2. ACE_Select_Reactor_T 介绍

该类继承自类ACE_Select_Reactor_Impl，实现了对IO时间、信号量、定时器的分发处理，公共的函数需要ACE_Reactor_Token进行锁定。typedef ACE_Select_Reactor_T<ACE_Select_Reactor_Token> ACE_Select_Reactor定义了常用的ACE_Select_Reactor类，可以在程序中直接使用。

2.1. 类继承图

2.2. 类协作图

ACE_Select_Reactor 核心交互图，表明了 ACE_Select_Reactor 针对 Socket/IO, 定时器，通知和信号量的整体数据结构。

2.3. 类主要成员变量

ACE_Select_Reactor_Impl继承自 ACE_Reactor_Impl，在类ACE_Select_Reactor_Impl中定义了常用的成员变量：

ace/Select_Reactor_Base.h

  /// 提供<ACE_HANDLE>到<ACE_Event_Handler *>的映射
  ACE_Select_Reactor_Handler_Repository handler_rep_;

  /// 跟踪使用select函数返回的已触发的handle
  ACE_Select_Reactor_Handle_Set dispatch_set_;

  /// 跟踪要被select函数跟踪的句柄
  ACE_Select_Reactor_Handle_Set wait_set_;

  /// 跟踪当前被挂起的句柄
  ACE_Select_Reactor_Handle_Set suspend_set_;

  /// 跟踪我们感兴趣但不使用select函数触发的其他类型的各种句柄，例如 handle_*() 函数的返回值大于 0
  ACE_Select_Reactor_Handle_Set ready_set_;

  /// 定义时间轮队列指针，默认为：ACE_Timer_Heap
  ACE_Timer_Queue *timer_queue_;

  /// 处理信号量而不是用全局/静态的变量
  ACE_Sig_Handler *signal_handler_;

  /// 回调对象用于唤醒睡眠中的ACE_Select_Reactor，默认为ACE_Select_Reactor_Notify
  ACE_Reactor_Notify *notify_handler_;

  /// 跟踪是否需要我们自己负责删除时间队列标志
  bool delete_timer_queue_;

  /// 跟踪是否需要我们自己删除信号句柄
  bool delete_signal_handler_;

  /// 跟踪是否需要我们自己删除通知句柄
  bool delete_notify_handler_;

  /// 是否进行初始化的标记
  bool initialized_;

  /// 是否自动重启<handle_events>的事件循环，如果select被信号量中断
  bool restart_;

  /// 表明ACE_Select_Reactor主线程在<notify>回调等待列表中的位置。如果等于-1表明在list的尾部，
  /// 0表明在队列首部，如果大于1表明队列等待队列需要处理的数目
  int requeue_position_;

  /// 创建该类的的原始线程
  ACE_thread_t owner_;

  /// 如果为true表明state已经在ACE_Event_Handler派发过程中发生了变化。这用于确定我们是否
  /// 需要在<Select_Reactor>的<wait_for_multiple_events>循环中做做另外一次迭代
  /// ACE_Select_Reactor_Impl::clear_dispatch_mask (ACE_HANDLE handle,ACE_Reactor_Mask mask)中修改了
  /// dispatch_set_中的handle的mask，则会将该状态设置成true。
  bool state_changed_;

  /// 如果为false，则reactor在事件分发过程中将不屏蔽信号量。这对于不注册任何信号量句柄的程序非常有用，
  /// 如果修改这个mask的值，可以减少内核层次锁的开销
  bool mask_signals_;

注解

其中ACE_Select_Reactor_Handler_Repository handler_rep_的数据结构定义，可参见 bind 函数 。

2.4. 事件处理函数调用图

注解

calculate_timeout 函数的调用为类实现中 timer_queue_ 时间队列中最早到期时间，以便设置后续 select 调用函数的超时时间，从而实现了时间队列与IO句柄触发的整合。

2.5. 事件处理主流程

ace/Reactor.cpp

int
ACE_Reactor::run_reactor_event_loop (ACE_Time_Value &tv,
                                     REACTOR_EVENT_HOOK eh)
{
  ACE_TRACE ("ACE_Reactor::run_reactor_event_loop");

  if (this->reactor_event_loop_done ())
    return 0;

  while (1)
    {
      int result = this->implementation_->handle_events (tv);

      if (eh != 0 && (*eh) (this))
        continue;
      else if (result == -1)
        {
          if (this->implementation_->deactivated ())
            result = 0;
          return result;
        }
      else if (result == 0)
        {
          // The <handle_events> method timed out without dispatching
          // anything.  Because of rounding and conversion errors and
          // such, it could be that the wait loop (WFMO, select, etc.)
          // timed out, but the timer queue said it wasn't quite ready
          // to expire a timer. In this case, the ACE_Time_Value we
          // passed into handle_events won't have quite been reduced
          // to 0, and we need to go around again. If we are all the
          // way to 0, just return, as the entire time the caller
          // wanted to wait has been used up.
          if (tv.usec () > 0)
            continue;
          return 0;
        }
      // Else there were some events dispatched; go around again
    }

