1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
|
'use strict';
// HOW and WHY the timers implementation works the way it does.
//
// Timers are crucial to Node.js. Internally, any TCP I/O connection creates a
// timer so that we can time out of connections. Additionally, many user
// libraries and applications also use timers. As such there may be a
// significantly large amount of timeouts scheduled at any given time.
// Therefore, it is very important that the timers implementation is performant
// and efficient.
//
// Note: It is suggested you first read through the lib/internal/linkedlist.js
// linked list implementation, since timers depend on it extensively. It can be
// somewhat counter-intuitive at first, as it is not actually a class. Instead,
// it is a set of helpers that operate on an existing object.
//
// In order to be as performant as possible, the architecture and data
// structures are designed so that they are optimized to handle the following
// use cases as efficiently as possible:
// - Adding a new timer. (insert)
// - Removing an existing timer. (remove)
// - Handling a timer timing out. (timeout)
//
// Whenever possible, the implementation tries to make the complexity of these
// operations as close to constant-time as possible.
// (So that performance is not impacted by the number of scheduled timers.)
//
// Object maps are kept which contain linked lists keyed by their duration in
// milliseconds.
//
/* eslint-disable node-core/non-ascii-character */
//
// ╔════ > Object Map
// ║
// ╠══
// ║ lists: { '40': { }, '320': { etc } } (keys of millisecond duration)
// ╚══ ┌────┘
// │
// ╔══ │
// ║ TimersList { _idleNext: { }, _idlePrev: (self) }
// ║ ┌────────────────┘
// ║ ╔══ │ ^
// ║ ║ { _idleNext: { }, _idlePrev: { }, _onTimeout: (callback) }
// ║ ║ ┌───────────┘
// ║ ║ │ ^
// ║ ║ { _idleNext: { etc }, _idlePrev: { }, _onTimeout: (callback) }
// ╠══ ╠══
// ║ ║
// ║ ╚════ > Actual JavaScript timeouts
// ║
// ╚════ > Linked List
//
/* eslint-enable node-core/non-ascii-character */
//
// With this, virtually constant-time insertion (append), removal, and timeout
// is possible in the JavaScript layer. Any one list of timers is able to be
// sorted by just appending to it because all timers within share the same
// duration. Therefore, any timer added later will always have been scheduled to
// timeout later, thus only needing to be appended.
// Removal from an object-property linked list is also virtually constant-time
// as can be seen in the lib/internal/linkedlist.js implementation.
// Timeouts only need to process any timers currently due to expire, which will
// always be at the beginning of the list for reasons stated above. Any timers
// after the first one encountered that does not yet need to timeout will also
// always be due to timeout at a later time.
//
// Less-than constant time operations are thus contained in two places:
// The PriorityQueue — an efficient binary heap implementation that does all
// operations in worst-case O(log n) time — which manages the order of expiring
// Timeout lists and the object map lookup of a specific list by the duration of
// timers within (or creation of a new list). However, these operations combined
// have shown to be trivial in comparison to other timers architectures.
const {
MathMax,
MathTrunc,
NumberMIN_SAFE_INTEGER,
ObjectCreate,
Symbol,
} = primordials;
const {
scheduleTimer,
toggleTimerRef,
getLibuvNow,
immediateInfo,
toggleImmediateRef
} = internalBinding('timers');
const {
getDefaultTriggerAsyncId,
newAsyncId,
initHooksExist,
destroyHooksExist,
// The needed emit*() functions.
emitInit,
emitBefore,
emitAfter,
emitDestroy,
} = require('internal/async_hooks');
// Symbols for storing async id state.
const async_id_symbol = Symbol('asyncId');
const trigger_async_id_symbol = Symbol('triggerId');
const kHasPrimitive = Symbol('kHasPrimitive');
const {
ERR_INVALID_CALLBACK,
ERR_OUT_OF_RANGE
} = require('internal/errors').codes;
const { validateNumber } = require('internal/validators');
const L = require('internal/linkedlist');
const PriorityQueue = require('internal/priority_queue');
const { inspect } = require('internal/util/inspect');
let debug = require('internal/util/debuglog').debuglog('timer', (fn) => {
debug = fn;
});
// *Must* match Environment::ImmediateInfo::Fields in src/env.h.
const kCount = 0;
const kRefCount = 1;
const kHasOutstanding = 2;
// Timeout values > TIMEOUT_MAX are set to 1.
const TIMEOUT_MAX = 2 ** 31 - 1;
let timerListId = NumberMIN_SAFE_INTEGER;
const kRefed = Symbol('refed');
// Create a single linked list instance only once at startup
const immediateQueue = new ImmediateList();
let nextExpiry = Infinity;
let refCount = 0;
// This is a priority queue with a custom sorting function that first compares
// the expiry times of two lists and if they're the same then compares their
// individual IDs to determine which list was created first.
const timerListQueue = new PriorityQueue(compareTimersLists, setPosition);
// Object map containing linked lists of timers, keyed and sorted by their
// duration in milliseconds.
