thehub/libs/utils/WorkerThreads.h

/*
 * This file is part of the Flowee project
 * Copyright (C) 2018-2025 Tom Zander <tom@flowee.org>
 *
 * 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 3 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, see <http://www.gnu.org/licenses/>.
 */
#ifndef FLOWEE_WORKERTHREADS_H
#define FLOWEE_WORKERTHREADS_H

#include <boost/asio/io_context.hpp>
#include <boost/asio/executor_work_guard.hpp>
#include <boost/thread.hpp>

/**
 * This is a class that spawns a series of threads where jobs can be run on.
 * The WorkerThreads class starts a list of threads based on the amount of
 * cores detected on the hardware, each thread will then be run to become an
 * event-queue based on the boost asio primitives.
 *
 * Notice that the threads catch exceptions and continue the next event
 * in the event-queue after logging a generic message.
 */
class WorkerThreads
{
public:
    /**
     * Create all threads and start them.
     * @param threadCount the number of threads to start, or -1 to use the hardware concurrency amount.
     */
    WorkerThreads(int threadCount = -1);
    ~WorkerThreads();

    /// request a peaceful shutdown of the threads. (thread-safe)
    void stopThreads();
    /// blocking wait until all threads finished.
    void joinAll();

    /// Return a ref to the ioContext owned by this WorkerThreads.
    boost::asio::io_context& ioContext() const;

    /**
     * Wrapper function that allows users to create a thread on our thread-group.
     */
    template<typename F>
    boost::thread* createNewThread(F threadfunc) {
        return m_threads.create_thread(threadfunc);
    }

protected:
    /// only called from constructor. Useful in unit tests.
    void startThreads(int threadCount = -1);

private:
    std::shared_ptr<boost::asio::io_context> m_context;
    // work around weird template shit from boost that makes it impossible to reuse
    // the same stack defined item multiple times.
    struct Work {
        Work(const std::shared_ptr<boost::asio::io_context> &context);
        boost::asio::executor_work_guard<boost::asio::io_context::executor_type> work;
    };
    std::unique_ptr<Work> m_work;
    boost::thread_group m_threads;
};

#endif