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Diffstat (limited to 'extern/ceres/internal/ceres/thread_pool.h')
-rw-r--r-- | extern/ceres/internal/ceres/thread_pool.h | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/extern/ceres/internal/ceres/thread_pool.h b/extern/ceres/internal/ceres/thread_pool.h new file mode 100644 index 00000000000..1ebb52eb6b4 --- /dev/null +++ b/extern/ceres/internal/ceres/thread_pool.h @@ -0,0 +1,120 @@ +// Ceres Solver - A fast non-linear least squares minimizer +// Copyright 2018 Google Inc. All rights reserved. +// http://ceres-solver.org/ +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are met: +// +// * Redistributions of source code must retain the above copyright notice, +// this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above copyright notice, +// this list of conditions and the following disclaimer in the documentation +// and/or other materials provided with the distribution. +// * Neither the name of Google Inc. nor the names of its contributors may be +// used to endorse or promote products derived from this software without +// specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" +// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE +// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR +// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF +// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS +// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN +// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) +// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +// POSSIBILITY OF SUCH DAMAGE. +// +// Author: vitus@google.com (Michael Vitus) + +#ifndef CERES_INTERNAL_THREAD_POOL_H_ +#define CERES_INTERNAL_THREAD_POOL_H_ + +#include <functional> +#include <mutex> +#include <thread> +#include <vector> + +#include "ceres/concurrent_queue.h" + +namespace ceres { +namespace internal { + +// A thread-safe thread pool with an unbounded task queue and a resizable number +// of workers. The size of the thread pool can be increased but never decreased +// in order to support the largest number of threads requested. The ThreadPool +// has three states: +// +// (1) The thread pool size is zero. Tasks may be added to the thread pool via +// AddTask but they will not be executed until the thread pool is resized. +// +// (2) The thread pool size is greater than zero. Tasks may be added to the +// thread pool and will be executed as soon as a worker is available. The +// thread pool may be resized while the thread pool is running. +// +// (3) The thread pool is destructing. The thread pool will signal all the +// workers to stop. The workers will finish all of the tasks that have already +// been added to the thread pool. +// +class ThreadPool { + public: + // Returns the maximum number of hardware threads. + static int MaxNumThreadsAvailable(); + + // Default constructor with no active threads. We allow instantiating a + // thread pool with no threads to support the use case of single threaded + // Ceres where everything will be executed on the main thread. For single + // threaded execution this has two benefits: avoid any overhead as threads + // are expensive to create, and no unused threads shown in the debugger. + ThreadPool(); + + // Instantiates a thread pool with min(MaxNumThreadsAvailable, num_threads) + // number of threads. + explicit ThreadPool(int num_threads); + + // Signals the workers to stop and waits for them to finish any tasks that + // have been scheduled. + ~ThreadPool(); + + // Resizes the thread pool if it is currently less than the requested number + // of threads. The thread pool will be resized to min(MaxNumThreadsAvailable, + // num_threads) number of threads. Resize does not support reducing the + // thread pool size. If a smaller number of threads is requested, the thread + // pool remains the same size. The thread pool is reused within Ceres with + // different number of threads, and we need to ensure we can support the + // largest number of threads requested. It is safe to resize the thread pool + // while the workers are executing tasks, and the resizing is guaranteed to + // complete upon return. + void Resize(int num_threads); + + // Adds a task to the queue and wakes up a blocked thread. If the thread pool + // size is greater than zero, then the task will be executed by a currently + // idle thread or when a thread becomes available. If the thread pool has no + // threads, then the task will never be executed and the user should use + // Resize() to create a non-empty thread pool. + void AddTask(const std::function<void()>& func); + + // Returns the current size of the thread pool. + int Size(); + + private: + // Main loop for the threads which blocks on the task queue until work becomes + // available. It will return if and only if Stop has been called. + void ThreadMainLoop(); + + // Signal all the threads to stop. It does not block until the threads are + // finished. + void Stop(); + + // The queue that stores the units of work available for the thread pool. The + // task queue maintains its own thread safety. + ConcurrentQueue<std::function<void()>> task_queue_; + std::vector<std::thread> thread_pool_; + std::mutex thread_pool_mutex_; +}; + +} // namespace internal +} // namespace ceres + +#endif // CERES_INTERNAL_THREAD_POOL_H_ |