furnace/src/engine/workPool.h

/**
 * Furnace Tracker - multi-system chiptune tracker
 * Copyright (C) 2021-2023 tildearrow and contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#ifndef _WORKPOOL_H
#define _WORKPOOL_H

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

#include "fixedQueue.h"

class DivWorkPool;

struct DivPendingTask {
  std::function<void(void*)> func;
  void* funcArg;
  DivPendingTask(std::function<void(void*)> f, void* arg):
    func(f),
    funcArg(arg) {}
  DivPendingTask():
    func(NULL),
    funcArg(NULL) {}
};

struct DivWorkThread {
  DivWorkPool* parent;
  std::mutex lock;
  std::mutex selfLock;
  std::thread* thread;
  std::condition_variable notify;
  FixedQueue<DivPendingTask,32> tasks;
  std::atomic<bool> isBusy;
  bool terminate;

  void run();
  bool assign(const std::function<void(void*)>& what, void* arg);
  void wait();
  bool busy();
  void finish();

  void init(DivWorkPool* p);
  DivWorkThread():
    parent(NULL),
    isBusy(false),
    terminate(false) {}
};

/**
 * this class provides an implementation of a "thread pool" for executing tasks in parallel.
 * it is highly recommended to use `new` when allocating a DivWorkPool.
 */
class DivWorkPool {
  bool threaded;
  unsigned int count;
  unsigned int pos;
  DivWorkThread* workThreads;
  public:
    std::promise<void> notify;
    std::atomic<int> busyCount;
    
    /**
     * push a new job to this work pool.
     * if all work threads are busy, this will block until one is free.
     */
    void push(const std::function<void(void*)>& what, void* arg);
    
    /**
     * check whether this work pool is busy.
     */
    bool busy();

    /**
     * wait for all work threads to finish.
     */
    void wait();

    DivWorkPool(unsigned int threads=0);
    ~DivWorkPool();
};

#endif