//
// - key = time in milliseconds
// - value = linked list
const timerListMap = ObjectCreate(null);
function initAsyncResource(resource, type) {
const asyncId = resource[async_id_symbol] = newAsyncId();
const triggerAsyncId =
resource[trigger_async_id_symbol] = getDefaultTriggerAsyncId();
if (initHooksExist())
emitInit(asyncId, type, triggerAsyncId, resource);
}
// Timer constructor function.
// The entire prototype is defined in lib/timers.js
function Timeout(callback, after, args, isRepeat, isRefed) {
after *= 1; // Coalesce to number or NaN
if (!(after >= 1 && after <= TIMEOUT_MAX)) {
if (after > TIMEOUT_MAX) {
process.emitWarning(`${after} does not fit into` +
' a 32-bit signed integer.' +
'\nTimeout duration was set to 1.',
'TimeoutOverflowWarning');
}
after = 1; // Schedule on next tick, follows browser behavior
}
this._idleTimeout = after;
this._idlePrev = this;
this._idleNext = this;
this._idleStart = null;
// This must be set to null first to avoid function tracking
// on the hidden class, revisit in V8 versions after 6.2
this._onTimeout = null;
this._onTimeout = callback;
this._timerArgs = args;
this._repeat = isRepeat ? after : null;
this._destroyed = false;
if (isRefed)
incRefCount();
this[kRefed] = isRefed;
this[kHasPrimitive] = false;
initAsyncResource(this, 'Timeout');
}
// Make sure the linked list only shows the minimal necessary information.
Timeout.prototype[inspect.custom] = function(_, options) {
return inspect(this, {
...options,
// Only inspect one level.
depth: 0,
// It should not recurse.
customInspect: false
});
};
Timeout.prototype.refresh = function() {
if (this[kRefed])
active(this);
else
unrefActive(this);
return this;
};
Timeout.prototype.unref = function() {
if (this[kRefed]) {
this[kRefed] = false;
if (!this._destroyed)
decRefCount();
}
return this;
};
Timeout.prototype.ref = function() {
if (!this[kRefed]) {
this[kRefed] = true;
if (!this._destroyed)
incRefCount();
}
return this;
};
Timeout.prototype.hasRef = function() {
return this[kRefed];
};
function TimersList(expiry, msecs) {
this._idleNext = this; // Create the list with the linkedlist properties to
this._idlePrev = this; // Prevent any unnecessary hidden class changes.
this.expiry = expiry;
this.id = timerListId++;
this.msecs = msecs;
this.priorityQueuePosition = null;
}
// Make sure the linked list only shows the minimal necessary information.
TimersList.prototype[inspect.custom] = function(_, options) {
return inspect(this, {
...options,
// Only inspect one level.
depth: 0,
// It should not recurse.
customInspect: false
});
};
// A linked list for storing `setImmediate()` requests
function ImmediateList() {
this.head = null;
this.tail = null;
}
// Appends an item to the end of the linked list, adjusting the current tail's
// next pointer and the item's previous pointer where applicable
ImmediateList.prototype.append = function(item) {
if (this.tail !== null) {
this.tail._idleNext = item;
item._idlePrev = this.tail;
} else {
this.head = item;
}
this.tail = item;
};
// Removes an item from the linked list, adjusting the pointers of adjacent
// items and the linked list's head or tail pointers as necessary
ImmediateList.prototype.remove = function(item) {
if (item._idleNext !== null) {
item._idleNext._idlePrev = item._idlePrev;
}
if (item._idlePrev !== null) {
item._idlePrev._idleNext = item._idleNext;
}
if (item === this.head)
this.head = item._idleNext;
if (item === this.tail)
this.tail = item._idlePrev;
item._idleNext = null;
item._idlePrev = null;
};
function incRefCount() {
if (refCount++ === 0)
toggleTimerRef(true);
}
function decRefCount() {
if (--refCount === 0)
toggleTimerRef(false);
}
// Schedule or re-schedule a timer.
