;
+ }
+
+ /**
+ * Tries to poll for and execute the given task or any other
+ * task in its CountedCompleter computation.
+ */
+ final boolean pollAndExecCC(CountedCompleter<?> root) {
+ ForkJoinTask<?>[] a; int b; Object o; CountedCompleter<?> t, r;
+ if ((b = base) - top < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ if ((o = U.getObjectVolatile(a, j)) == null)
+ return true; // retry
+ if (o instanceof CountedCompleter) {
+ for (t = (CountedCompleter<?>)o, r = t;;) {
+ if (r == root) {
+ if (base == b &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ U.putOrderedInt(this, QBASE, b + 1);
+ t.doExec();
+ }
+ return true;
+ }
+ else if ((r = r.completer) == null)
+ break; // not part of root computation
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Tries to pop and execute the given task or any other task
+ * in its CountedCompleter computation.
+ */
+ final boolean externalPopAndExecCC(CountedCompleter<?> root) {
+ ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
+ if (base - (s = top) < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+ for (t = (CountedCompleter<?>)o, r = t;;) {
+ if (r == root) {
+ if (U.compareAndSwapInt(this, QLOCK, 0, 1)) {
+ if (top == s && array == a &&
+ U.compareAndSwapObject(a, j, t, null)) {
+ top = s - 1;
+ qlock = 0;
+ t.doExec();
+ }
+ else
+ qlock = 0;
+ }
+ return true;
+ }
+ else if ((r = r.completer) == null)
+ break;
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Internal version
+ */
+ final boolean internalPopAndExecCC(CountedCompleter<?> root) {
+ ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
+ if (base - (s = top) < 0 && (a = array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+ for (t = (CountedCompleter<?>)o, r = t;;) {
+ if (r == root) {
+ if (U.compareAndSwapObject(a, j, t, null)) {
+ top = s - 1;
+ t.doExec();
+ }
+ return true;
+ }
+ else if ((r = r.completer) == null)
+ break;
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Returns true if owned and not known to be blocked.
+ */
+ final boolean isApparentlyUnblocked() {
+ Thread wt; Thread.State s;
+ return (eventCount >= 0 &&
+ (wt = owner) != null &&
+ (s = wt.getState()) != Thread.State.BLOCKED &&
+ s != Thread.State.WAITING &&
+ s != Thread.State.TIMED_WAITING);
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe U;
+ private static final long QBASE;
+ private static final long QLOCK;
+ private static final int ABASE;
+ private static final int ASHIFT;
+ static {
+ try {
+ U = sun.misc.Unsafe.getUnsafe();
+ Class<?> k = WorkQueue.class;
+ Class<?> ak = ForkJoinTask[].class;
+ QBASE = U.objectFieldOffset
+ (k.getDeclaredField("base"));
+ QLOCK = U.objectFieldOffset
+ (k.getDeclaredField("qlock"));
+ ABASE = U.arrayBaseOffset(ak);
+ int scale = U.arrayIndexScale(ak);
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ }
+ }
+
+ // static fields (initialized in static initializer below)
+
+ /**
+ * Creates a new ForkJoinWorkerThread. This factory is used unless
+ * overridden in ForkJoinPool constructors.
+ */
+ public static final ForkJoinWorkerThreadFactory
+ defaultForkJoinWorkerThreadFactory;
+
+ /**
+ * Permission required for callers of methods that may start or
+ * kill threads.
+ */
+ private static final RuntimePermission modifyThreadPermission;
+
+ /**
+ * Common (static) pool. Non-null for public use unless a static
+ * construction exception, but internal usages null-check on use
+ * to paranoically avoid potential initialization circularities
+ * as well as to simplify generated code.
+ */
+ static final ForkJoinPool common;
+
+ /**
+ * Common pool parallelism. To allow simpler use and management
+ * when common pool threads are disabled, we allow the underlying
+ * common.parallelism field to be zero, but in that case still report
+ * parallelism as 1 to reflect resulting caller-runs mechanics.
+ */
+ static final int commonParallelism;
+
+ /**
+ * Sequence number for creating workerNamePrefix.
+ */
+ private static int poolNumberSequence;
+
+ /**
+ * Returns the next sequence number. We don't expect this to
+ * ever contend, so use simple builtin sync.
+ */
+ private static final synchronized int nextPoolId() {
+ return ++poolNumberSequence;
+ }
+
+ // static constants
+
+ /**
+ * Initial timeout value (in nanoseconds) for the thread
+ * triggering quiescence to park waiting for new work. On timeout,
+ * the thread will instead try to shrink the number of
+ * workers. The value should be large enough to avoid overly
+ * aggressive shrinkage during most transient stalls (long GCs
+ * etc).
+ */
+ private static final long IDLE_TIMEOUT = 2000L * 1000L * 1000L; // 2sec
+
+ /**
+ * Timeout value when there are more threads than parallelism level
+ */
+ private static final long FAST_IDLE_TIMEOUT = 200L * 1000L * 1000L;
+
+ /**
+ * Tolerance for idle timeouts, to cope with timer undershoots
+ */
+ private static final long TIMEOUT_SLOP = 2000000L;
+
+ /**
+ * The maximum stolen->joining link depth allowed in method
+ * tryHelpStealer. Must be a power of two. Depths for legitimate
+ * chains are unbounded, but we use a fixed constant to avoid
+ * (otherwise unchecked) cycles and to bound staleness of
+ * traversal parameters at the expense of sometimes blocking when
+ * we could be helping.
+ */
+ private static final int MAX_HELP = 64;
+
+ /**
+ * Increment for seed generators. See class ThreadLocal for
+ * explanation.
+ */
+ private static final int SEED_INCREMENT = 0x9e3779b9;
+
+ /*
+ * Bits and masks for control variables
+ *
+ * Field ctl is a long packed with:
+ * AC: Number of active running workers minus target parallelism (16 bits)
+ * TC: Number of total workers minus target parallelism (16 bits)
+ * ST: true if pool is terminating (1 bit)
+ * EC: the wait count of top waiting thread (15 bits)
+ * ID: poolIndex of top of Treiber stack of waiters (16 bits)
+ *
+ * When convenient, we can extract the upper 32 bits of counts and
+ * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
+ * (int)ctl. The ec field is never accessed alone, but always
+ * together with id and st. The offsets of counts by the target
+ * parallelism and the positionings of fields makes it possible to
+ * perform the most common checks via sign tests of fields: When
+ * ac is negative, there are not enough active workers, when tc is
+ * negative, there are not enough total workers, and when e is
+ * negative, the pool is terminating. To deal with these possibly
+ * negative fields, we use casts in and out of "short" and/or
+ * signed shifts to maintain signedness.
+ *
+ * When a thread is queued (inactivated), its eventCount field is
+ * set negative, which is the only way to tell if a worker is
+ * prevented from executing tasks, even though it must continue to
+ * scan for them to avoid queuing races. Note however that
+ * eventCount updates lag releases so usage requires care.
+ *
+ * Field plock is an int packed with:
+ * SHUTDOWN: true if shutdown is enabled (1 bit)
+ * SEQ: a sequence lock, with PL_LOCK bit set if locked (30 bits)
+ * SIGNAL: set when threads may be waiting on the lock (1 bit)
+ *
+ * The sequence number enables simple consistency checks:
+ * Staleness of read-only operations on the workQueues array can
+ * be checked by comparing plock before vs after the reads.
+ */
+
+ // bit positions/shifts for fields
+ private static final int AC_SHIFT = 48;
+ private static final int TC_SHIFT = 32;
+ private static final int ST_SHIFT = 31;
+ private static final int EC_SHIFT = 16;
+
+ // bounds
+ private static final int SMASK = 0xffff; // short bits
+ private static final int MAX_CAP = 0x7fff; // max #workers - 1
+ private static final int EVENMASK = 0xfffe; // even short bits
+ private static final int SQMASK = 0x007e; // max 64 (even) slots
+ private static final int SHORT_SIGN = 1 << 15;
+ private static final int INT_SIGN = 1 << 31;
+
+ // masks
+ private static final long STOP_BIT = 0x0001L << ST_SHIFT;
+ private static final long AC_MASK = ((long)SMASK) << AC_SHIFT;
+ private static final long TC_MASK = ((long)SMASK) << TC_SHIFT;
+
+ // units for incrementing and decrementing
+ private static final long TC_UNIT = 1L << TC_SHIFT;
+ private static final long AC_UNIT = 1L << AC_SHIFT;
+
+ // masks and units for dealing with u = (int)(ctl >>> 32)
+ private static final int UAC_SHIFT = AC_SHIFT - 32;
+ private static final int UTC_SHIFT = TC_SHIFT - 32;
+ private static final int UAC_MASK = SMASK << UAC_SHIFT;
+ private static final int UTC_MASK = SMASK << UTC_SHIFT;
+ private static final int UAC_UNIT = 1 << UAC_SHIFT;
+ private static final int UTC_UNIT = 1 << UTC_SHIFT;
+
+ // masks and units for dealing with e = (int)ctl
+ private static final int E_MASK = 0x7fffffff; // no STOP_BIT
+ private static final int E_SEQ = 1 << EC_SHIFT;
+
+ // plock bits
+ private static final int SHUTDOWN = 1 << 31;
+ private static final int PL_LOCK = 2;
+ private static final int PL_SIGNAL = 1;
+ private static final int PL_SPINS = 1 << 8;
+
+ // access mode for WorkQueue
+ static final int LIFO_QUEUE = 0;
+ static final int FIFO_QUEUE = 1;
+ static final int SHARED_QUEUE = -1;
+
+ // Instance fields
+ volatile long stealCount; // collects worker counts
+ volatile long ctl; // main pool control
+ volatile int plock; // shutdown status and seqLock
+ volatile int indexSeed; // worker/submitter index seed
+ final short parallelism; // parallelism level
+ final short mode; // LIFO/FIFO
+ WorkQueue[] workQueues; // main registry
+ final ForkJoinWorkerThreadFactory factory;
+ final UncaughtExceptionHandler ueh; // per-worker UEH
+ final String workerNamePrefix; // to create worker name string
+
+ /**
+ * Acquires the plock lock to protect worker array and related
+ * updates. This method is called only if an initial CAS on plock
+ * fails. This acts as a spinlock for normal cases, but falls back
+ * to builtin monitor to block when (rarely) needed. This would be
+ * a terrible idea for a highly contended lock, but works fine as
+ * a more conservative alternative to a pure spinlock.
