ThreadPool.h

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/*
GRT MIT License
Copyright (c) <2012> <Nicholas Gillian, Media Lab, MIT>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
and associated documentation files (the "Software"), to deal in the Software without restriction, 
including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, 
and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, 
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial 
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT 
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#ifndef GRT_THREAD_POOL_HEADER
#define GRT_THREAD_POOL_HEADER

//Include the common C++ headers
#include <vector>
#include <queue>
#include <stdexcept>

#ifdef GRT_CXX11_ENABLED
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#endif //GRT_CXX11_ENABLED

#include "GRTTypedefs.h"

GRT_BEGIN_NAMESPACE
    
class GRT_API ThreadPool {
public:
    
    ThreadPool();
    
    ThreadPool(const unsigned int numThreads);
    
    ~ThreadPool();

#ifdef GRT_CXX11_ENABLED

    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args) -> std::future< typename std::result_of<F(Args...) >::type>;
#endif //GRT_CXX11_ENABLED

    static unsigned int getThreadPoolSize();
    
    static bool setThreadPoolSize( const unsigned int threadPoolSize );
    
protected:
#ifdef GRT_CXX11_ENABLED
    void launchThreads(const unsigned int threads);
    
    std::vector< std::thread > workers;
    std::queue< std::function<void()> > tasks;
    
    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    std::atomic< bool > stop;
    
    static std::atomic< unsigned int > threadPoolSize;
#endif //GRT_CXX11_ENABLED
};
    
#ifdef GRT_CXX11_ENABLED
// This function adds a new work item (func) to the thread pool
template<class F, class... Args> auto ThreadPool::enqueue(F&& func, Args&&... args) -> std::future<typename std::result_of<F(Args...)>::type>
{
    //Get a shortcut to the return type of the input function
    using return_type = typename std::result_of< F(Args...) >::type;
    
    auto task = std::make_shared< std::packaged_task< return_type() > >( std::bind(std::forward<F>( func ), std::forward<Args>(args)...) );
    
    std::future< return_type > res = task->get_future();
    {
        std::unique_lock< std::mutex > lock( queue_mutex );
        
        // don't allow enqueueing after stopping the pool
        if( stop )
            throw std::runtime_error("enqueue on stopped ThreadPool");
        
        tasks.emplace( [task](){ (*task)(); } );
    }
    condition.notify_one();
    return res;
}
#endif //GRT_CXX11_ENABLED
    
GRT_END_NAMESPACE

#endif //GRT_THREAD_POOL_HEADER