// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "sdk_util/thread_pool.h"
#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include "sdk_util/auto_lock.h"
namespace sdk_util {
#ifdef __APPLE__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
#endif
// Initializes mutex, semaphores and a pool of threads. If 0 is passed for
// num_threads, all work will be performed on the dispatch thread.
ThreadPool::ThreadPool(int num_threads)
: threads_(NULL), counter_(0), num_threads_(num_threads), exiting_(false),
user_data_(NULL), user_work_function_(NULL) {
if (num_threads_ > 0) {
int status;
status = sem_init(&work_sem_, 0, 0);
if (-1 == status) {
fprintf(stderr, "Failed to initialize semaphore!\n");
exit(-1);
}
status = sem_init(&done_sem_, 0, 0);
if (-1 == status) {
fprintf(stderr, "Failed to initialize semaphore!\n");
exit(-1);
}
threads_ = new pthread_t[num_threads_];
for (int i = 0; i < num_threads_; i++) {
status = pthread_create(&threads_[i], NULL, WorkerThreadEntry, this);
if (0 != status) {
fprintf(stderr, "Failed to create thread!\n");
exit(-1);
}
}
}
}
// Post exit request, wait for all threads to join, and cleanup.
ThreadPool::~ThreadPool() {
if (num_threads_ > 0) {
PostExitAndJoinAll();
delete[] threads_;
sem_destroy(&done_sem_);
sem_destroy(&work_sem_);
}
}
// Setup work parameters. This function is called from the dispatch thread,
// when all worker threads are sleeping.
void ThreadPool::Setup(int counter, WorkFunction work, void *data) {
counter_ = counter;
user_work_function_ = work;
user_data_ = data;
}
// Return decremented task counter. This function
// can be called from multiple threads at any given time.
int ThreadPool::DecCounter() {
return AtomicAddFetch(&counter_, -1);
}
// Set exit flag, post and join all the threads in the pool. This function is
// called only from the dispatch thread, and only when all worker threads are
// sleeping.
void ThreadPool::PostExitAndJoinAll() {
exiting_ = true;
// Wake up all the sleeping worker threads.
for (int i = 0; i < num_threads_; ++i)
sem_post(&work_sem_);
void* retval;
for (int i = 0; i < num_threads_; ++i)
pthread_join(threads_[i], &retval);
}
// Main work loop - one for each worker thread.
void ThreadPool::WorkLoop() {
while (true) {
// Wait for work. If no work is available, this thread will sleep here.
sem_wait(&work_sem_);
if (exiting_) break;
while (true) {
// Grab a task index to work on from the counter.
int task_index = DecCounter();
if (task_index < 0)
break;
user_work_function_(task_index, user_data_);
}
// Post to dispatch thread work is done.
sem_post(&done_sem_);
}
}
// pthread entry point for a worker thread.
void* ThreadPool::WorkerThreadEntry(void* thiz) {
static_cast<ThreadPool*>(thiz)->WorkLoop();
return NULL;
}
// DispatchMany() will dispatch a set of tasks across worker threads.
// Note: This function will block until all work has completed.
void ThreadPool::DispatchMany(int num_tasks, WorkFunction work, void* data) {
// On entry, all worker threads are sleeping.
Setup(num_tasks, work, data);
// Wake up the worker threads & have them process tasks.
for (int i = 0; i < num_threads_; i++)
sem_post(&work_sem_);
// Worker threads are now awake and busy.
// This dispatch thread will now sleep-wait for the worker threads to finish.
for (int i = 0; i < num_threads_; i++)
sem_wait(&done_sem_);
// On exit, all tasks are done and all worker threads are sleeping again.
}
#ifdef __APPLE__
#pragma clang diagnostic pop
#endif
// DispatchHere will dispatch all tasks on this thread.
void ThreadPool::DispatchHere(int num_tasks, WorkFunction work, void* data) {
for (int i = 0; i < num_tasks; i++)
work(i, data);
}
// Dispatch() will invoke the user supplied work function across
// one or more threads for each task.
// Note: This function will block until all work has completed.
void ThreadPool::Dispatch(int num_tasks, WorkFunction work, void* data) {
if (num_threads_ > 0)
DispatchMany(num_tasks, work, data);
else
DispatchHere(num_tasks, work, data);
}
} // namespace sdk_util
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