+ */
+ private int acquirePlock() {
+ int spins = PL_SPINS, ps, nps;
+ for (;;) {
+ if (((ps = plock) & PL_LOCK) == 0 &&
+ U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
+ return nps;
+ else if (spins >= 0) {
+ if (ThreadLocalRandom.nextSecondarySeed() >= 0)
+ --spins;
+ }
+ else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
+ synchronized (this) {
+ if ((plock & PL_SIGNAL) != 0) {
+ try {
+ wait();
+ } catch (InterruptedException ie) {
+ try {
+ Thread.currentThread().interrupt();
+ } catch (SecurityException ignore) {
+ }
+ }
+ }
+ else
+ notifyAll();
+ }
+ }
+ }
+ }
+
+ /**
+ * Unlocks and signals any thread waiting for plock. Called only
+ * when CAS of seq value for unlock fails.
+ */
+ private void releasePlock(int ps) {
+ plock = ps;
+ synchronized (this) { notifyAll(); }
+ }
+
+ /**
+ * Tries to create and start one worker if fewer than target
+ * parallelism level exist. Adjusts counts etc on failure.
+ */
+ private void tryAddWorker() {
+ long c; int u, e;
+ while ((u = (int)((c = ctl) >>> 32)) < 0 &&
+ (u & SHORT_SIGN) != 0 && (e = (int)c) >= 0) {
+ long nc = ((long)(((u + UTC_UNIT) & UTC_MASK) |
+ ((u + UAC_UNIT) & UAC_MASK)) << 32) | (long)e;
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ ForkJoinWorkerThreadFactory fac;
+ Throwable ex = null;
+ ForkJoinWorkerThread wt = null;
+ try {
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
+ break;
+ }
+ } catch (Throwable rex) {
+ ex = rex;
+ }
+ deregisterWorker(wt, ex);
+ break;
+ }
+ }
+ }
+
+ // Registering and deregistering workers
+
+ /**
+ * Callback from ForkJoinWorkerThread to establish and record its
+ * WorkQueue. To avoid scanning bias due to packing entries in
+ * front of the workQueues array, we treat the array as a simple
+ * power-of-two hash table using per-thread seed as hash,
+ * expanding as needed.
+ *
+ * @param wt the worker thread
+ * @return the worker's queue
+ */
+ final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
+ UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
+ wt.setDaemon(true);
+ if ((handler = ueh) != null)
+ wt.setUncaughtExceptionHandler(handler);
+ do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed,
+ s += SEED_INCREMENT) ||
+ s == 0); // skip 0
+ WorkQueue w = new WorkQueue(this, wt, mode, s);
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ try {
+ if ((ws = workQueues) != null) { // skip if shutting down
+ int n = ws.length, m = n - 1;
+ int r = (s << 1) | 1; // use odd-numbered indices
+ if (ws[r &= m] != null) { // collision
+ int probes = 0; // step by approx half size
+ int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2;
+ while (ws[r = (r + step) & m] != null) {
+ if (++probes >= n) {
+ workQueues = ws = Arrays.copyOf(ws, n <<= 1);
+ m = n - 1;
+ probes = 0;
+ }
+ }
+ }
+ w.poolIndex = (short)r;
+ w.eventCount = r; // volatile write orders
+ ws[r] = w;
+ }
+ } finally {
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex >>> 1)));
+ return w;
+ }
+
+ /**
+ * Final callback from terminating worker, as well as upon failure
+ * to construct or start a worker. Removes record of worker from
+ * array, and adjusts counts. If pool is shutting down, tries to
+ * complete termination.
+ *
+ * @param wt the worker thread, or null if construction failed
+ * @param ex the exception causing failure, or null if none
+ */
+ final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
+ WorkQueue w = null;
+ if (wt != null && (w = wt.workQueue) != null) {
+ int ps;
+ w.qlock = -1; // ensure set
+ U.getAndAddLong(this, STEALCOUNT, w.nsteals); // collect steals
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ try {
+ int idx = w.poolIndex;
+ WorkQueue[] ws = workQueues;
+ if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
+ ws[idx] = null;
+ } finally {
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ }
+
+ long c; // adjust ctl counts
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
+ ((c - TC_UNIT) & TC_MASK) |
+ (c & ~(AC_MASK|TC_MASK)))));
+
+ if (!tryTerminate(false, false) && w != null && w.array != null) {
+ w.cancelAll(); // cancel remaining tasks
+ WorkQueue[] ws; WorkQueue v; Thread p; int u, i, e;
+ while ((u = (int)((c = ctl) >>> 32)) < 0 && (e = (int)c) >= 0) {
+ if (e > 0) { // activate or create replacement
+ if ((ws = workQueues) == null ||
+ (i = e & SMASK) >= ws.length ||
+ (v = ws[i]) == null)
+ break;
+ long nc = (((long)(v.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT) << 32));
+ if (v.eventCount != (e | INT_SIGN))
+ break;
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = (e + E_SEQ) & E_MASK;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ break;
+ }
+ }
+ else {
+ if ((short)u < 0)
+ tryAddWorker();
+ break;
+ }
+ }
+ }
+ if (ex == null) // help clean refs on way out
+ ForkJoinTask.helpExpungeStaleExceptions();
+ else // rethrow
+ ForkJoinTask.rethrow(ex);
+ }
+
+ // Submissions
+
+ /**
+ * Unless shutting down, adds the given task to a submission queue
+ * at submitter's current queue index (modulo submission
+ * range). Only the most common path is directly handled in this
+ * method. All others are relayed to fullExternalPush.
+ *
+ * @param task the task. Caller must ensure non-null.
+ */
+ final void externalPush(ForkJoinTask<?> task) {
+ WorkQueue q; int m, s, n, am; ForkJoinTask<?>[] a;
+ int r = ThreadLocalRandom.getProbe();
+ int ps = plock;
+ WorkQueue[] ws = workQueues;
+ if (ps > 0 && ws != null && (m = (ws.length - 1)) >= 0 &&
+ (q = ws[m & r & SQMASK]) != null && r != 0 &&
+ U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
+ if ((a = q.array) != null &&
+ (am = a.length - 1) > (n = (s = q.top) - q.base)) {
+ int j = ((am & s) << ASHIFT) + ABASE;
+ U.putOrderedObject(a, j, task);
+ q.top = s + 1; // push on to deque
+ q.qlock = 0;
+ if (n <= 1)
+ signalWork(ws, q);
+ return;
+ }
+ q.qlock = 0;
+ }
+ fullExternalPush(task);
+ }
+
+ /**
+ * Full version of externalPush. This method is called, among
+ * other times, upon the first submission of the first task to the
+ * pool, so must perform secondary initialization. It also
+ * detects first submission by an external thread by looking up
+ * its ThreadLocal, and creates a new shared queue if the one at
+ * index if empty or contended. The plock lock body must be
+ * exception-free (so no try/finally) so we optimistically
+ * allocate new queues outside the lock and throw them away if
+ * (very rarely) not needed.
+ *
+ * Secondary initialization occurs when plock is zero, to create
+ * workQueue array and set plock to a valid value. This lock body
+ * must also be exception-free. Because the plock seq value can
+ * eventually wrap around zero, this method harmlessly fails to
+ * reinitialize if workQueues exists, while still advancing plock.
+ */
+ private void fullExternalPush(ForkJoinTask<?> task) {
+ int r;
+ if ((r = ThreadLocalRandom.getProbe()) == 0) {
+ ThreadLocalRandom.localInit();
+ r = ThreadLocalRandom.getProbe();
+ }
+ for (;;) {
+ WorkQueue[] ws; WorkQueue q; int ps, m, k;
+ boolean move = false;
+ if ((ps = plock) < 0)
+ throw new RejectedExecutionException();
+ else if (ps == 0 || (ws = workQueues) == null ||
+ (m = ws.length - 1) < 0) { // initialize workQueues
+ int p = parallelism; // find power of two table size
+ int n = (p > 1) ? p - 1 : 1; // ensure at least 2 slots
+ n |= n >>> 1; n |= n >>> 2; n |= n >>> 4;
+ n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1;
+ WorkQueue[] nws = ((ws = workQueues) == null || ws.length == 0 ?
