ACE - Reactor模式源码剖析及具体实现（大量源码慎入）

原文出自http://www.cnblogs.com/binchen-china，禁止转载。

在之前的文章中提到过Reactor模式和Preactor模式，现在利用ACE的Reactor来实现一个基于Reactor框架的服务器。

首先回顾下Reactor模式和Preactor模式。

Reactor模式：

Reactor模式实现非常简单，使用同步IO模型，即业务线程处理数据需要主动等待或询问，主要特点是利用epoll监听listen描述符是否有响应，及时将客户连接信息放于一个队列，epoll和队列都是在主进程/线程中，由子进程/线程来接管描述符传输的数据，对描述符进行下一步操作，包括connect和数据读写。主程读写就绪事件。整个过程都需要先获取描述符状态，在状态允许下再执行任务。

大致流程图如下：

Preactor模式：

Preactor模式完全将IO处理和业务分离，使用异步IO模型，即内核完成数据处理后主动通知给应用处理，主进程/线程不仅要完成listen任务，还需要完成内核数据缓冲区的映射，直接将数据buff传递给业务线程，业务线程只需要处理业务逻辑即可。整个过程直接推送任务，描述符状态是否允许执行任务由内核去调度处理。

大致流程如下：

 

ACE的Reactor模式

所有服务器都可以归纳为以下三层：

• I/O：处理底层IO事件
• Dispatch：事件消息派发
• Service：业务处理

 

ACE的Reactor处于I/O和Dispatch层。提供了I/O监控和消息Dispatch。其中I/O需要用户以handle的形式提供到ACE_Reactor内。

Dispatch需要以ACE_Event_Handler为载体，也就是说要实现一个完整的Reactor只依赖ACE_Reactor类是无法完成的。

 

上篇博文利用ACE的Socket可以看出一个ACE_SOCK_Acceptor和ACE_SOCK_Stream就可以完成服务器代码。现在要做的是，

1.引入Reactor，把Acceptor和Stream两个I/O分别放在两个继承于ACE_Event_Handler的类中注册给ACE_Reactor。

2.主函数注册包含ACE_SOCK_Acceptor的类到ACE_Reactor中，当ACE_SOCK_Acceptor收到数据即有客户端连接后再给对应的客户端创建一个ACE_SOCK_Stream通道并注册到ACE_Reactor中。

 

使用ACE_Reactor实现的Server代码：

#include <ace/INET_Addr.h>
#include <ace/SOCK_Acceptor.h>
#include <ace/SOCK_Stream.h>
#include <ace/Reactor.h> 
#include <ace/Log_Msg.h>
#include <list>

#define MAX_BUFF_SIZE     1024
#define LISTEN_PORT     5010
#define SERVER_IP        ACE_LOCALHOST

class ServerStream : public ACE_Event_Handler
{
public:
    ServerStream();
    ~ServerStream();
    ACE_SOCK_Stream& GetStream(){return Svr_stream;}    //给accept提供接口绑定数据通道
    virtual int handle_input(ACE_HANDLE fd);    //I/O触发事件后调用
    void close();
    virtual ACE_HANDLE get_handle(void) const {return Svr_stream.get_handle();}    //不重载需要手动将handle传入ACE_Reactor
private:
    ACE_INET_Addr Cli_addr;
    ACE_SOCK_Stream Svr_stream;
};

ServerStream::ServerStream()
{

}

ServerStream::~ServerStream()
{
    close();
}

int ServerStream::handle_input(ACE_HANDLE fd)
{
    char strBuffer[MAX_BUFF_SIZE];
    int byte = Svr_stream.recv(strBuffer,MAX_BUFF_SIZE); //可读数据
    if (-1 == byte)
    {
        ACE_DEBUG((LM_INFO, ACE_TEXT("receive data failed\n")));
    }
    else if(0 == byte)
    {
        close();
        ACE_DEBUG((LM_INFO, ACE_TEXT("client closed!\n")));
    }
    else
    {
        ACE_DEBUG((LM_INFO, ACE_TEXT("receive from client: %s\n"),strBuffer));
    }
}

void ServerStream::close()
{
    Svr_stream.close();
    ACE_Reactor::instance()->remove_handler(this,ACE_Event_Handler::READ_MASK | ACE_Event_Handler::DONT_CALL);
    //delete this;
}

class ServerAcceptor : public ACE_Event_Handler
{
public:
    ServerAcceptor(int port,char* ip);
    ~ServerAcceptor();
    bool open();
    virtual int handle_input(ACE_HANDLE fd);  //有client连接
    void close();
    virtual ACE_HANDLE get_handle(void) const {return Svr_aceept.get_handle();}
private:
    ACE_INET_Addr Svr_addr;
    ACE_SOCK_Acceptor Svr_aceept;
    std::list<ServerStream*> m_streamPool;  //stream pool
};

