threadpool.h

/*
BSD 3-Clause License

Copyright (c) 2020, Intel Corporation
All rights reserved.

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modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
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* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
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  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

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 HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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*/

#pragma once

#include "debug.h"

#include <thread>
#include <future>
#include <functional>
#include <mutex>
#include <condition_variable>
#include <queue>

namespace pcm {

class Work {
public:
    Work() {}
    virtual ~Work() {}
    virtual void execute() = 0;
};

template<class ReturnType>
class LambdaJob : public Work {
public:
    template<class F, class ... Args>
    LambdaJob( F&& f, Args&& ... args )
        //: task_( std::forward<F>(f)(std::forward<Args>( args )... ) ) {
        : task_(std::bind( f, args... ) ) {
    }

    virtual void execute() override {
        task_();
    }

    std::future<ReturnType> getFuture() {
        return task_.get_future();
    }

private:
    std::packaged_task<ReturnType()> task_;
};

class WorkQueue;

class ThreadPool {
private:
    ThreadPool( const int n ) {
        for ( int i = 0; i < n; ++i )
            addThread();
    }

    ThreadPool( ThreadPool const& ) = delete;

public:
    ~ThreadPool() {
        for ( size_t i = 0; i < threads_.size(); ++i )
            addWork( nullptr );
        for ( size_t i = 0; i < threads_.size(); ++i )
            threads_[i].join();
        threads_.clear();
    }

public:
    static ThreadPool& getInstance() {
        static ThreadPool tp_(64);
        return tp_;
    }

    void addWork( Work* w ) {
        DBG( 3, "WQ: Adding work" );
        std::lock_guard<std::mutex> lg( qMutex_ );
        workQ_.push( w );
        queueCV_.notify_one();
        DBG( 3, "WQ: Work available" );
    }

    Work* retrieveWork() {
        DBG( 3, "WQ: Retrieving work" );
        std::unique_lock<std::mutex> lock( qMutex_ );
        queueCV_.wait( lock, [this]{ return !workQ_.empty(); } );
        Work* w = workQ_.front();
        workQ_.pop();
        lock.unlock();
        DBG( 3, "WQ: Work retrieved" );

        return w;
    }

private:
    void addThread() {
        threads_.push_back( std::thread( std::bind( &this->execute, this ) ) );
    }

    // Executes work items from a std::thread, do not call manually
    static void execute( ThreadPool* );

private:
    std::vector<std::thread> threads_;
    std::queue<Work*> workQ_;
    std::mutex qMutex_;
    std::condition_variable queueCV_;
};

class WorkQueue {
public:
    WorkQueue() : tp_( ThreadPool::getInstance() ), workProcessed_(0) {}
    WorkQueue( WorkQueue const& ) = delete;
    ~WorkQueue() = default;

    // Just forwarding to the threadpool
    void addWork( Work* w ) {
        ++workProcessed_;
        tp_.addWork( w );
    }

private:
    ThreadPool& tp_;
    size_t workProcessed_;
};

} // namespace pcm