+ new WorkQueue[n] : null);
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if (((ws = workQueues) == null || ws.length == 0) && nws != null)
+ workQueues = nws;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ else if ((q = ws[k = r & m & SQMASK]) != null) {
+ if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
+ ForkJoinTask<?>[] a = q.array;
+ int s = q.top;
+ boolean submitted = false;
+ try { // locked version of push
+ if ((a != null && a.length > s + 1 - q.base) ||
+ (a = q.growArray()) != null) { // must presize
+ int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
+ U.putOrderedObject(a, j, task);
+ q.top = s + 1;
+ submitted = true;
+ }
+ } finally {
+ q.qlock = 0; // unlock
+ }
+ if (submitted) {
+ signalWork(ws, q);
+ return;
+ }
+ }
+ move = true; // move on failure
+ }
+ else if (((ps = plock) & PL_LOCK) == 0) { // create new queue
+ q = new WorkQueue(this, null, SHARED_QUEUE, r);
+ q.poolIndex = (short)k;
+ if (((ps = plock) & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ if ((ws = workQueues) != null && k < ws.length && ws[k] == null)
+ ws[k] = q;
+ int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ else
+ move = true; // move if busy
+ if (move)
+ r = ThreadLocalRandom.advanceProbe(r);
+ }
+ }
+
+ // Maintaining ctl counts
+
+ /**
+ * Increments active count; mainly called upon return from blocking.
+ */
+ final void incrementActiveCount() {
+ long c;
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl, ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
+ }
+
+ /**
+ * Tries to create or activate a worker if too few are active.
+ *
+ * @param ws the worker array to use to find signallees
+ * @param q if non-null, the queue holding tasks to be processed
+ */
+ final void signalWork(WorkQueue[] ws, WorkQueue q) {
+ for (;;) {
+ long c; int e, u, i; WorkQueue w; Thread p;
+ if ((u = (int)((c = ctl) >>> 32)) >= 0)
+ break;
+ if ((e = (int)c) <= 0) {
+ if ((short)u < 0)
+ tryAddWorker();
+ break;
+ }
+ if (ws == null || ws.length <= (i = e & SMASK) ||
+ (w = ws[i]) == null)
+ break;
+ long nc = (((long)(w.nextWait & E_MASK)) |
+ ((long)(u + UAC_UNIT)) << 32);
+ int ne = (e + E_SEQ) & E_MASK;
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = ne;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ break;
+ }
+ if (q != null && q.base >= q.top)
+ break;
+ }
+ }
+
+ // Scanning for tasks
+
+ /**
+ * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
+ */
+ final void runWorker(WorkQueue w) {
+ w.growArray(); // allocate queue
+ for (int r = w.hint; scan(w, r) == 0; ) {
+ r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
+ }
+ }
+
+ /**
+ * Scans for and, if found, runs one task, else possibly
+ * inactivates the worker. This method operates on single reads of
+ * volatile state and is designed to be re-invoked continuously,
+ * in part because it returns upon detecting inconsistencies,
+ * contention, or state changes that indicate possible success on
+ * re-invocation.
+ *
+ * The scan searches for tasks across queues starting at a random
+ * index, checking each at least twice. The scan terminates upon
+ * either finding a non-empty queue, or completing the sweep. If
+ * the worker is not inactivated, it takes and runs a task from
+ * this queue. Otherwise, if not activated, it tries to activate
+ * itself or some other worker by signalling. On failure to find a
+ * task, returns (for retry) if pool state may have changed during
+ * an empty scan, or tries to inactivate if active, else possibly
+ * blocks or terminates via method awaitWork.
+ *
+ * @param w the worker (via its WorkQueue)
+ * @param r a random seed
+ * @return worker qlock status if would have waited, else 0
+ */
+ private final int scan(WorkQueue w, int r) {
+ WorkQueue[] ws; int m;
+ long c = ctl; // for consistency check
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && w != null) {
+ for (int j = m + m + 1, ec = w.eventCount;;) {
+ WorkQueue q; int b, e; ForkJoinTask<?>[] a; ForkJoinTask<?> t;
+ if ((q = ws[(r - j) & m]) != null &&
+ (b = q.base) - q.top < 0 && (a = q.array) != null) {
+ long i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ if ((t = ((ForkJoinTask<?>)
+ U.getObjectVolatile(a, i))) != null) {
+ if (ec < 0)
+ helpRelease(c, ws, w, q, b);
+ else if (q.base == b &&
+ U.compareAndSwapObject(a, i, t, null)) {
+ U.putOrderedInt(q, QBASE, b + 1);
+ if ((b + 1) - q.top < 0)
+ signalWork(ws, q);
+ w.runTask(t);
+ }
+ }
+ break;
+ }
+ else if (--j < 0) {
+ if ((ec | (e = (int)c)) < 0) // inactive or terminating
+ return awaitWork(w, c, ec);
+ else if (ctl == c) { // try to inactivate and enqueue
+ long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+ w.nextWait = e;
+ w.eventCount = ec | INT_SIGN;
+ if (!U.compareAndSwapLong(this, CTL, c, nc))
+ w.eventCount = ec; // back out
+ }
+ break;
+ }
+ }
+ }
+ return 0;
+ }
+
+ /**
+ * A continuation of scan(), possibly blocking or terminating
+ * worker w. Returns without blocking if pool state has apparently
+ * changed since last invocation. Also, if inactivating w has
+ * caused the pool to become quiescent, checks for pool
+ * termination, and, so long as this is not the only worker, waits
+ * for event for up to a given duration. On timeout, if ctl has
+ * not changed, terminates the worker, which will in turn wake up
+ * another worker to possibly repeat this process.
+ *
+ * @param w the calling worker
+ * @param c the ctl value on entry to scan
+ * @param ec the worker's eventCount on entry to scan
+ */
+ private final int awaitWork(WorkQueue w, long c, int ec) {
+ int stat, ns; long parkTime, deadline;
+ if ((stat = w.qlock) >= 0 && w.eventCount == ec && ctl == c &&
+ !Thread.interrupted()) {
+ int e = (int)c;
+ int u = (int)(c >>> 32);
+ int d = (u >> UAC_SHIFT) + parallelism; // active count
+
+ if (e < 0 || (d <= 0 && tryTerminate(false, false)))
+ stat = w.qlock = -1; // pool is terminating
+ else if ((ns = w.nsteals) != 0) { // collect steals and retry
+ w.nsteals = 0;
+ U.getAndAddLong(this, STEALCOUNT, (long)ns);
+ }
+ else {
+ long pc = ((d > 0 || ec != (e | INT_SIGN)) ? 0L :
+ ((long)(w.nextWait & E_MASK)) | // ctl to restore
+ ((long)(u + UAC_UNIT)) << 32);
+ if (pc != 0L) { // timed wait if last waiter
+ int dc = -(short)(c >>> TC_SHIFT);
+ parkTime = (dc < 0 ? FAST_IDLE_TIMEOUT:
+ (dc + 1) * IDLE_TIMEOUT);
+ deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
+ }
+ else
+ parkTime = deadline = 0L;
+ if (w.eventCount == ec && ctl == c) {
+ Thread wt = Thread.currentThread();
+ U.putObject(wt, PARKBLOCKER, this);
+ w.parker = wt; // emulate LockSupport.park
+ if (w.eventCount == ec && ctl == c)
+ U.park(false, parkTime); // must recheck before park
+ w.parker = null;
+ U.putObject(wt, PARKBLOCKER, null);
+ if (parkTime != 0L && ctl == c &&
+ deadline - System.nanoTime() <= 0L &&
+ U.compareAndSwapLong(this, CTL, c, pc))
+ stat = w.qlock = -1; // shrink pool
+ }
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Possibly releases (signals) a worker. Called only from scan()
+ * when a worker with apparently inactive status finds a non-empty
+ * queue. This requires revalidating all of the associated state
+ * from caller.
+ */
+ private final void helpRelease(long c, WorkQueue[] ws, WorkQueue w,
+ WorkQueue q, int b) {
+ WorkQueue v; int e, i; Thread p;
+ if (w != null && w.eventCount < 0 && (e = (int)c) > 0 &&
+ ws != null && ws.length > (i = e & SMASK) &&
+ (v = ws[i]) != null && ctl == c) {
+ long nc = (((long)(v.nextWait & E_MASK)) |
+ ((long)((int)(c >>> 32) + UAC_UNIT)) << 32);
+ int ne = (e + E_SEQ) & E_MASK;
+ if (q != null && q.base == b && w.eventCount < 0 &&
+ v.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ v.eventCount = ne;
+ if ((p = v.parker) != null)
+ U.unpark(p);
+ }
+ }
+ }
+
+ /**
+ * Tries to locate and execute tasks for a stealer of the given
+ * task, or in turn one of its stealers, Traces currentSteal ->
+ * currentJoin links looking for a thread working on a descendant
+ * of the given task and with a non-empty queue to steal back and
+ * execute tasks from. The first call to this method upon a
+ * waiting join will often entail scanning/search, (which is OK
+ * because the joiner has nothing better to do), but this method
+ * leaves hints in workers to speed up subsequent calls. The
+ * implementation is very branchy to cope with potential
+ * inconsistencies or loops encountering chains that are stale,
+ * unknown, or so long that they are likely cyclic.
