每个xxx_service都有一个implementation_type如上图所示，
./asio/detail/winrt_ssocket_service.hpp:50: struct implementation_type : base_implementation_type
./asio/detail/win_iocp_socket_service.hpp:109: struct implementation_type :
./asio/detail/reactive_socket_service.hpp:62: struct implementation_type :
./asio/detail/null_socket_service.hpp:48: struct implementation_type
./asio/detail/deadline_timer_service.hpp:56: struct implementation_type
这里主要说reactive_socket_service和deadline_timer_service下的implementation_type,
1)reactive_socket_service::implementation_type 信息如下：
1 struct implementation_type : 2 reactive_socket_service_base::base_implementation_type 3 { 4 // Default constructor. 5 implementation_type() 6 : protocol_(endpoint_type().protocol()) 7 { 8 } 9 10 // The protocol associated with the socket. 11 protocol_type protocol_; 12 };
其父类base_implementation_type信息如下：
1 struct base_implementation_type 2 { 3 // The native socket representation. 4 socket_type socket_; 5 6 // The current state of the socket. 7 socket_ops::state_type state_; 8 9 // Per-descriptor data used by the reactor. 10 reactor::per_descriptor_data reactor_data_; 11 };
其中per_descriptor_data信息如下：
1 // Per-descriptor queues. 2 class descriptor_state : operation 3 { 4 friend class epoll_reactor; 5 friend class object_pool_access; 6 7 descriptor_state* next_; 8 descriptor_state* prev_; 9 10 mutex mutex_; 11 epoll_reactor* reactor_; 12 int descriptor_; 13 uint32_t registered_events_; 14 op_queue<reactor_op> op_queue_[max_ops]; 15 bool shutdown_; 16 17 BOOST_ASIO_DECL descriptor_state(); 18 void set_ready_events(uint32_t events) { task_result_ = events; } 19 BOOST_ASIO_DECL operation* perform_io(uint32_t events); 20 BOOST_ASIO_DECL static void do_complete( 21 io_service_impl* owner, operation* base, 22 const boost::system::error_code& ec, std::size_t bytes_transferred); 23 };
// Per-descriptor data.
typedef descriptor_state* per_descriptor_data;
主要关心的是epoll_wait回调函数do_complete和io任务队列op_queue[max_ops]，队列中封装了相关的read，write回调函数操作；
2)deadline_timer_service::struct implementation_type信息如下：
1 struct implementation_type 2 : private boost::asio::detail::noncopyable 3 { 4 time_type expiry; 5 bool might_have_pending_waits; 6 typename timer_queue<Time_Traits>::per_timer_data timer_data; 7 };
其中per_timer_data的结构体如下：
1 class per_timer_data 2 { 3 public: 4 per_timer_data() : next_(0), prev_(0) {} 5 6 private: 7 friend class timer_queue; 8 9 // The operations waiting on the timer. 10 op_queue<wait_op> op_queue_; 11 12 // The index of the timer in the heap. 13 std::size_t heap_index_; 14 15 // Pointers to adjacent timers in a linked list. 16 per_timer_data* next_; 17 per_timer_data* prev_; 18 };
通过index我们可以从io_service中区分出不同的deadline_timer;
epoll_event中的event.data.ptr保存的就是implementation中per_xx_data的指针