| // 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" |
| #include "ceres/internal/export.h" |
| |
| namespace ceres::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 CERES_NO_EXPORT 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 ceres::internal |
| |
| #endif // CERES_INTERNAL_THREAD_POOL_H_ |