// The item must have been enroll()'d first.
function active(item) {
insertGuarded(item, true);
}
// Internal APIs that need timeouts should use `unrefActive()` instead of
// `active()` so that they do not unnecessarily keep the process open.
function unrefActive(item) {
insertGuarded(item, false);
}
// The underlying logic for scheduling or re-scheduling a timer.
//
// Appends a timer onto the end of an existing timers list, or creates a new
// list if one does not already exist for the specified timeout duration.
function insertGuarded(item, refed, start) {
const msecs = item._idleTimeout;
if (msecs < 0 || msecs === undefined)
return;
insert(item, msecs, start);
const isDestroyed = item._destroyed;
if (isDestroyed || !item[async_id_symbol]) {
item._destroyed = false;
initAsyncResource(item, 'Timeout');
}
if (isDestroyed) {
if (refed)
incRefCount();
} else if (refed === !item[kRefed]) {
if (refed)
incRefCount();
else
decRefCount();
}
item[kRefed] = refed;
}
function insert(item, msecs, start = getLibuvNow()) {
// Truncate so that accuracy of sub-millisecond timers is not assumed.
msecs = MathTrunc(msecs);
item._idleStart = start;
// Use an existing list if there is one, otherwise we need to make a new one.
let list = timerListMap[msecs];
if (list === undefined) {
debug('no %d list was found in insert, creating a new one', msecs);
const expiry = start + msecs;
timerListMap[msecs] = list = new TimersList(expiry, msecs);
timerListQueue.insert(list);
if (nextExpiry > expiry) {
scheduleTimer(msecs);
nextExpiry = expiry;
}
}
L.append(list, item);
}
function setUnrefTimeout(callback, after) {
// Type checking identical to setTimeout()
if (typeof callback !== 'function') {
throw new ERR_INVALID_CALLBACK(callback);
}
const timer = new Timeout(callback, after, undefined, false, false);
insert(timer, timer._idleTimeout);
return timer;
}
// Type checking used by timers.enroll() and Socket#setTimeout()
function getTimerDuration(msecs, name) {
validateNumber(msecs, name);
if (msecs < 0 || !isFinite(msecs)) {
throw new ERR_OUT_OF_RANGE(name, 'a non-negative finite number', msecs);
}
// Ensure that msecs fits into signed int32
if (msecs > TIMEOUT_MAX) {
process.emitWarning(`${msecs} does not fit into a 32-bit signed integer.` +
`\nTimer duration was truncated to ${TIMEOUT_MAX}.`,
'TimeoutOverflowWarning');
return TIMEOUT_MAX;
}
return msecs;
}
function compareTimersLists(a, b) {
const expiryDiff = a.expiry - b.expiry;
if (expiryDiff === 0) {
if (a.id < b.id)
return -1;
if (a.id > b.id)
return 1;
}
return expiryDiff;
}
function setPosition(node, pos) {
node.priorityQueuePosition = pos;
}
function getTimerCallbacks(runNextTicks) {
// If an uncaught exception was thrown during execution of immediateQueue,
// this queue will store all remaining Immediates that need to run upon
// resolution of all error handling (if process is still alive).
const outstandingQueue = new ImmediateList();
function processImmediate() {
const queue = outstandingQueue.head !== null ?
outstandingQueue : immediateQueue;
let immediate = queue.head;
// Clear the linked list early in case new `setImmediate()`
// calls occur while immediate callbacks are executed
if (queue !== outstandingQueue) {
queue.head = queue.tail = null;
immediateInfo[kHasOutstanding] = 1;
}
let prevImmediate;
let ranAtLeastOneImmediate = false;
while (immediate !== null) {
if (ranAtLeastOneImmediate)
runNextTicks();
else
ranAtLeastOneImmediate = true;
// It's possible for this current Immediate to be cleared while executing
// the next tick queue above, which means we need to use the previous
// Immediate's _idleNext which is guaranteed to not have been cleared.
