text: //
  // detail/epoll_reactor.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  
  #ifndef BOOST_ASIO_DETAIL_EPOLL_REACTOR_HPP
  #define BOOST_ASIO_DETAIL_EPOLL_REACTOR_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include <boost/asio/detail/config.hpp>
  
  #if defined(BOOST_ASIO_HAS_EPOLL)
  
  #include <boost/asio/detail/atomic_count.hpp>
  #include <boost/asio/detail/conditionally_enabled_mutex.hpp>
  #include <boost/asio/detail/limits.hpp>
  #include <boost/asio/detail/object_pool.hpp>
  #include <boost/asio/detail/op_queue.hpp>
  #include <boost/asio/detail/reactor_op.hpp>
  #include <boost/asio/detail/select_interrupter.hpp>
  #include <boost/asio/detail/socket_types.hpp>
  #include <boost/asio/detail/timer_queue_base.hpp>
  #include <boost/asio/detail/timer_queue_set.hpp>
  #include <boost/asio/detail/wait_op.hpp>
  #include <boost/asio/execution_context.hpp>
  
  #if defined(BOOST_ASIO_HAS_TIMERFD)
  # include <sys/timerfd.h>
  #endif // defined(BOOST_ASIO_HAS_TIMERFD)
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  namespace detail {
  
  class epoll_reactor
    : public execution_context_service_base<epoll_reactor>
  {
  private:
    // The mutex type used by this reactor.
    typedef conditionally_enabled_mutex mutex;
  
  public:
    enum op_types { read_op = 0, write_op = 1,
      connect_op = 1, except_op = 2, max_ops = 3 };
  
    // Per-descriptor queues.
    class descriptor_state : operation
    {
      friend class epoll_reactor;
      friend class object_pool_access;
  
      descriptor_state* next_;
      descriptor_state* prev_;
  
      mutex mutex_;
      epoll_reactor* reactor_;
      int descriptor_;
      uint32_t registered_events_;
      op_queue<reactor_op> op_queue_[max_ops];
      bool try_speculative_[max_ops];
      bool shutdown_;
  
      BOOST_ASIO_DECL descriptor_state(bool locking);
      void set_ready_events(uint32_t events) { task_result_ = events; }
      void add_ready_events(uint32_t events) { task_result_ |= events; }
      BOOST_ASIO_DECL operation* perform_io(uint32_t events);
      BOOST_ASIO_DECL static void do_complete(
          void* owner, operation* base,
          const boost::system::error_code& ec, std::size_t bytes_transferred);
    };
  
    // Per-descriptor data.
    typedef descriptor_state* per_descriptor_data;
  
    // Constructor.
    BOOST_ASIO_DECL epoll_reactor(boost::asio::execution_context& ctx);
  
    // Destructor.
    BOOST_ASIO_DECL ~epoll_reactor();
  
    // Destroy all user-defined handler objects owned by the service.
    BOOST_ASIO_DECL void shutdown();
  
    // Recreate internal descriptors following a fork.
    BOOST_ASIO_DECL void notify_fork(
        boost::asio::execution_context::fork_event fork_ev);
  
    // Initialise the task.
    BOOST_ASIO_DECL void init_task();
  
    // Register a socket with the reactor. Returns 0 on success, system error
    // code on failure.
    BOOST_ASIO_DECL int register_descriptor(socket_type descriptor,
        per_descriptor_data& descriptor_data);
  
    // Register a descriptor with an associated single operation. Returns 0 on
    // success, system error code on failure.
    BOOST_ASIO_DECL int register_internal_descriptor(
        int op_type, socket_type descriptor,
        per_descriptor_data& descriptor_data, reactor_op* op);
  
    // Move descriptor registration from one descriptor_data object to another.
    BOOST_ASIO_DECL void move_descriptor(socket_type descriptor,
        per_descriptor_data& target_descriptor_data,
        per_descriptor_data& source_descriptor_data);
  
    // Post a reactor operation for immediate completion.
    void post_immediate_completion(reactor_op* op, bool is_continuation)
    {
      scheduler_.post_immediate_completion(op, is_continuation);
    }
  
    // Start a new operation. The reactor operation will be performed when the
    // given descriptor is flagged as ready, or an error has occurred.
    BOOST_ASIO_DECL void start_op(int op_type, socket_type descriptor,
        per_descriptor_data& descriptor_data, reactor_op* op,
        bool is_continuation, bool allow_speculative);
  
    // Cancel all operations associated with the given descriptor. The
    // handlers associated with the descriptor will be invoked with the
    // operation_aborted error.
    BOOST_ASIO_DECL void cancel_ops(socket_type descriptor,
        per_descriptor_data& descriptor_data);
  
    // Cancel any operations that are running against the descriptor and remove
    // its registration from the reactor. The reactor resources associated with
    // the descriptor must be released by calling cleanup_descriptor_data.
    BOOST_ASIO_DECL void deregister_descriptor(socket_type descriptor,
        per_descriptor_data& descriptor_data, bool closing);
  