  ACE_NOTREACHED (return 0;)
}

行12行，Reactor调用了其实现者的 handle_events(ACE_Time_Value *max_wait_time) 函数，实现类的handle_event函数承担了主要工作的分发和处理。

2.5.1. handle_events 函数流程

ace/Select_Reactor_T.cpp handle_events 函数

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::handle_events
  (ACE_Time_Value *max_wait_time)
{
  ACE_TRACE ("ACE_Select_Reactor_T::handle_events");

  // Stash the current time -- the destructor of this object will
  // automatically compute how much time elapsed since this method was
  // called.
  ACE_Countdown_Time countdown (max_wait_time);

#if defined (ACE_MT_SAFE) && (ACE_MT_SAFE != 0)

  ACE_GUARD_RETURN (ACE_SELECT_REACTOR_TOKEN, ace_mon, this->token_, -1);

  if (ACE_OS::thr_equal (ACE_Thread::self (), this->owner_) == 0)
    {
      errno = EACCES;
      return -1;
    }
  if (this->deactivated_)
    {
      errno = ESHUTDOWN;
      return -1;
    }

  // Update the countdown to reflect time waiting for the mutex.
  countdown.update ();
#else
  if (this->deactivated_)
    {
      errno = ESHUTDOWN;
      return -1;
    }
#endif /* ACE_MT_SAFE */

  return this->handle_events_i (max_wait_time);
}

2.5.2. handle_events_i 函数流程

ace/Select_Reactor_T.cpp handle_events_i 函数

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::handle_events_i
  (ACE_Time_Value *max_wait_time)
{
  int result = -1;

  ACE_SEH_TRY
    {
      // We use the data member dispatch_set_ as the current dispatch
      // set.

      // We need to start from a clean dispatch_set
      this->dispatch_set_.rd_mask_.reset ();
      this->dispatch_set_.wr_mask_.reset ();
      this->dispatch_set_.ex_mask_.reset ();

      int number_of_active_handles =
        this->wait_for_multiple_events (this->dispatch_set_,
                                        max_wait_time);

      result =
        this->dispatch (number_of_active_handles,
                        this->dispatch_set_);
    }
  ACE_SEH_EXCEPT (this->release_token ())
    {
      // As it stands now, we catch and then rethrow all Win32
      // structured exceptions so that we can make sure to release the
      // <token_> lock correctly.
    }

  return result;
}

行18, this->wait_for_multiple_events (this->dispatch_set_,max_wait_time) 实现了对于可分发句柄集的获取。

行21，this->dispatch (number_of_active_handles,this->dispatch_set_) 实现了对于分发句柄集的处理。

2.5.2.1. wait_for_multiple_events 函数

ace/Select_Reactor_T.cpp wait_for_multiple_events 函数

// Must be called with lock held.

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::wait_for_multiple_events
  (ACE_Select_Reactor_Handle_Set &dispatch_set,
   ACE_Time_Value *max_wait_time)
{
  ACE_TRACE ("ACE_Select_Reactor_T::wait_for_multiple_events");
  ACE_Time_Value timer_buf (0);
  ACE_Time_Value *this_timeout = 0;

  int number_of_active_handles = this->any_ready (dispatch_set);

  // If there are any bits enabled in the <ready_set_> then we'll
  // handle those first, otherwise we'll block in <select>.

  if (number_of_active_handles == 0)
    {
      do
        {
          if (this->timer_queue_ == 0)
            return 0;

          this_timeout =
            this->timer_queue_->calculate_timeout (max_wait_time,
                                                   &timer_buf);
#ifdef ACE_WIN32
          // This arg is ignored on Windows and causes pointer
          // truncation warnings on 64-bit compiles.
          int const width = 0;
#else
          int const width = this->handler_rep_.max_handlep1 ();
#endif  /* ACE_WIN32 */

          dispatch_set.rd_mask_ = this->wait_set_.rd_mask_;
          dispatch_set.wr_mask_ = this->wait_set_.wr_mask_;
          dispatch_set.ex_mask_ = this->wait_set_.ex_mask_;
          number_of_active_handles = ACE_OS::select (width,
                                                     dispatch_set.rd_mask_,
                                                     dispatch_set.wr_mask_,
                                                     dispatch_set.ex_mask_,
                                                     this_timeout);
        }
      while (number_of_active_handles == -1 && this->handle_error () > 0);

      if (number_of_active_handles > 0)
        {
#if !defined (ACE_WIN32)
          // Resynchronize the fd_sets so their "max" is set properly.
          dispatch_set.rd_mask_.sync (this->handler_rep_.max_handlep1 ());
          dispatch_set.wr_mask_.sync (this->handler_rep_.max_handlep1 ());
          dispatch_set.ex_mask_.sync (this->handler_rep_.max_handlep1 ());
#endif /* ACE_WIN32 */
        }
      else if (number_of_active_handles == -1)
        {
          // Normally, select() will reset the bits in dispatch_set
          // so that only those filed descriptors that are ready will
          // have bits set.  However, when an error occurs, the bit
          // set remains as it was when the select call was first made.
          // Thus, we now have a dispatch_set that has every file
          // descriptor that was originally waited for, which is not
          // correct.  We must clear all the bit sets because we
          // have no idea if any of the file descriptors is ready.
          //
          // NOTE: We dont have a test case to reproduce this
          // problem. But pleae dont ignore this and remove it off.
          dispatch_set.rd_mask_.reset ();
          dispatch_set.wr_mask_.reset ();
          dispatch_set.ex_mask_.reset ();
        }
    }

