ClickHouse/libs/libcommon/src/ThreadPool.cpp

#include <common/ThreadPool.h>
#include <iostream>


ThreadPool::ThreadPool(size_t m_size)
    : m_size(m_size)
{
    threads.reserve(m_size);
    for (size_t i = 0; i < m_size; ++i)
        threads.emplace_back([this] { worker(); });
}

void ThreadPool::schedule(Job job)
{
    {
        std::unique_lock<std::mutex> lock(mutex);
        has_free_thread.wait(lock, [this] { return active_jobs < m_size || shutdown; });
        if (shutdown)
            return;

        jobs.push(std::move(job));
        ++active_jobs;
    }
    has_new_job_or_shutdown.notify_one();
}

void ThreadPool::wait()
{
    {
        std::unique_lock<std::mutex> lock(mutex);
        has_free_thread.wait(lock, [this] { return active_jobs == 0; });

        if (first_exception)
        {
            std::exception_ptr exception;
            std::swap(exception, first_exception);
            std::rethrow_exception(exception);
        }
    }
}

ThreadPool::~ThreadPool()
{
    {
        std::unique_lock<std::mutex> lock(mutex);
        shutdown = true;
    }

    has_new_job_or_shutdown.notify_all();

    for (auto & thread : threads)
        thread.join();
}

size_t ThreadPool::active() const
{
    std::unique_lock<std::mutex> lock(mutex);
    return active_jobs;
}


void ThreadPool::worker()
{
    while (true)
    {
        Job job;
        bool need_shutdown = false;

        {
            std::unique_lock<std::mutex> lock(mutex);
            has_new_job_or_shutdown.wait(lock, [this] { return shutdown || !jobs.empty(); });
            need_shutdown = shutdown;

            if (!jobs.empty())
            {
                job = std::move(jobs.front());
                jobs.pop();
            }
            else
            {
                return;
            }
        }

        if (!need_shutdown)
        {
            try
            {
                job();
            }
            catch (...)
            {
                {
                    std::unique_lock<std::mutex> lock(mutex);
                    if (!first_exception)
                        first_exception = std::current_exception();
                    shutdown = true;
                    --active_jobs;
                }
                has_free_thread.notify_all();
                has_new_job_or_shutdown.notify_all();
                return;
            }
        }

        {
            std::unique_lock<std::mutex> lock(mutex);
            --active_jobs;
        }

        has_free_thread.notify_all();
    }
}