    // Remove the descriptor's registration from the reactor. The reactor
    // resources associated with the descriptor must be released by calling
    // cleanup_descriptor_data.
    BOOST_ASIO_DECL void deregister_internal_descriptor(
        socket_type descriptor, per_descriptor_data& descriptor_data);
  
    // Perform any post-deregistration cleanup tasks associated with the
    // descriptor data.
    BOOST_ASIO_DECL void cleanup_descriptor_data(
        per_descriptor_data& descriptor_data);
  
    // Add a new timer queue to the reactor.
    template <typename Time_Traits>
    void add_timer_queue(timer_queue<Time_Traits>& timer_queue);
  
    // Remove a timer queue from the reactor.
    template <typename Time_Traits>
    void remove_timer_queue(timer_queue<Time_Traits>& timer_queue);
  
    // Schedule a new operation in the given timer queue to expire at the
    // specified absolute time.
    template <typename Time_Traits>
    void schedule_timer(timer_queue<Time_Traits>& queue,
        const typename Time_Traits::time_type& time,
        typename timer_queue<Time_Traits>::per_timer_data& timer, wait_op* op);
  
    // Cancel the timer operations associated with the given token. Returns the
    // number of operations that have been posted or dispatched.
    template <typename Time_Traits>
    std::size_t cancel_timer(timer_queue<Time_Traits>& queue,
        typename timer_queue<Time_Traits>::per_timer_data& timer,
        std::size_t max_cancelled = (std::numeric_limits<std::size_t>::max)());
  
    // Move the timer operations associated with the given timer.
    template <typename Time_Traits>
    void move_timer(timer_queue<Time_Traits>& queue,
        typename timer_queue<Time_Traits>::per_timer_data& target,
        typename timer_queue<Time_Traits>::per_timer_data& source);
  
    // Run epoll once until interrupted or events are ready to be dispatched.
    BOOST_ASIO_DECL void run(long usec, op_queue<operation>& ops);
  
    // Interrupt the select loop.
    BOOST_ASIO_DECL void interrupt();
  
  private:
    // The hint to pass to epoll_create to size its data structures.
    enum { epoll_size = 20000 };
  
    // Create the epoll file descriptor. Throws an exception if the descriptor
    // cannot be created.
    BOOST_ASIO_DECL static int do_epoll_create();
  
    // Create the timerfd file descriptor. Does not throw.
    BOOST_ASIO_DECL static int do_timerfd_create();
  
    // Allocate a new descriptor state object.
    BOOST_ASIO_DECL descriptor_state* allocate_descriptor_state();
  
    // Free an existing descriptor state object.
    BOOST_ASIO_DECL void free_descriptor_state(descriptor_state* s);
  
    // Helper function to add a new timer queue.
    BOOST_ASIO_DECL void do_add_timer_queue(timer_queue_base& queue);
  
    // Helper function to remove a timer queue.
    BOOST_ASIO_DECL void do_remove_timer_queue(timer_queue_base& queue);
  
    // Called to recalculate and update the timeout.
    BOOST_ASIO_DECL void update_timeout();
  
    // Get the timeout value for the epoll_wait call. The timeout value is
    // returned as a number of milliseconds. A return value of -1 indicates
    // that epoll_wait should block indefinitely.
    BOOST_ASIO_DECL int get_timeout(int msec);
  
  #if defined(BOOST_ASIO_HAS_TIMERFD)
    // Get the timeout value for the timer descriptor. The return value is the
    // flag argument to be used when calling timerfd_settime.
    BOOST_ASIO_DECL int get_timeout(itimerspec& ts);
  #endif // defined(BOOST_ASIO_HAS_TIMERFD)
  
    // The scheduler implementation used to post completions.
    scheduler& scheduler_;
  
    // Mutex to protect access to internal data.
    mutex mutex_;
  
    // The interrupter is used to break a blocking epoll_wait call.
    select_interrupter interrupter_;
  
    // The epoll file descriptor.
    int epoll_fd_;
  
    // The timer file descriptor.
    int timer_fd_;
  
    // The timer queues.
    timer_queue_set timer_queues_;
  
    // Whether the service has been shut down.
    bool shutdown_;
  
    // Mutex to protect access to the registered descriptors.
    mutex registered_descriptors_mutex_;
  
    // Keep track of all registered descriptors.
    object_pool<descriptor_state> registered_descriptors_;
  
    // Helper class to do post-perform_io cleanup.
    struct perform_io_cleanup_on_block_exit;
    friend struct perform_io_cleanup_on_block_exit;
  };
  
  } // namespace detail
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #include <boost/asio/detail/impl/epoll_reactor.hpp>
  #if defined(BOOST_ASIO_HEADER_ONLY)
  # include <boost/asio/detail/impl/epoll_reactor.ipp>
  #endif // defined(BOOST_ASIO_HEADER_ONLY)
  
  #endif // defined(BOOST_ASIO_HAS_EPOLL)
  
  #endif // BOOST_ASIO_DETAIL_EPOLL_REACTOR_HPP
  