spdlog/include/spdlog/details/thread_pool.h

// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)

#pragma once

#include <spdlog/details/log_msg_buffer.h>
#include <spdlog/details/mpmc_blocking_q.h>
#include <spdlog/details/os.h>

#include <chrono>
#include <functional>
#include <memory>
#include <thread>
#include <vector>

namespace spdlog {
class async_logger;

namespace details {

using async_logger_ptr = std::shared_ptr<spdlog::async_logger>;

enum class async_msg_type { log, flush, terminate };

enum class async_msg_flush { not_synced, synced_flushed, synced_not_flushed };

// Async msg to move to/from the queue
// Movable only. should never be copied
struct async_msg : log_msg_buffer {
    async_msg_type msg_type{async_msg_type::log};
    async_logger_ptr worker_ptr;
    std::function<void(async_msg_flush)> flush_callback;

    async_msg() = default;
    ~async_msg() {
        if (flush_callback) {
            flush_callback(async_msg_flush::synced_not_flushed);
            flush_callback = nullptr;
        }
    }

    // should only be moved in or out of the queue..
    async_msg(const async_msg &) = delete;

    async_msg(async_msg &&other) SPDLOG_NOEXCEPT
        : log_msg_buffer(std::move(other)),
          msg_type(other.msg_type),
          worker_ptr(std::move(other.worker_ptr)),
          flush_callback(std::move(other.flush_callback)) {
        other.flush_callback = nullptr;
    }
    async_msg &operator=(async_msg &&other) SPDLOG_NOEXCEPT {
        *static_cast<log_msg_buffer *>(this) = static_cast<log_msg_buffer&&>(other);
        msg_type = other.msg_type;
        worker_ptr = std::move(other.worker_ptr);
        flush_callback = std::move(other.flush_callback);
        other.flush_callback = nullptr;
        return *this;
    }

    // construct from log_msg with given type
    async_msg(async_logger_ptr &&worker, async_msg_type the_type, const details::log_msg &m)
        : log_msg_buffer{m},
          msg_type{the_type},
          worker_ptr{std::move(worker)},
          flush_callback{} {}

    async_msg(async_logger_ptr &&worker, async_msg_type the_type)
        : log_msg_buffer{},
          msg_type{the_type},
          worker_ptr{std::move(worker)},
          flush_callback{} {}

    async_msg(async_logger_ptr &&worker, async_msg_type the_type, std::function<void(async_msg_flush)> &&callback)
        : log_msg_buffer{},
          msg_type{the_type},
          worker_ptr{std::move(worker)},
          flush_callback{std::move(callback)} {}

    explicit async_msg(async_msg_type the_type)
        : async_msg{nullptr, the_type} {}
};

class SPDLOG_API thread_pool {
public:
    using item_type = async_msg;
    using q_type = details::mpmc_blocking_queue<item_type>;

    thread_pool(size_t q_max_items,
                size_t threads_n,
                std::function<void()> on_thread_start,
                std::function<void()> on_thread_stop);
    thread_pool(size_t q_max_items, size_t threads_n, std::function<void()> on_thread_start);
    thread_pool(size_t q_max_items, size_t threads_n);

    // message all threads to terminate gracefully and join them
    ~thread_pool();

    thread_pool(const thread_pool &) = delete;
    thread_pool &operator=(thread_pool &&) = delete;

    void post_log(async_logger_ptr &&worker_ptr,
                  const details::log_msg &msg,
                  async_overflow_policy overflow_policy);
    void post_and_wait_for_flush(async_logger_ptr &&worker_ptr,
                                 async_overflow_policy overflow_policy);
    size_t overrun_counter();
    void reset_overrun_counter();
    size_t discard_counter();
    void reset_discard_counter();
    size_t queue_size();

private:
    q_type q_;

    std::vector<std::thread> threads_;

    void post_async_msg_(async_msg &&new_msg, async_overflow_policy overflow_policy);
    void worker_loop_();

    // process next message in the queue
    // return true if this thread should still be active (while no terminate msg
    // was received)
    bool process_next_msg_();
};

}  // namespace details
}  // namespace spdlog

#ifdef SPDLOG_HEADER_ONLY
    #include "thread_pool-inl.h"
#endif