/*
Copyright (c) 2015, Andreas F. Borchert
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. 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.
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.
*/
/*
This header-only C++ package provides hpc::mt::thread_pool which
assigns incoming tasks to a fixed number of threads. The template
parameter determines the return type of a task.
Following methods are supported:
* ThreadPool(unsigned int nofthreads)
construct thread pool with the given number of threads
* ~ThreadPool()
the destructor waits for all threads to finish
* void join()
wait for all threads to finish
* void terminate()
request a speedy termination, i.e. submitted but not yet assigned
tasks remain undone; threads that wait for the corresponding futures
will see broken promises
* std::future<T> submit(F task_function)
submit a task which is to be executed by one of the threads
of the pool; the future objects allows to synchronize with
the completion of the task and to receive the return value
of the submitted task
*/
#ifndef HPC_MT_THREAD_POOL_H
#define HPC_MT_THREAD_POOL_H 1
#include <condition_variable>
#include <future>
#include <list>
#include <mutex>
#include <thread>
#include <type_traits>
#include <utility>
#include <vector>
namespace hpc { namespace mt {
#if defined(__GNUC__) && __GNUC__ == 4 && (__GNUC_MINOR__ == 7 || __GNUC__MINOR__ == 8)
/* GCC 4.7.x and early releases of 4.8.x have a serious bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53921
the bug arises when lambda expressions are used within templated classes
that refer to members of that class (implicitly through this);
the workaround is to use "this->" explicitly
*/
template<typename T>
class ThreadPool {
public:
ThreadPool(unsigned int nofthreads) :
threads(nofthreads), active(0),
joining(false), terminating(false) {
for (auto& t: threads) {
t = std::thread([=]() mutable -> void {
for (;;) {
std::packaged_task<T()> task;
/* fetch next task, if there is any */
{
std::unique_lock<std::mutex> lock(this->mutex);
while (!this->terminating &&
this->tasks.empty() &&
(this->active > 0 || !this->joining)) {
this->cv.wait(lock);
}
if (this->terminating || this->tasks.empty()) {
this->terminating = true;
break; /* all done */
}
task = std::move(this->tasks.front());
this->tasks.pop_front();
++this->active;
}
/* process task */
task();
/* decrement number of active threads */
{
std::unique_lock<std::mutex> lock(this->mutex);
--this->active;
}
}
this->cv.notify_all();
});
}
}
~ThreadPool() {
join();
}
void join() {
if (!joining && !terminating) {
std::unique_lock<std::mutex> lock(mutex);
joining = true;
}
cv.notify_all();
for (auto& t: threads) if (t.joinable()) t.join();
}
void terminate() {
{
std::unique_lock<std::mutex> lock(mutex);
terminating = true;
/* we make sure that all promises left are considered broken
by emptying the list of remaining tasks;
if we do not do it now, the waiting threads would
have to wait until this object is destructed
*/
tasks.empty();
}
cv.notify_all();
}
template<typename F>
std::future<T> submit(F task_function) {
std::packaged_task<T()> task(task_function);
std::future<T> result = task.get_future();
std::lock_guard<std::mutex> lock(mutex);
tasks.push_back(std::move(task));
cv.notify_one();
return result;
}
private:
std::vector<std::thread> threads;
std::mutex mutex;
std::list<std::packaged_task<T()>> tasks;
std::condition_variable cv;
unsigned int active;
bool joining;
bool terminating;
};
#else
template<typename T>
class ThreadPool {
public:
ThreadPool(unsigned int nofthreads) :
threads(nofthreads), active(0),
joining(false), terminating(false) {
for (auto& t: threads) {
t = std::thread([=]() mutable -> void {
for (;;) {
std::packaged_task<T()> task;
/* fetch next task, if there is any */
{
std::unique_lock<std::mutex> lock(mutex);
while (!terminating &&
tasks.empty() &&
(active > 0 || !joining)) {
cv.wait(lock);
}
if (terminating || tasks.empty()) {
terminating = true;
break; /* all done */
}
task = std::move(tasks.front());
tasks.pop_front();
++active;
}
/* process task */
task();
/* decrement number of active threads */
{
std::unique_lock<std::mutex> lock(mutex);
--active;
}
}
cv.notify_all();
});
}
}
~ThreadPool() {
join();
}
void join() {
if (!joining && !terminating) {
std::unique_lock<std::mutex> lock(mutex);
joining = true;
}
cv.notify_all();
for (auto& t: threads) if (t.joinable()) t.join();
}
void terminate() {
{
std::unique_lock<std::mutex> lock(mutex);
terminating = true;
/* we make sure that all promises left are considered broken
by emptying the list of remaining tasks;
if we do not do it now, the waiting threads would
have to wait until this object is destructed
*/
tasks.empty();
}
cv.notify_all();
}
template<typename F>
std::future<T> submit(F task_function) {
std::packaged_task<T()> task(task_function);
std::future<T> result = task.get_future();
std::lock_guard<std::mutex> lock(mutex);
tasks.push_back(std::move(task));
cv.notify_one();
return result;
}
private:
std::vector<std::thread> threads;
std::mutex mutex;
std::list<std::packaged_task<T()>> tasks;
std::condition_variable cv;
unsigned int active;
bool joining;
bool terminating;
};
#endif
} } // namespaces mt and hpc
#endif