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/*
Copyright 2018 Google Inc. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS-IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#ifndef RESONANCE_AUDIO_UTILS_TASK_THREAD_POOL_H_
#define RESONANCE_AUDIO_UTILS_TASK_THREAD_POOL_H_
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <functional>
#include <mutex>
#include <vector>
namespace vraudio {
class TaskThreadPool;
// A very basic thread pool for launching discrete encapsulated task functions
// on a configurable number of task threads. Note that this pool expects tasks
// to complete their work with no management by the pool itself. Any means of
// managing or terminating tasks must be designed into the task contexts and
// managed externally in a thread-safe way.
class TaskThreadPool {
friend class WorkerThread;
public:
// Type definition for task function which may be assigned to a |WorkerThread|
// in this pool. Note that tasks should be self-contained and not require
// communication with other tasks.
typedef std::function<void()> TaskClosure;
// Constructor.
//
TaskThreadPool();
~TaskThreadPool();
// Creates and initializes thread pool. This method blocks until all threads
// are loaded and initialized.
//
// @param num_worker_threads The number of worker threads to make available in
// the pool.
// @return true on success or if thread pool has been already started.
bool StartThreadPool(size_t num_worker_threads);
// Signals all |WorkerThread|s to stop and waits for completion.
void StopThreadPool();
// Waits until a |WorkerThread| becomes available. It is assumed that only a
// single thread will dispatch threads using this function, and therefore this
// function should not itself be considered thread safe.
//
// @return True if a |WorkerThread| is available.
bool WaitUntilWorkerBecomesAvailable();
// Executes a |TaskClosure| on a |WorkerThread|. It is assumed that only a
// signal thread will dispatch threads using this function, and therefore this
// function should not itself be considered thread safe.
//
// @param closure The client task which will begin execution if and when this
// function returns True.
// @return True if a |WorkerThread| is allocated to execute the closure
// function, false if no |WorkerThread| is available.
bool RunOnWorkerThread(TaskClosure closure);
// Query the number of |WorkerThread|s current available to do work.
size_t GetAvailableTaskThreadCount() const;
private:
// Forward declaration of |WorkerThread| class. See implementation file for
// class details.
class WorkerThread;
// Query whether the |TaskThreadPool| is active.
//
// @return True if the pool is still running.
bool IsPoolRunning();
// Signals to thread pool that a worker thread has become available for
// task assignment.
void SignalWorkerAvailable();
// Closure reusable task loop to be executed by each |WorkerThread|.
void WorkerLoopFunction();
// Task Loop executed by each worker thread.
void WorkerThreadLoop();
// Number of worker threads currently available to execute tasks.
std::atomic<int> num_worker_threads_available_;
// Control of all worker thread loops.
std::atomic<bool> is_pool_running_;
// Container of available worker threads, waiting to be used.
std::vector<WorkerThread> worker_threads_;
// Condition to indicate that a worker thread has become available.
std::condition_variable worker_available_condition_;
// Mutex for the worker thread available condition notification receiver.
std::mutex worker_available_mutex_;
};
} // namespace vraudio
#endif // RESONANCE_AUDIO_UTILS_TASK_THREAD_POOL_H_
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