+ *
+ * @param joiner the joining worker
+ * @param task the task to join
+ * @return 0 if no progress can be made, negative if task
+ * known complete, else positive
+ */
+ private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
+ int stat = 0, steps = 0; // bound to avoid cycles
+ if (task != null && joiner != null &&
+ joiner.base - joiner.top >= 0) { // hoist checks
+ restart: for (;;) {
+ ForkJoinTask<?> subtask = task; // current target
+ for (WorkQueue j = joiner, v;;) { // v is stealer of subtask
+ WorkQueue[] ws; int m, s, h;
+ if ((s = task.status) < 0) {
+ stat = s;
+ break restart;
+ }
+ if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
+ break restart; // shutting down
+ if ((v = ws[h = (j.hint | 1) & m]) == null ||
+ v.currentSteal != subtask) {
+ for (int origin = h;;) { // find stealer
+ if (((h = (h + 2) & m) & 15) == 1 &&
+ (subtask.status < 0 || j.currentJoin != subtask))
+ continue restart; // occasional staleness check
+ if ((v = ws[h]) != null &&
+ v.currentSteal == subtask) {
+ j.hint = h; // save hint
+ break;
+ }
+ if (h == origin)
+ break restart; // cannot find stealer
+ }
+ }
+ for (;;) { // help stealer or descend to its stealer
+ ForkJoinTask<?>[] a; int b;
+ if (subtask.status < 0) // surround probes with
+ continue restart; // consistency checks
+ if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
+ int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+ ForkJoinTask<?> t =
+ (ForkJoinTask<?>)U.getObjectVolatile(a, i);
+ if (subtask.status < 0 || j.currentJoin != subtask ||
+ v.currentSteal != subtask)
+ continue restart; // stale
+ stat = 1; // apparent progress
+ if (v.base == b) {
+ if (t == null)
+ break restart;
+ if (U.compareAndSwapObject(a, i, t, null)) {
+ U.putOrderedInt(v, QBASE, b + 1);
+ ForkJoinTask<?> ps = joiner.currentSteal;
+ int jt = joiner.top;
+ do {
+ joiner.currentSteal = t;
+ t.doExec(); // clear local tasks too
+ } while (task.status >= 0 &&
+ joiner.top != jt &&
+ (t = joiner.pop()) != null);
+ joiner.currentSteal = ps;
+ break restart;
+ }
+ }
+ }
+ else { // empty -- try to descend
+ ForkJoinTask<?> next = v.currentJoin;
+ if (subtask.status < 0 || j.currentJoin != subtask ||
+ v.currentSteal != subtask)
+ continue restart; // stale
+ else if (next == null || ++steps == MAX_HELP)
+ break restart; // dead-end or maybe cyclic
+ else {
+ subtask = next;
+ j = v;
+ break;
+ }
+ }
+ }
+ }
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Analog of tryHelpStealer for CountedCompleters. Tries to steal
+ * and run tasks within the target's computation.
+ *
+ * @param task the task to join
+ * @param maxTasks the maximum number of other tasks to run
+ */
+ final int helpComplete(WorkQueue joiner, CountedCompleter<?> task,
+ int maxTasks) {
+ WorkQueue[] ws; int m;
+ int s = 0;
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+ joiner != null && task != null) {
+ int j = joiner.poolIndex;
+ int scans = m + m + 1;
+ long c = 0L; // for stability check
+ for (int k = scans; ; j += 2) {
+ WorkQueue q;
+ if ((s = task.status) < 0)
+ break;
+ else if (joiner.internalPopAndExecCC(task)) {
+ if (--maxTasks <= 0) {
+ s = task.status;
+ break;
+ }
+ k = scans;
+ }
+ else if ((s = task.status) < 0)
+ break;
+ else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
+ if (--maxTasks <= 0) {
+ s = task.status;
+ break;
+ }
+ k = scans;
+ }
+ else if (--k < 0) {
+ if (c == (c = ctl))
+ break;
+ k = scans;
+ }
+ }
+ }
+ return s;
+ }
+
+ /**
+ * Tries to decrement active count (sometimes implicitly) and
+ * possibly release or create a compensating worker in preparation
+ * for blocking. Fails on contention or termination. Otherwise,
+ * adds a new thread if no idle workers are available and pool
+ * may become starved.
+ *
+ * @param c the assumed ctl value
+ */
+ final boolean tryCompensate(long c) {
+ WorkQueue[] ws = workQueues;
+ int pc = parallelism, e = (int)c, m, tc;
+ if (ws != null && (m = ws.length - 1) >= 0 && e >= 0 && ctl == c) {
+ WorkQueue w = ws[e & m];
+ if (e != 0 && w != null) {
+ Thread p;
+ long nc = ((long)(w.nextWait & E_MASK) |
+ (c & (AC_MASK|TC_MASK)));
+ int ne = (e + E_SEQ) & E_MASK;
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, c, nc)) {
+ w.eventCount = ne;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ return true; // replace with idle worker
+ }
+ }
+ else if ((tc = (short)(c >>> TC_SHIFT)) >= 0 &&
+ (int)(c >> AC_SHIFT) + pc > 1) {
+ long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ return true; // no compensation
+ }
+ else if (tc + pc < MAX_CAP) {
+ long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+ if (U.compareAndSwapLong(this, CTL, c, nc)) {
+ ForkJoinWorkerThreadFactory fac;
+ Throwable ex = null;
+ ForkJoinWorkerThread wt = null;
+ try {
+ if ((fac = factory) != null &&
+ (wt = fac.newThread(this)) != null) {
+ wt.start();
+ return true;
+ }
+ } catch (Throwable rex) {
+ ex = rex;
+ }
+ deregisterWorker(wt, ex); // clean up and return false
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Helps and/or blocks until the given task is done.
+ *
+ * @param joiner the joining worker
+ * @param task the task
+ * @return task status on exit
+ */
+ final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
+ int s = 0;
+ if (task != null && (s = task.status) >= 0 && joiner != null) {
+ ForkJoinTask<?> prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+ (s = task.status) >= 0);
+ if (s >= 0 && (task instanceof CountedCompleter))
+ s = helpComplete(joiner, (CountedCompleter<?>)task, Integer.MAX_VALUE);
+ long cc = 0; // for stability checks
+ while (s >= 0 && (s = task.status) >= 0) {
+ if ((s = tryHelpStealer(joiner, task)) == 0 &&
+ (s = task.status) >= 0) {
+ if (!tryCompensate(cc))
+ cc = ctl;
+ else {
+ if (task.trySetSignal() && (s = task.status) >= 0) {
+ synchronized (task) {
+ if (task.status >= 0) {
+ try { // see ForkJoinTask
+ task.wait(); // for explanation
+ } catch (InterruptedException ie) {
+ }
+ }
+ else
+ task.notifyAll();
+ }
+ }
+ long c; // reactivate
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl,
+ ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
+ }
+ }
+ }
+ joiner.currentJoin = prevJoin;
+ }
+ return s;
+ }
+
+ /**
+ * Stripped-down variant of awaitJoin used by timed joins. Tries
+ * to help join only while there is continuous progress. (Caller
+ * will then enter a timed wait.)
+ *
+ * @param joiner the joining worker
+ * @param task the task
+ */
+ final void helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
+ int s;
+ if (joiner != null && task != null && (s = task.status) >= 0) {
+ ForkJoinTask<?> prevJoin = joiner.currentJoin;
+ joiner.currentJoin = task;
+ do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+ (s = task.status) >= 0);
+ if (s >= 0) {
+ if (task instanceof CountedCompleter)
+ helpComplete(joiner, (CountedCompleter<?>)task, Integer.MAX_VALUE);
+ do {} while (task.status >= 0 &&
+ tryHelpStealer(joiner, task) > 0);
+ }
+ joiner.currentJoin = prevJoin;
+ }
+ }
+
+ /**
+ * Returns a (probably) non-empty steal queue, if one is found
+ * during a scan, else null. This method must be retried by
+ * caller if, by the time it tries to use the queue, it is empty.
+ */
+ private WorkQueue findNonEmptyStealQueue() {
+ int r = ThreadLocalRandom.nextSecondarySeed();
+ for (;;) {
+ int ps = plock, m; WorkQueue[] ws; WorkQueue q;
+ if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+ for (int j = (m + 1) << 2; j >= 0; --j) {
+ if ((q = ws[(((r - j) << 1) | 1) & m]) != null &&
+ q.base - q.top < 0)
+ return q;
+ }
+ }
+ if (plock == ps)
+ return null;
+ }
+ }
+
+ /**
+ * Runs tasks until {@code isQuiescent()}. We piggyback on
+ * active count ctl maintenance, but rather than blocking
+ * when tasks cannot be found, we rescan until all others cannot
+ * find tasks either.
+ */
+ final void helpQuiescePool(WorkQueue w) {
+ ForkJoinTask<?> ps = w.currentSteal;
+ for (boolean active = true;;) {
+ long c; WorkQueue q; ForkJoinTask<?> t; int b;
+ while ((t = w.nextLocalTask()) != null)
+ t.doExec();
+ if ((q = findNonEmptyStealQueue()) != null) {
+ if (!active) { // re-establish active count
+ active = true;
+ do {} while (!U.compareAndSwapLong
+ (this, CTL, c = ctl,
+ ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))));
+ }
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
+ w.runTask(t);
+ }
+ else if (active) { // decrement active count without queuing
+ long nc = ((c = ctl) & ~AC_MASK) | ((c & AC_MASK) - AC_UNIT);
+ if ((int)(nc >> AC_SHIFT) + parallelism == 0)
+ break; // bypass decrement-then-increment
+ if (U.compareAndSwapLong(this, CTL, c, nc))
+ active = false;
+ }
+ else if ((int)((c = ctl) >> AC_SHIFT) + parallelism <= 0 &&
+ U.compareAndSwapLong
+ (this, CTL, c, ((c & ~AC_MASK) |
+ ((c & AC_MASK) + AC_UNIT))))
+ break;
+ }
+ }
+
+ /**
+ * Gets and removes a local or stolen task for the given worker.