if (immediate._destroyed) {
outstandingQueue.head = immediate = prevImmediate._idleNext;
continue;
}
immediate._destroyed = true;
immediateInfo[kCount]--;
if (immediate[kRefed])
immediateInfo[kRefCount]--;
immediate[kRefed] = null;
prevImmediate = immediate;
const asyncId = immediate[async_id_symbol];
emitBefore(asyncId, immediate[trigger_async_id_symbol], immediate);
try {
const argv = immediate._argv;
if (!argv)
immediate._onImmediate();
else
immediate._onImmediate(...argv);
} finally {
immediate._onImmediate = null;
if (destroyHooksExist())
emitDestroy(asyncId);
outstandingQueue.head = immediate = immediate._idleNext;
}
emitAfter(asyncId);
}
if (queue === outstandingQueue)
outstandingQueue.head = null;
immediateInfo[kHasOutstanding] = 0;
}
function processTimers(now) {
debug('process timer lists %d', now);
nextExpiry = Infinity;
let list;
let ranAtLeastOneList = false;
while (list = timerListQueue.peek()) {
if (list.expiry > now) {
nextExpiry = list.expiry;
return refCount > 0 ? nextExpiry : -nextExpiry;
}
if (ranAtLeastOneList)
runNextTicks();
else
ranAtLeastOneList = true;
listOnTimeout(list, now);
}
return 0;
}
function listOnTimeout(list, now) {
const msecs = list.msecs;
debug('timeout callback %d', msecs);
let ranAtLeastOneTimer = false;
let timer;
while (timer = L.peek(list)) {
const diff = now - timer._idleStart;
// Check if this loop iteration is too early for the next timer.
// This happens if there are more timers scheduled for later in the list.
if (diff < msecs) {
list.expiry = MathMax(timer._idleStart + msecs, now + 1);
list.id = timerListId++;
timerListQueue.percolateDown(1);
debug('%d list wait because diff is %d', msecs, diff);
return;
}
if (ranAtLeastOneTimer)
runNextTicks();
else
ranAtLeastOneTimer = true;
// The actual logic for when a timeout happens.
L.remove(timer);
const asyncId = timer[async_id_symbol];
if (!timer._onTimeout) {
if (!timer._destroyed) {
timer._destroyed = true;
if (timer[kRefed])
refCount--;
if (destroyHooksExist())
emitDestroy(asyncId);
}
continue;
}
emitBefore(asyncId, timer[trigger_async_id_symbol], timer);
let start;
if (timer._repeat)
start = getLibuvNow();
try {
const args = timer._timerArgs;
if (args === undefined)
timer._onTimeout();
else
timer._onTimeout(...args);
} finally {
if (timer._repeat && timer._idleTimeout !== -1) {
timer._idleTimeout = timer._repeat;
insert(timer, timer._idleTimeout, start);
} else if (!timer._idleNext && !timer._idlePrev && !timer._destroyed) {
timer._destroyed = true;
if (timer[kRefed])
refCount--;
if (destroyHooksExist())
emitDestroy(asyncId);
}
}
emitAfter(asyncId);
}
// If `L.peek(list)` returned nothing, the list was either empty or we have
// called all of the timer timeouts.
// As such, we can remove the list from the object map and
// the PriorityQueue.
debug('%d list empty', msecs);
// The current list may have been removed and recreated since the reference
// to `list` was created. Make sure they're the same instance of the list
// before destroying.
if (list === timerListMap[msecs]) {
delete timerListMap[msecs];
timerListQueue.shift();
}
}
return {
processImmediate,
processTimers
};
}
class Immediate {
constructor(callback, args) {
this._idleNext = null;
this._idlePrev = null;
this._onImmediate = callback;
this._argv = args;
this._destroyed = false;
this[kRefed] = false;
initAsyncResource(this, 'Immediate');
this.ref();
immediateInfo[kCount]++;
immediateQueue.append(this);
}
ref() {
if (this[kRefed] === false) {
this[kRefed] = true;
if (immediateInfo[kRefCount]++ === 0)
toggleImmediateRef(true);
}
return this;
}
unref() {
if (this[kRefed] === true) {
this[kRefed] = false;
if (--immediateInfo[kRefCount] === 0)
toggleImmediateRef(false);
}
return this;
}
hasRef() {
return !!this[kRefed];
}
}
module.exports = {
TIMEOUT_MAX,
kTimeout: Symbol('timeout'), // For hiding Timeouts on other internals.
async_id_symbol,
trigger_async_id_symbol,
Timeout,
Immediate,
kRefed,
kHasPrimitive,
initAsyncResource,
setUnrefTimeout,
getTimerDuration,
immediateQueue,
getTimerCallbacks,
immediateInfoFields: {
kCount,
kRefCount,
kHasOutstanding
},
active,
unrefActive,
insert,
timerListMap,
timerListQueue,
decRefCount,
incRefCount
};
|