text: //
  // Copyright(c) 2015 Gabi Melman.
  // Distributed under the MIT License (http://opensource.org/licenses/MIT)
  //
  #ifndef ABEL_LOG_ASYNC_LOGGER_H_
  #define ABEL_LOG_ASYNC_LOGGER_H_
  
  // 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 log_ex upon log exceptions
  // Upon destruction, logs all remaining messages in the queue before
  // destructing..
  
  #include <abel/log/common.h>
  #include <abel/log/logger.h>
  
  #include <chrono>
  #include <memory>
  #include <string>
  
  namespace abel {
  namespace log {
  
  // 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 ABEL_INHERITANCE_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, const It &begin, const 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, 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);
  
  protected:
      void sink_it_ (details::log_msg &msg) override;
      void flush_ () override;
  
      void backend_log_ (details::log_msg &incoming_log_msg);
      void backend_flush_ ();
  
  private:
      std::weak_ptr<details::thread_pool> thread_pool_;
      async_overflow_policy overflow_policy_;
  };
  } //namespace log
  } // namespace abel
  
  #include "details/async_logger_impl.h"
  #endif //ABEL_LOG_ASYNC_LOGGER_H_
  