+ *
+ * @return a task, if available
+ */
+ final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
+ for (ForkJoinTask<?> t;;) {
+ WorkQueue q; int b;
+ if ((t = w.nextLocalTask()) != null)
+ return t;
+ if ((q = findNonEmptyStealQueue()) == null)
+ return null;
+ if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
+ return t;
+ }
+ }
+
+ /**
+ * Returns a cheap heuristic guide for task partitioning when
+ * programmers, frameworks, tools, or languages have little or no
+ * idea about task granularity. In essence by offering this
+ * method, we ask users only about tradeoffs in overhead vs
+ * expected throughput and its variance, rather than how finely to
+ * partition tasks.
+ *
+ * In a steady state strict (tree-structured) computation, each
+ * thread makes available for stealing enough tasks for other
+ * threads to remain active. Inductively, if all threads play by
+ * the same rules, each thread should make available only a
+ * constant number of tasks.
+ *
+ * The minimum useful constant is just 1. But using a value of 1
+ * would require immediate replenishment upon each steal to
+ * maintain enough tasks, which is infeasible. Further,
+ * partitionings/granularities of offered tasks should minimize
+ * steal rates, which in general means that threads nearer the top
+ * of computation tree should generate more than those nearer the
+ * bottom. In perfect steady state, each thread is at
+ * approximately the same level of computation tree. However,
+ * producing extra tasks amortizes the uncertainty of progress and
+ * diffusion assumptions.
+ *
+ * So, users will want to use values larger (but not much larger)
+ * than 1 to both smooth over transient shortages and hedge
+ * against uneven progress; as traded off against the cost of
+ * extra task overhead. We leave the user to pick a threshold
+ * value to compare with the results of this call to guide
+ * decisions, but recommend values such as 3.
+ *
+ * When all threads are active, it is on average OK to estimate
+ * surplus strictly locally. In steady-state, if one thread is
+ * maintaining say 2 surplus tasks, then so are others. So we can
+ * just use estimated queue length. However, this strategy alone
+ * leads to serious mis-estimates in some non-steady-state
+ * conditions (ramp-up, ramp-down, other stalls). We can detect
+ * many of these by further considering the number of "idle"
+ * threads, that are known to have zero queued tasks, so
+ * compensate by a factor of (#idle/#active) threads.
+ *
+ * Note: The approximation of #busy workers as #active workers is
+ * not very good under current signalling scheme, and should be
+ * improved.
+ */
+ static int getSurplusQueuedTaskCount() {
+ Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
+ if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
+ int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).parallelism;
+ int n = (q = wt.workQueue).top - q.base;
+ int a = (int)(pool.ctl >> AC_SHIFT) + p;
+ return n - (a > (p >>>= 1) ? 0 :
+ a > (p >>>= 1) ? 1 :
+ a > (p >>>= 1) ? 2 :
+ a > (p >>>= 1) ? 4 :
+ 8);
+ }
+ return 0;
+ }
+
+ // Termination
+
+ /**
+ * Possibly initiates and/or completes termination. The caller
+ * triggering termination runs three passes through workQueues:
+ * (0) Setting termination status, followed by wakeups of queued
+ * workers; (1) cancelling all tasks; (2) interrupting lagging
+ * threads (likely in external tasks, but possibly also blocked in
+ * joins). Each pass repeats previous steps because of potential
+ * lagging thread creation.
+ *
+ * @param now if true, unconditionally terminate, else only
+ * if no work and no active workers
+ * @param enable if true, enable shutdown when next possible
+ * @return true if now terminating or terminated
+ */
+ private boolean tryTerminate(boolean now, boolean enable) {
+ int ps;
+ if (this == common) // cannot shut down
+ return false;
+ if ((ps = plock) >= 0) { // enable by setting plock
+ if (!enable)
+ return false;
+ if ((ps & PL_LOCK) != 0 ||
+ !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+ ps = acquirePlock();
+ int nps = ((ps + PL_LOCK) & ~SHUTDOWN) | SHUTDOWN;
+ if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+ releasePlock(nps);
+ }
+ for (long c;;) {
+ if (((c = ctl) & STOP_BIT) != 0) { // already terminating
+ if ((short)(c >>> TC_SHIFT) + parallelism <= 0) {
+ synchronized (this) {
+ notifyAll(); // signal when 0 workers
+ }
+ }
+ return true;
+ }
+ if (!now) { // check if idle & no tasks
+ WorkQueue[] ws; WorkQueue w;
+ if ((int)(c >> AC_SHIFT) + parallelism > 0)
+ return false;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ if ((w = ws[i]) != null &&
+ (!w.isEmpty() ||
+ ((i & 1) != 0 && w.eventCount >= 0))) {
+ signalWork(ws, w);
+ return false;
+ }
+ }
+ }
+ }
+ if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
+ for (int pass = 0; pass < 3; ++pass) {
+ WorkQueue[] ws; WorkQueue w; Thread wt;
+ if ((ws = workQueues) != null) {
+ int n = ws.length;
+ for (int i = 0; i < n; ++i) {
+ if ((w = ws[i]) != null) {
+ w.qlock = -1;
+ if (pass > 0) {
+ w.cancelAll();
+ if (pass > 1 && (wt = w.owner) != null) {
+ if (!wt.isInterrupted()) {
+ try {
+ wt.interrupt();
+ } catch (Throwable ignore) {
+ }
+ }
+ U.unpark(wt);
+ }
+ }
+ }
+ }
+ // Wake up workers parked on event queue
+ int i, e; long cc; Thread p;
+ while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
+ (i = e & SMASK) < n && i >= 0 &&
+ (w = ws[i]) != null) {
+ long nc = ((long)(w.nextWait & E_MASK) |
+ ((cc + AC_UNIT) & AC_MASK) |
+ (cc & (TC_MASK|STOP_BIT)));
+ if (w.eventCount == (e | INT_SIGN) &&
+ U.compareAndSwapLong(this, CTL, cc, nc)) {
+ w.eventCount = (e + E_SEQ) & E_MASK;
+ w.qlock = -1;
+ if ((p = w.parker) != null)
+ U.unpark(p);
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+
+ // external operations on common pool
+
+ /**
+ * Returns common pool queue for a thread that has submitted at
+ * least one task.
+ */
+ static WorkQueue commonSubmitterQueue() {
+ ForkJoinPool p; WorkQueue[] ws; int m, z;
+ return ((z = ThreadLocalRandom.getProbe()) != 0 &&
+ (p = common) != null &&
+ (ws = p.workQueues) != null &&
+ (m = ws.length - 1) >= 0) ?
+ ws[m & z & SQMASK] : null;
+ }
+
+ /**
+ * Tries to pop the given task from submitter's queue in common pool.
+ */
+ final boolean tryExternalUnpush(ForkJoinTask<?> task) {
+ WorkQueue joiner; ForkJoinTask<?>[] a; int m, s;
+ WorkQueue[] ws = workQueues;
+ int z = ThreadLocalRandom.getProbe();
+ boolean popped = false;
+ if (ws != null && (m = ws.length - 1) >= 0 &&
+ (joiner = ws[z & m & SQMASK]) != null &&
+ joiner.base != (s = joiner.top) &&
+ (a = joiner.array) != null) {
+ long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+ if (U.getObject(a, j) == task &&
+ U.compareAndSwapInt(joiner, QLOCK, 0, 1)) {
+ if (joiner.top == s && joiner.array == a &&
+ U.compareAndSwapObject(a, j, task, null)) {
+ joiner.top = s - 1;
+ popped = true;
+ }
+ joiner.qlock = 0;
+ }
+ }
+ return popped;
+ }
+
+ final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) {
+ WorkQueue joiner; int m;
+ WorkQueue[] ws = workQueues;
+ int j = ThreadLocalRandom.getProbe();
+ int s = 0;
+ if (ws != null && (m = ws.length - 1) >= 0 &&
+ (joiner = ws[j & m & SQMASK]) != null && task != null) {
+ int scans = m + m + 1;
+ long c = 0L; // for stability check
+ j |= 1; // poll odd queues
+ for (int k = scans; ; j += 2) {
+ WorkQueue q;
+ if ((s = task.status) < 0)
+ break;
+ else if (joiner.externalPopAndExecCC(task)) {
+ if (--maxTasks <= 0) {
+ s = task.status;
+ break;
+ }
+ k = scans;
+ }
+ else if ((s = task.status) < 0)
+ break;
+ else if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
+ if (--maxTasks <= 0) {
+ s = task.status;
+ break;
+ }
+ k = scans;
+ }
+ else if (--k < 0) {
+ if (c == (c = ctl))
+ break;
+ k = scans;
+ }
+ }
+ }
+ return s;
+ }
+
+ // Exported methods
+
+ // Constructors
+
+ /**
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory},
+ * no UncaughtExceptionHandler, and non-async LIFO processing mode.
+ *
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool() {
+ this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()),
+ defaultForkJoinWorkerThreadFactory, null, false);
+ }
+
+ /**
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level, the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory},
+ * no UncaughtExceptionHandler, and non-async LIFO processing mode.
