async_logger.h

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//
// Copyright(c) 2015 Gabi Melman.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
//

#pragma once

// Very fast asynchronous logger (millions of logs per second on an average
// desktop)
// Uses pre allocated lockfree queue for maximum throughput even under large
// number of threads.
// Creates a single back thread to pop messages from the queue and log them.
//
// Upon each log write the logger:
//    1. Checks if its log level is enough to log the message
//    2. Push a new copy of the message to a queue (or block the caller until
//    space is available in the queue)
//    3. will throw spdlog_ex upon log exceptions
// Upon destruction, logs all remaining messages in the queue before
// destructing..

#include "spdlog/common.h"
#include "spdlog/logger.h"

#include <chrono>
#include <memory>
#include <string>

namespace spdlog {

// Async overflow policy - block by default.
enum class async_overflow_policy
{
    block,         // Block until message can be enqueued
    overrun_oldest // Discard oldest message in the queue if full when trying to
                   // add new item.
};

namespace details {
class thread_pool;
}

class async_logger final : public std::enable_shared_from_this<async_logger>, public logger
{
    friend class details::thread_pool;

public:
    template<typename It>
    async_logger(std::string logger_name, It begin, It end, std::weak_ptr<details::thread_pool> tp,
        async_overflow_policy overflow_policy = async_overflow_policy::block);

    async_logger(std::string logger_name, sinks_init_list sinks_list, std::weak_ptr<details::thread_pool> tp,
        async_overflow_policy overflow_policy = async_overflow_policy::block);

    async_logger(std::string logger_name, sink_ptr single_sink, std::weak_ptr<details::thread_pool> tp,
        async_overflow_policy overflow_policy = async_overflow_policy::block);

    std::shared_ptr<logger> clone(std::string new_name) override;

protected:
    void sink_it_(details::log_msg &msg) override;
    void flush_() override;

    void backend_log_(const details::log_msg &incoming_log_msg);
    void backend_flush_();

private:
    std::weak_ptr<details::thread_pool> thread_pool_;
    async_overflow_policy overflow_policy_;
};
} // namespace spdlog

#include "details/async_logger_impl.h"