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Merge branch 'thread_pool'
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@jeffreybarrick
jeffreybarrick committed Aug 7, 2020
2 parents 5e5b6f7 + 42c1845 commit c75d36e
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251 changes: 251 additions & 0 deletions src/c/breseq/libbreseq/ctpl_stl.h
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/*********************************************************
*
* Copyright (C) 2014 by Vitaliy Vitsentiy
*
* 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 __ctpl_stl_thread_pool_H__
#define __ctpl_stl_thread_pool_H__

#include <functional>
#include <thread>
#include <atomic>
#include <vector>
#include <memory>
#include <exception>
#include <future>
#include <mutex>
#include <queue>



// thread pool to run user's functors with signature
// ret func(int id, other_params)
// where id is the index of the thread that runs the functor
// ret is some return type


namespace ctpl {

namespace detail {
template <typename T>
class Queue {
public:
bool push(T const & value) {
std::unique_lock<std::mutex> lock(this->mutex);
this->q.push(value);
return true;
}
// deletes the retrieved element, do not use for non integral types
bool pop(T & v) {
std::unique_lock<std::mutex> lock(this->mutex);
if (this->q.empty())
return false;
v = this->q.front();
this->q.pop();
return true;
}
bool empty() {
std::unique_lock<std::mutex> lock(this->mutex);
return this->q.empty();
}
private:
std::queue<T> q;
std::mutex mutex;
};
}

class thread_pool {

public:

thread_pool() { this->init(); }
thread_pool(int nThreads) { this->init(); this->resize(nThreads); }

// the destructor waits for all the functions in the queue to be finished
~thread_pool() {
this->stop(true);
}

// get the number of running threads in the pool
int size() { return static_cast<int>(this->threads.size()); }

// number of idle threads
int n_idle() { return this->nWaiting; }
std::thread & get_thread(int i) { return *this->threads[i]; }

// change the number of threads in the pool
// should be called from one thread, otherwise be careful to not interleave, also with this->stop()
// nThreads must be >= 0
void resize(int nThreads) {
if (!this->isStop && !this->isDone) {
int oldNThreads = static_cast<int>(this->threads.size());
if (oldNThreads <= nThreads) { // if the number of threads is increased
this->threads.resize(nThreads);
this->flags.resize(nThreads);

for (int i = oldNThreads; i < nThreads; ++i) {
this->flags[i] = std::make_shared<std::atomic<bool>>(false);
this->set_thread(i);
}
}
else { // the number of threads is decreased
for (int i = oldNThreads - 1; i >= nThreads; --i) {
*this->flags[i] = true; // this thread will finish
this->threads[i]->detach();
}
{
// stop the detached threads that were waiting
std::unique_lock<std::mutex> lock(this->mutex);
this->cv.notify_all();
}
this->threads.resize(nThreads); // safe to delete because the threads are detached
this->flags.resize(nThreads); // safe to delete because the threads have copies of shared_ptr of the flags, not originals
}
}
}

// empty the queue
void clear_queue() {
std::function<void(int id)> * _f;
while (this->q.pop(_f))
delete _f; // empty the queue
}

// pops a functional wrapper to the original function
std::function<void(int)> pop() {
std::function<void(int id)> * _f = nullptr;
this->q.pop(_f);
std::unique_ptr<std::function<void(int id)>> func(_f); // at return, delete the function even if an exception occurred
std::function<void(int)> f;
if (_f)
f = *_f;
return f;
}

// wait for all computing threads to finish and stop all threads
// may be called asynchronously to not pause the calling thread while waiting
// if isWait == true, all the functions in the queue are run, otherwise the queue is cleared without running the functions
void stop(bool isWait = false) {
if (!isWait) {
if (this->isStop)
return;
this->isStop = true;
for (int i = 0, n = this->size(); i < n; ++i) {
*this->flags[i] = true; // command the threads to stop
}
this->clear_queue(); // empty the queue
}
else {
if (this->isDone || this->isStop)
return;
this->isDone = true; // give the waiting threads a command to finish
}
{
std::unique_lock<std::mutex> lock(this->mutex);
this->cv.notify_all(); // stop all waiting threads
}
for (int i = 0; i < static_cast<int>(this->threads.size()); ++i) { // wait for the computing threads to finish
if (this->threads[i]->joinable())
this->threads[i]->join();
}
// if there were no threads in the pool but some functors in the queue, the functors are not deleted by the threads
// therefore delete them here
this->clear_queue();
this->threads.clear();
this->flags.clear();
}

template<typename F, typename... Rest>
auto push(F && f, Rest&&... rest) ->std::future<decltype(f(0, rest...))> {
auto pck = std::make_shared<std::packaged_task<decltype(f(0, rest...))(int)>>(
std::bind(std::forward<F>(f), std::placeholders::_1, std::forward<Rest>(rest)...)
);
auto _f = new std::function<void(int id)>([pck](int id) {
(*pck)(id);
});
this->q.push(_f);
std::unique_lock<std::mutex> lock(this->mutex);
this->cv.notify_one();
return pck->get_future();
}

// run the user's function that excepts argument int - id of the running thread. returned value is templatized
// operator returns std::future, where the user can get the result and rethrow the catched exceptins
template<typename F>
auto push(F && f) ->std::future<decltype(f(0))> {
auto pck = std::make_shared<std::packaged_task<decltype(f(0))(int)>>(std::forward<F>(f));
auto _f = new std::function<void(int id)>([pck](int id) {
(*pck)(id);
});
this->q.push(_f);
std::unique_lock<std::mutex> lock(this->mutex);
this->cv.notify_one();
return pck->get_future();
}


private:

// deleted
thread_pool(const thread_pool &);// = delete;
thread_pool(thread_pool &&);// = delete;
thread_pool & operator=(const thread_pool &);// = delete;
thread_pool & operator=(thread_pool &&);// = delete;

void set_thread(int i) {
std::shared_ptr<std::atomic<bool>> flag(this->flags[i]); // a copy of the shared ptr to the flag
auto f = [this, i, flag/* a copy of the shared ptr to the flag */]() {
std::atomic<bool> & _flag = *flag;
std::function<void(int id)> * _f;
bool isPop = this->q.pop(_f);
while (true) {
while (isPop) { // if there is anything in the queue
std::unique_ptr<std::function<void(int id)>> func(_f); // at return, delete the function even if an exception occurred
(*_f)(i);
if (_flag)
return; // the thread is wanted to stop, return even if the queue is not empty yet
else
isPop = this->q.pop(_f);
}
// the queue is empty here, wait for the next command
std::unique_lock<std::mutex> lock(this->mutex);
++this->nWaiting;
this->cv.wait(lock, [this, &_f, &isPop, &_flag](){ isPop = this->q.pop(_f); return isPop || this->isDone || _flag; });
--this->nWaiting;
if (!isPop)
return; // if the queue is empty and this->isDone == true or *flag then return
}
};
this->threads[i].reset(new std::thread(f)); // compiler may not support std::make_unique()
}

void init() { this->nWaiting = 0; this->isStop = false; this->isDone = false; }

std::vector<std::unique_ptr<std::thread>> threads;
std::vector<std::shared_ptr<std::atomic<bool>>> flags;
detail::Queue<std::function<void(int id)> *> q;
std::atomic<bool> isDone;
std::atomic<bool> isStop;
std::atomic<int> nWaiting; // how many threads are waiting

std::mutex mutex;
std::condition_variable cv;
};

}

#endif // __ctpl_stl_thread_pool_H__

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