+ *
+ * @param parallelism the parallelism level
+ * @throws IllegalArgumentException if parallelism less than or
+ * equal to zero, or greater than implementation limit
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool(int parallelism) {
+ this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
+ }
+
+ /**
+ * Creates a {@code ForkJoinPool} with the given parameters.
+ *
+ * @param parallelism the parallelism level. For default value,
+ * use {@link java.lang.Runtime#availableProcessors}.
+ * @param factory the factory for creating new threads. For default value,
+ * use {@link #defaultForkJoinWorkerThreadFactory}.
+ * @param handler the handler for internal worker threads that
+ * terminate due to unrecoverable errors encountered while executing
+ * tasks. For default value, use {@code null}.
+ * @param asyncMode if true,
+ * establishes local first-in-first-out scheduling mode for forked
+ * tasks that are never joined. This mode may be more appropriate
+ * than default locally stack-based mode in applications in which
+ * worker threads only process event-style asynchronous tasks.
+ * For default value, use {@code false}.
+ * @throws IllegalArgumentException if parallelism less than or
+ * equal to zero, or greater than implementation limit
+ * @throws NullPointerException if the factory is null
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public ForkJoinPool(int parallelism,
+ ForkJoinWorkerThreadFactory factory,
+ UncaughtExceptionHandler handler,
+ boolean asyncMode) {
+ this(checkParallelism(parallelism),
+ checkFactory(factory),
+ handler,
+ (asyncMode ? FIFO_QUEUE : LIFO_QUEUE),
+ "ForkJoinPool-" + nextPoolId() + "-worker-");
+ checkPermission();
+ }
+
+ private static int checkParallelism(int parallelism) {
+ if (parallelism <= 0 || parallelism > MAX_CAP)
+ throw new IllegalArgumentException();
+ return parallelism;
+ }
+
+ private static ForkJoinWorkerThreadFactory checkFactory
+ (ForkJoinWorkerThreadFactory factory) {
+ if (factory == null)
+ throw new NullPointerException();
+ return factory;
+ }
+
+ /**
+ * Creates a {@code ForkJoinPool} with the given parameters, without
+ * any security checks or parameter validation. Invoked directly by
+ * makeCommonPool.
+ */
+ private ForkJoinPool(int parallelism,
+ ForkJoinWorkerThreadFactory factory,
+ UncaughtExceptionHandler handler,
+ int mode,
+ String workerNamePrefix) {
+ this.workerNamePrefix = workerNamePrefix;
+ this.factory = factory;
+ this.ueh = handler;
+ this.mode = (short)mode;
+ this.parallelism = (short)parallelism;
+ long np = (long)(-parallelism); // offset ctl counts
+ this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
+ }
+
+ /**
+ * Returns the common pool instance. This pool is statically
+ * constructed; its run state is unaffected by attempts to {@link
+ * #shutdown} or {@link #shutdownNow}. However this pool and any
+ * ongoing processing are automatically terminated upon program
+ * {@link System#exit}. Any program that relies on asynchronous
+ * task processing to complete before program termination should
+ * invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence},
+ * before exit.
+ *
+ * @return the common pool instance
+ * @since 1.8
+ */
+ public static ForkJoinPool commonPool() {
+ // assert common != null : "static init error";
+ return common;
+ }
+
+ // Execution methods
+
+ /**
+ * Performs the given task, returning its result upon completion.
+ * If the computation encounters an unchecked Exception or Error,
+ * it is rethrown as the outcome of this invocation. Rethrown
+ * exceptions behave in the same way as regular exceptions, but,
+ * when possible, contain stack traces (as displayed for example
+ * using {@code ex.printStackTrace()}) of both the current thread
+ * as well as the thread actually encountering the exception;
+ * minimally only the latter.
+ *
+ * @param task the task
+ * @param <T> the type of the task's result
+ * @return the task's result
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public <T> T invoke(ForkJoinTask<T> task) {
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
+ return task.join();
+ }
+
+ /**
+ * Arranges for (asynchronous) execution of the given task.
+ *
+ * @param task the task
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public void execute(ForkJoinTask<?> task) {
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
+ }
+
+ // AbstractExecutorService methods
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public void execute(Runnable task) {
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask<?> job;
+ if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+ job = (ForkJoinTask<?>) task;
+ else
+ job = new ForkJoinTask.RunnableExecuteAction(task);
+ externalPush(job);
+ }
+
+ /**
+ * Submits a ForkJoinTask for execution.
+ *
+ * @param task the task to submit
+ * @param <T> the type of the task's result
+ * @return the task
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
+ if (task == null)
+ throw new NullPointerException();
+ externalPush(task);
+ return task;
+ }
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public <T> ForkJoinTask<T> submit(Callable<T> task) {
+ ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
+ externalPush(job);
+ return job;
+ }
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public <T> ForkJoinTask<T> submit(Runnable task, T result) {
+ ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
+ externalPush(job);
+ return job;
+ }
+
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
+ public ForkJoinTask<?> submit(Runnable task) {
+ if (task == null)
+ throw new NullPointerException();
+ ForkJoinTask<?> job;
+ if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+ job = (ForkJoinTask<?>) task;
+ else
+ job = new ForkJoinTask.AdaptedRunnableAction(task);
+ externalPush(job);
+ return job;
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
+ public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
+ // In previous versions of this class, this method constructed
+ // a task to run ForkJoinTask.invokeAll, but now external
+ // invocation of multiple tasks is at least as efficient.
+ ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
+
+ boolean done = false;
+ try {
+ for (Callable<T> t : tasks) {
+ ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
+ futures.add(f);
+ externalPush(f);
+ }
+ for (int i = 0, size = futures.size(); i < size; i++)
+ ((ForkJoinTask<?>)futures.get(i)).quietlyJoin();
+ done = true;
+ return futures;
+ } finally {
+ if (!done)
+ for (int i = 0, size = futures.size(); i < size; i++)
+ futures.get(i).cancel(false);
+ }
+ }
+
+ /**
+ * Returns the factory used for constructing new workers.
+ *
+ * @return the factory used for constructing new workers
+ */
+ public ForkJoinWorkerThreadFactory getFactory() {
+ return factory;
+ }
+
+ /**
+ * Returns the handler for internal worker threads that terminate
+ * due to unrecoverable errors encountered while executing tasks.
+ *
+ * @return the handler, or {@code null} if none
+ */
+ public UncaughtExceptionHandler getUncaughtExceptionHandler() {
+ return ueh;
+ }
+
+ /**
+ * Returns the targeted parallelism level of this pool.
+ *
+ * @return the targeted parallelism level of this pool
+ */
+ public int getParallelism() {
+ int par;
+ return ((par = parallelism) > 0) ? par : 1;
+ }
+
+ /**
+ * Returns the targeted parallelism level of the common pool.
+ *
+ * @return the targeted parallelism level of the common pool
+ * @since 1.8
+ */
+ public static int getCommonPoolParallelism() {
+ return commonParallelism;
+ }
+
+ /**
+ * Returns the number of worker threads that have started but not
+ * yet terminated. The result returned by this method may differ
+ * from {@link #getParallelism} when threads are created to
+ * maintain parallelism when others are cooperatively blocked.
+ *
+ * @return the number of worker threads
+ */
+ public int getPoolSize() {
+ return parallelism + (short)(ctl >>> TC_SHIFT);
+ }
+
+ /**
+ * Returns {@code true} if this pool uses local first-in-first-out
+ * scheduling mode for forked tasks that are never joined.
+ *
+ * @return {@code true} if this pool uses async mode
+ */
+ public boolean getAsyncMode() {
+ return mode == FIFO_QUEUE;
+ }
+
+ /**
+ * Returns an estimate of the number of worker threads that are
+ * not blocked waiting to join tasks or for other managed
+ * synchronization. This method may overestimate the
+ * number of running threads.
+ *
+ * @return the number of worker threads
+ */
+ public int getRunningThreadCount() {
+ int rc = 0;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 1; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null && w.isApparentlyUnblocked())
+ ++rc;
+ }
+ }
+ return rc;
+ }
+
+ /**
+ * Returns an estimate of the number of threads that are currently
+ * stealing or executing tasks. This method may overestimate the
+ * number of active threads.
+ *
+ * @return the number of active threads
+ */
+ public int getActiveThreadCount() {
+ int r = parallelism + (int)(ctl >> AC_SHIFT);
+ return (r <= 0) ? 0 : r; // suppress momentarily negative values
+ }
+
+ /**
+ * Returns {@code true} if all worker threads are currently idle.
+ * An idle worker is one that cannot obtain a task to execute
+ * because none are available to steal from other threads, and
+ * there are no pending submissions to the pool. This method is
+ * conservative; it might not return {@code true} immediately upon
+ * idleness of all threads, but will eventually become true if
+ * threads remain inactive.
+ *
+ * @return {@code true} if all threads are currently idle
+ */
+ public boolean isQuiescent() {
+ return parallelism + (int)(ctl >> AC_SHIFT) <= 0;
+ }
+
+ /**
+ * Returns an estimate of the total number of tasks stolen from
+ * one thread's work queue by another. The reported value
+ * underestimates the actual total number of steals when the pool
+ * is not quiescent. This value may be useful for monitoring and
+ * tuning fork/join programs: in general, steal counts should be
+ * high enough to keep threads busy, but low enough to avoid
+ * overhead and contention across threads.