  // Return the number of events to dispatch.
  return number_of_active_handles;
}

行12,，this->any_ready(dispatch_set) 实现了获取不需要select函数触发的其他类型满足触发条件的句柄

行25-26，this->timer_queue_->calculate_timeout(max_wait_time,&timer_buf) 实现了对定时器队列的超时的计算

行38-42，ACE_OS::select(width,dispatch_set.rd_mask_,dispatch_set.wr_mask_,dispatch_set.ex_mask_,this_timeout) 实现了对使用select函数返回的已触发的handle的跟踪

2.5.2.2. dispatch 函数

ace/Select_Reactor_T.cpp dispatch 函数

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::dispatch
  (int active_handle_count,
   ACE_Select_Reactor_Handle_Set &dispatch_set)
{
  ACE_TRACE ("ACE_Select_Reactor_T::dispatch");

  int io_handlers_dispatched = 0;
  int other_handlers_dispatched = 0;
  int signal_occurred = 0;
  // The following do/while loop keeps dispatching as long as there
  // are still active handles.  Note that the only way we should ever
  // iterate more than once through this loop is if signals occur
  // while we're dispatching other handlers.

  do
    {
      // We expect that the loop will decrease the number of active
      // handles in each iteration.  If it does not, then something is
      // inconsistent in the state of the Reactor and we should avoid
      // the loop.  Please read the comments on bug 2540 for more
      // details.
      int initial_handle_count = active_handle_count;

      // Note that we keep track of changes to our state.  If any of
      // the dispatch_*() methods below return -1 it means that the
      // <wait_set_> state has changed as the result of an
      // <ACE_Event_Handler> being dispatched.  This means that we
      // need to bail out and rerun the select() loop since our
      // existing notion of handles in <dispatch_set> may no longer be
      // correct.
      //
      // In the beginning, our state starts out unchanged.  After
      // every iteration (i.e., due to signals), our state starts out
      // unchanged again.

      this->state_changed_ = false;

      // Perform the Template Method for dispatching all the handlers.

      // First check for interrupts.
      if (active_handle_count == -1)
        {
          // Bail out -- we got here since <select> was interrupted.
          if (ACE_Sig_Handler::sig_pending () != 0)
            {
              ACE_Sig_Handler::sig_pending (0);

              // If any HANDLES in the <ready_set_> are activated as a
              // result of signals they should be dispatched since
              // they may be time critical...
              active_handle_count = this->any_ready (dispatch_set);

              // Record the fact that the Reactor has dispatched a
              // handle_signal() method.  We need this to return the
              // appropriate count below.
              signal_occurred = 1;
            }
          else
            return -1;
        }

      // Handle timers early since they may have higher latency
      // constraints than I/O handlers.  Ideally, the order of
      // dispatching should be a strategy...
      else if (this->dispatch_timer_handlers (other_handlers_dispatched) == -1)
        // State has changed or timer queue has failed, exit loop.
        break;

      // Check to see if there are no more I/O handles left to
      // dispatch AFTER we've handled the timers...
      else if (active_handle_count == 0)
        return io_handlers_dispatched
          + other_handlers_dispatched
          + signal_occurred;

      // Next dispatch the notification handlers (if there are any to
      // dispatch).  These are required to handle multi-threads that
      // are trying to update the <Reactor>.

      else if (this->dispatch_notification_handlers
               (dispatch_set,
                active_handle_count,
                other_handlers_dispatched) == -1)
        // State has changed or a serious failure has occured, so exit
        // loop.
        break;

      // Finally, dispatch the I/O handlers.
      else if (this->dispatch_io_handlers
               (dispatch_set,
                active_handle_count,
                io_handlers_dispatched) == -1)
        // State has changed, so exit loop.
        break;

      // if state changed, we need to re-eval active_handle_count,
      // so we will not end with an endless loop
      if (initial_handle_count == active_handle_count
          || this->state_changed_)
      {
        active_handle_count = this->any_ready (dispatch_set);
      }
    }
  while (active_handle_count > 0);

  return io_handlers_dispatched + other_handlers_dispatched + signal_occurred;
}

处理顺序：

dispatch_timer_handlers 处理分发定时器，定时器的处理优于Socket/IO的处理。展开流程见： 定时器与Select_Reactor的分发集成。
dispatch_notification_handlers 处理分发通知类消息。展开流程见： 通知与Select_Reactor 的分发集成。
dispatch_io_handlers 处理分发 io handlers。展开流程见： IO句柄与Select_Reactor的分发集成。

ACE_Select_Reactor_T 介绍 (2)

2.5.2.1. wait_for_multiple_events 函数

2.5.2.2. dispatch 函数