+ *
+ * @return the number of steals
+ */
+ public long getStealCount() {
+ long count = stealCount;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 1; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.nsteals;
+ }
+ }
+ return count;
+ }
+
+ /**
+ * Returns an estimate of the total number of tasks currently held
+ * in queues by worker threads (but not including tasks submitted
+ * to the pool that have not begun executing). This value is only
+ * an approximation, obtained by iterating across all threads in
+ * the pool. This method may be useful for tuning task
+ * granularities.
+ *
+ * @return the number of queued tasks
+ */
+ public long getQueuedTaskCount() {
+ long count = 0;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 1; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.queueSize();
+ }
+ }
+ return count;
+ }
+
+ /**
+ * Returns an estimate of the number of tasks submitted to this
+ * pool that have not yet begun executing. This method may take
+ * time proportional to the number of submissions.
+ *
+ * @return the number of queued submissions
+ */
+ public int getQueuedSubmissionCount() {
+ int count = 0;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null)
+ count += w.queueSize();
+ }
+ }
+ return count;
+ }
+
+ /**
+ * Returns {@code true} if there are any tasks submitted to this
+ * pool that have not yet begun executing.
+ *
+ * @return {@code true} if there are any queued submissions
+ */
+ public boolean hasQueuedSubmissions() {
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null && !w.isEmpty())
+ return true;
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Removes and returns the next unexecuted submission if one is
+ * available. This method may be useful in extensions to this
+ * class that re-assign work in systems with multiple pools.
+ *
+ * @return the next submission, or {@code null} if none
+ */
+ protected ForkJoinTask<?> pollSubmission() {
+ WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; i += 2) {
+ if ((w = ws[i]) != null && (t = w.poll()) != null)
+ return t;
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Removes all available unexecuted submitted and forked tasks
+ * from scheduling queues and adds them to the given collection,
+ * without altering their execution status. These may include
+ * artificially generated or wrapped tasks. This method is
+ * designed to be invoked only when the pool is known to be
+ * quiescent. Invocations at other times may not remove all
+ * tasks. A failure encountered while attempting to add elements
+ * to collection {@code c} may result in elements being in
+ * neither, either or both collections when the associated
+ * exception is thrown. The behavior of this operation is
+ * undefined if the specified collection is modified while the
+ * operation is in progress.
+ *
+ * @param c the collection to transfer elements into
+ * @return the number of elements transferred
+ */
+ protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
+ int count = 0;
+ WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ if ((w = ws[i]) != null) {
+ while ((t = w.poll()) != null) {
+ c.add(t);
+ ++count;
+ }
+ }
+ }
+ }
+ return count;
+ }
+
+ /**
+ * Returns a string identifying this pool, as well as its state,
+ * including indications of run state, parallelism level, and
+ * worker and task counts.
+ *
+ * @return a string identifying this pool, as well as its state
+ */
+ public String toString() {
+ // Use a single pass through workQueues to collect counts
+ long qt = 0L, qs = 0L; int rc = 0;
+ long st = stealCount;
+ long c = ctl;
+ WorkQueue[] ws; WorkQueue w;
+ if ((ws = workQueues) != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ if ((w = ws[i]) != null) {
+ int size = w.queueSize();
+ if ((i & 1) == 0)
+ qs += size;
+ else {
+ qt += size;
+ st += w.nsteals;
+ if (w.isApparentlyUnblocked())
+ ++rc;
+ }
+ }
+ }
+ }
+ int pc = parallelism;
+ int tc = pc + (short)(c >>> TC_SHIFT);
+ int ac = pc + (int)(c >> AC_SHIFT);
+ if (ac < 0) // ignore transient negative
+ ac = 0;
+ String level;
+ if ((c & STOP_BIT) != 0)
+ level = (tc == 0) ? "Terminated" : "Terminating";
+ else
+ level = plock < 0 ? "Shutting down" : "Running";
+ return super.toString() +
+ "[" + level +
+ ", parallelism = " + pc +
+ ", size = " + tc +
+ ", active = " + ac +
+ ", running = " + rc +
+ ", steals = " + st +
+ ", tasks = " + qt +
+ ", submissions = " + qs +
+ "]";
+ }
+
+ /**
+ * Possibly initiates an orderly shutdown in which previously
+ * submitted tasks are executed, but no new tasks will be
+ * accepted. Invocation has no effect on execution state if this
+ * is the {@link #commonPool()}, and no additional effect if
+ * already shut down. Tasks that are in the process of being
+ * submitted concurrently during the course of this method may or
+ * may not be rejected.
+ *
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public void shutdown() {
+ checkPermission();
+ tryTerminate(false, true);
+ }
+
+ /**
+ * Possibly attempts to cancel and/or stop all tasks, and reject
+ * all subsequently submitted tasks. Invocation has no effect on
+ * execution state if this is the {@link #commonPool()}, and no
+ * additional effect if already shut down. Otherwise, tasks that
+ * are in the process of being submitted or executed concurrently
+ * during the course of this method may or may not be
+ * rejected. This method cancels both existing and unexecuted
+ * tasks, in order to permit termination in the presence of task
+ * dependencies. So the method always returns an empty list
+ * (unlike the case for some other Executors).
+ *
+ * @return an empty list
+ * @throws SecurityException if a security manager exists and
+ * the caller is not permitted to modify threads
+ * because it does not hold {@link
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
+ */
+ public List<Runnable> shutdownNow() {
+ checkPermission();
+ tryTerminate(true, true);
+ return Collections.emptyList();
+ }
+
+ /**
+ * Returns {@code true} if all tasks have completed following shut down.
+ *
+ * @return {@code true} if all tasks have completed following shut down
+ */
+ public boolean isTerminated() {
+ long c = ctl;
+ return ((c & STOP_BIT) != 0L &&
+ (short)(c >>> TC_SHIFT) + parallelism <= 0);
+ }
+
+ /**
+ * Returns {@code true} if the process of termination has
+ * commenced but not yet completed. This method may be useful for
+ * debugging. A return of {@code true} reported a sufficient
+ * period after shutdown may indicate that submitted tasks have
+ * ignored or suppressed interruption, or are waiting for I/O,
+ * causing this executor not to properly terminate. (See the
+ * advisory notes for class {@link ForkJoinTask} stating that
+ * tasks should not normally entail blocking operations. But if
+ * they do, they must abort them on interrupt.)
+ *
+ * @return {@code true} if terminating but not yet terminated
+ */
+ public boolean isTerminating() {
+ long c = ctl;
+ return ((c & STOP_BIT) != 0L &&
+ (short)(c >>> TC_SHIFT) + parallelism > 0);
+ }
+
+ /**
+ * Returns {@code true} if this pool has been shut down.
+ *
+ * @return {@code true} if this pool has been shut down
+ */
+ public boolean isShutdown() {
+ return plock < 0;
+ }
+
+ /**
+ * Blocks until all tasks have completed execution after a
+ * shutdown request, or the timeout occurs, or the current thread
+ * is interrupted, whichever happens first. Because the {@link
+ * #commonPool()} never terminates until program shutdown, when
+ * applied to the common pool, this method is equivalent to {@link
+ * #awaitQuiescence(long, TimeUnit)} but always returns {@code false}.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return {@code true} if this executor terminated and
+ * {@code false} if the timeout elapsed before termination
+ * @throws InterruptedException if interrupted while waiting
+ */
+ public boolean awaitTermination(long timeout, TimeUnit unit)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (this == common) {
+ awaitQuiescence(timeout, unit);
+ return false;
+ }
+ long nanos = unit.toNanos(timeout);
+ if (isTerminated())
+ return true;
+ if (nanos <= 0L)
+ return false;
+ long deadline = System.nanoTime() + nanos;
+ synchronized (this) {
+ for (;;) {
+ if (isTerminated())
+ return true;
+ if (nanos <= 0L)
+ return false;
+ long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
+ wait(millis > 0L ? millis : 1L);
+ nanos = deadline - System.nanoTime();
+ }
+ }
+ }
+
+ /**
+ * If called by a ForkJoinTask operating in this pool, equivalent
+ * in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise,
+ * waits and/or attempts to assist performing tasks until this
+ * pool {@link #isQuiescent} or the indicated timeout elapses.
+ *
+ * @param timeout the maximum time to wait
+ * @param unit the time unit of the timeout argument
+ * @return {@code true} if quiescent; {@code false} if the
+ * timeout elapsed.
+ */
+ public boolean awaitQuiescence(long timeout, TimeUnit unit) {
+ long nanos = unit.toNanos(timeout);
+ ForkJoinWorkerThread wt;
+ Thread thread = Thread.currentThread();
+ if ((thread instanceof ForkJoinWorkerThread) &&
+ (wt = (ForkJoinWorkerThread)thread).pool == this) {
+ helpQuiescePool(wt.workQueue);
+ return true;
+ }
+ long startTime = System.nanoTime();
+ WorkQueue[] ws;
+ int r = 0, m;
+ boolean found = true;
+ while (!isQuiescent() && (ws = workQueues) != null &&
+ (m = ws.length - 1) >= 0) {
+ if (!found) {
+ if ((System.nanoTime() - startTime) > nanos)
+ return false;
+ Thread.yield(); // cannot block
+ }
+ found = false;
+ for (int j = (m + 1) << 2; j >= 0; --j) {
+ ForkJoinTask<?> t; WorkQueue q; int b;
+ if ((q = ws[r++ & m]) != null && (b = q.base) - q.top < 0) {
+ found = true;
+ if ((t = q.pollAt(b)) != null)
+ t.doExec();
+ break;
+ }
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Waits and/or attempts to assist performing tasks indefinitely
+ * until the {@link #commonPool()} {@link #isQuiescent}.
+ */
+ static void quiesceCommonPool() {
+ common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
+ }
+
+ /**
+ * Interface for extending managed parallelism for tasks running
+ * in {@link ForkJoinPool}s.
+ *
+ * <p>A {@code ManagedBlocker} provides two methods. Method
+ * {@code isReleasable} must return {@code true} if blocking is
+ * not necessary. Method {@code block} blocks the current thread
+ * if necessary (perhaps internally invoking {@code isReleasable}
+ * before actually blocking). These actions are performed by any
+ * thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}.
+ * The unusual methods in this API accommodate synchronizers that
+ * may, but don't usually, block for long periods. Similarly, they
+ * allow more efficient internal handling of cases in which
+ * additional workers may be, but usually are not, needed to
+ * ensure sufficient parallelism. Toward this end,
+ * implementations of method {@code isReleasable} must be amenable
+ * to repeated invocation.
+ *
+ * <p>For example, here is a ManagedBlocker based on a
+ * ReentrantLock:
+ * <pre> {@code
+ * class ManagedLocker implements ManagedBlocker {
+ * final ReentrantLock lock;
+ * boolean hasLock = false;
+ * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
+ * public boolean block() {
+ * if (!hasLock)
+ * lock.lock();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return hasLock || (hasLock = lock.tryLock());
+ * }
+ * }}</pre>
+ *
+ * <p>Here is a class that possibly blocks waiting for an
+ * item on a given queue:
+ * <pre> {@code
+ * class QueueTaker<E> implements ManagedBlocker {
+ * final BlockingQueue<E> queue;
+ * volatile E item = null;
+ * QueueTaker(BlockingQueue<E> q) { this.queue = q; }
+ * public boolean block() throws InterruptedException {
+ * if (item == null)
+ * item = queue.take();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return item != null || (item = queue.poll()) != null;
+ * }
+ * public E getItem() { // call after pool.managedBlock completes
+ * return item;
+ * }
+ * }}</pre>
+ */
+ public static interface ManagedBlocker {
+ /**
+ * Possibly blocks the current thread, for example waiting for
+ * a lock or condition.
+ *
+ * @return {@code true} if no additional blocking is necessary
+ * (i.e., if isReleasable would return true)
+ * @throws InterruptedException if interrupted while waiting
+ * (the method is not required to do so, but is allowed to)
+ */
+ boolean block() throws InterruptedException;
+
+ /**
+ * Returns {@code true} if blocking is unnecessary.
+ * @return {@code true} if blocking is unnecessary
+ */
+ boolean isReleasable();
+ }
+
+ /**
+ * Blocks in accord with the given blocker. If the current thread
+ * is a {@link ForkJoinWorkerThread}, this method possibly
+ * arranges for a spare thread to be activated if necessary to
+ * ensure sufficient parallelism while the current thread is blocked.
+ *
+ * <p>If the caller is not a {@link ForkJoinTask}, this method is
+ * behaviorally equivalent to
+ * <pre> {@code
+ * while (!blocker.isReleasable())
+ * if (blocker.block())
+ * return;
+ * }</pre>
+ *
+ * If the caller is a {@code ForkJoinTask}, then the pool may
+ * first be expanded to ensure parallelism, and later adjusted.
+ *
+ * @param blocker the blocker
+ * @throws InterruptedException if blocker.block did so
+ */
+ public static void managedBlock(ManagedBlocker blocker)
+ throws InterruptedException {
+ Thread t = Thread.currentThread();
+ if (t instanceof ForkJoinWorkerThread) {
+ ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
+ while (!blocker.isReleasable()) {
+ if (p.tryCompensate(p.ctl)) {
+ try {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ } finally {
+ p.incrementActiveCount();
+ }
+ break;
+ }
+ }
+ }
+ else {
+ do {} while (!blocker.isReleasable() &&
+ !blocker.block());
+ }
+ }
+
+ // AbstractExecutorService overrides. These rely on undocumented
+ // fact that ForkJoinTask.adapt returns ForkJoinTasks that also
+ // implement RunnableFuture.
+
+ protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
+ return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
+ }
+
+ protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
+ return new ForkJoinTask.AdaptedCallable<T>(callable);
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe U;
+ private static final long CTL;
+ private static final long PARKBLOCKER;
+ private static final int ABASE;
+ private static final int ASHIFT;
+ private static final long STEALCOUNT;
+ private static final long PLOCK;
+ private static final long INDEXSEED;
+ private static final long QBASE;
+ private static final long QLOCK;
+
+ static {
+ // initialize field offsets for CAS etc
+ try {
+ U = sun.misc.Unsafe.getUnsafe();
+ Class<?> k = ForkJoinPool.class;
+ CTL = U.objectFieldOffset
+ (k.getDeclaredField("ctl"));
+ STEALCOUNT = U.objectFieldOffset
+ (k.getDeclaredField("stealCount"));
+ PLOCK = U.objectFieldOffset
+ (k.getDeclaredField("plock"));
+ INDEXSEED = U.objectFieldOffset
+ (k.getDeclaredField("indexSeed"));
+ Class<?> tk = Thread.class;
+ PARKBLOCKER = U.objectFieldOffset
+ (tk.getDeclaredField("parkBlocker"));
+ Class<?> wk = WorkQueue.class;
+ QBASE = U.objectFieldOffset
+ (wk.getDeclaredField("base"));
+ QLOCK = U.objectFieldOffset
+ (wk.getDeclaredField("qlock"));
+ Class<?> ak = ForkJoinTask[].class;
+ ABASE = U.arrayBaseOffset(ak);
+ int scale = U.arrayIndexScale(ak);
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+
+ defaultForkJoinWorkerThreadFactory =
+ new DefaultForkJoinWorkerThreadFactory();
+ modifyThreadPermission = new RuntimePermission("modifyThread");
+
+ common = java.security.AccessController.doPrivileged
+ (new java.security.PrivilegedAction<ForkJoinPool>() {
+ public ForkJoinPool run() { return makeCommonPool(); }});
+ int par = common.parallelism; // report 1 even if threads disabled
+ commonParallelism = par > 0 ? par : 1;
+ }
+
+ /**
+ * Creates and returns the common pool, respecting user settings
+ * specified via system properties.
+ */
+ private static ForkJoinPool makeCommonPool() {
+ int parallelism = -1;
+ ForkJoinWorkerThreadFactory factory = null;
+ UncaughtExceptionHandler handler = null;
+ try { // ignore exceptions in accessing/parsing properties
+ String pp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.parallelism");
+ String fp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.threadFactory");
+ String hp = System.getProperty
+ ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
+ if (pp != null)
+ parallelism = Integer.parseInt(pp);
+ if (fp != null)
+ factory = ((ForkJoinWorkerThreadFactory)ClassLoader.
+ getSystemClassLoader().loadClass(fp).newInstance());
+ if (hp != null)
+ handler = ((UncaughtExceptionHandler)ClassLoader.
+ getSystemClassLoader().loadClass(hp).newInstance());
+ } catch (Exception ignore) {
+ }
+ if (factory == null) {
+ if (System.getSecurityManager() == null)
+ factory = defaultForkJoinWorkerThreadFactory;
+ else // use security-managed default
+ factory = new InnocuousForkJoinWorkerThreadFactory();
+ }
+ if (parallelism < 0 && // default 1 less than #cores
+ (parallelism = Runtime.getRuntime().availableProcessors() - 1) <= 0)
+ parallelism = 1;
+ if (parallelism > MAX_CAP)
+ parallelism = MAX_CAP;
+ return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE,
+ "ForkJoinPool.commonPool-worker-");
+ }
+
+ /**
+ * Factory for innocuous worker threads
+ */
+ static final class InnocuousForkJoinWorkerThreadFactory
+ implements ForkJoinWorkerThreadFactory {
+
+ /**
+ * An ACC to restrict permissions for the factory itself.
+ * The constructed workers have no permissions set.
+ */
+ private static final AccessControlContext innocuousAcc;
+ static {
+ Permissions innocuousPerms = new Permissions();
+ innocuousPerms.add(modifyThreadPermission);
+ innocuousPerms.add(new RuntimePermission(
+ "enableContextClassLoaderOverride"));
+ innocuousPerms.add(new RuntimePermission(
+ "modifyThreadGroup"));
+ innocuousAcc = new AccessControlContext(new ProtectionDomain[] {
+ new ProtectionDomain(null, innocuousPerms)
+ });
+ }
+
+ public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+ return (ForkJoinWorkerThread.InnocuousForkJoinWorkerThread)
+ java.security.AccessController.doPrivileged(
+ new java.security.PrivilegedAction<ForkJoinWorkerThread>() {
+ public ForkJoinWorkerThread run() {
+ return new ForkJoinWorkerThread.
+ InnocuousForkJoinWorkerThread(pool);
+ }}, innocuousAcc);
+ }
+ }
+
+}
diff --git a/openjdk/response.txt b/openjdk/response.txt
index 86e08a3f..409d55c9 100644
--- a/openjdk/response.txt
+++ b/openjdk/response.txt
@@ -42,6 +42,7 @@
java/net/*.class
java/nio/*.class
java/security/*.class
+ java/util/concurrent/*.class
java/util/concurrent/locks/*.class
gnu/java/util/*.class
sun/misc/*.class
generated by cgit v1.2.3 (git 2.25.1) at 2024-09-05 07:46:59 +0300