ServerAcceptor::ServerAcceptor(int port,char* ip):Svr_addr(port,ip)
{
    if (!open())    //open listen port
    {
        ACE_DEBUG((LM_INFO, ACE_TEXT("open failed!\n")));
    }
    else
    {
        ACE_DEBUG((LM_INFO, ACE_TEXT("open success!\n")));
    }
}

ServerAcceptor::~ServerAcceptor()
{
    close();
    std::list<ServerStream*>::iterator it;
    for (it = m_streamPool.begin();it != m_streamPool.end();++it)
    {
        if (NULL != (*it))
        {
            (*it)->close();
            delete (*it);
        }
    }
}

bool ServerAcceptor::open()
{
    if (-1 == Svr_aceept.open(Svr_addr,1))
    {
        ACE_DEBUG((LM_ERROR,ACE_TEXT("failed to accept\n")));
        Svr_aceept.close();
        return false;
    }
    return true;
}

int ServerAcceptor::handle_input(ACE_HANDLE fd )  
{
    ServerStream *stream = new ServerStream();    //产生新通道
    if (NULL != stream)
    {
        m_streamPool.push_back(stream);
    }
    if (Svr_aceept.accept(stream->GetStream()) == -1)  //绑定通道
    {  
        printf("accept client fail\n");  
        return -1;  
    }
    ACE_Reactor::instance()->register_handler(stream,ACE_Event_Handler::READ_MASK);  //通道注册到ACE_Reactor
    ACE_DEBUG((LM_ERROR,ACE_TEXT("User connect success!\n")));
}  
    
void ServerAcceptor::close()
{
    ACE_Reactor::instance()->remove_handler(this,ACE_Event_Handler::ACCEPT_MASK);
    Svr_aceept.close();
}

int ACE_TMAIN()
{
    ServerAcceptor server(LISTEN_PORT,(char *)SERVER_IP);
    ACE_Reactor::instance()->register_handler(&server,ACE_Event_Handler::ACCEPT_MASK);    //listen port注册到ACE_Reactor
    ACE_Reactor::instance()->run_reactor_event_loop();  //进入消息循环，有I/O事件回调handle_input
    return 0;
}

测试结果：

终端1：

终端2：

终端3：

ACE_Reactor内部已经帮我们实现了IO复用。

 

有了Reactor的demo后，下面一步步查看ACE_Reactor内部是如何运作的：

ACE_Reactor注册EVENT，重载了一个register_handler：

int
ACE_Reactor::register_handler (ACE_Event_Handler *event_handler,
                               ACE_Reactor_Mask mask)
{
  // Remember the old reactor.
  ACE_Reactor *old_reactor = event_handler->reactor ();

  // Assign *this* <Reactor> to the <Event_Handler>.
  event_handler->reactor (this);

  int result = this->implementation ()->register_handler (event_handler, mask);
  if (result == -1)
    // Reset the old reactor in case of failures.
    event_handler->reactor (old_reactor);

  return result;
}

第11行实际是ACE_Reactor_Impl *implementation (void) const;在做实际功能。进一步查看implementation 是如何注册的。

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::register_handler
  (ACE_Event_Handler *handler,
   ACE_Reactor_Mask mask)
{
  ACE_TRACE ("ACE_Select_Reactor_T::register_handler");
  ACE_MT (ACE_GUARD_RETURN (ACE_SELECT_REACTOR_TOKEN, ace_mon, this->token_, -1));
  return this->register_handler_i (handler->get_handle (), handler, mask);
}

这里开始大量使用模板，这里重载了两个在最后调用register_handler_i，在第8行，可以看到调用了get_handle，也就是我们重载的那个函数，所以我们不需要传入ACE_Reactor，它在这一步调用了我们重新的虚函数，获得了handle，当然也可以不做重写，手动传入handle。这个handle就是我们要处理的I/O，而handler则是我们继承ACE_Event_Handler的类。

template <class ACE_SELECT_REACTOR_TOKEN> int
ACE_Select_Reactor_T<ACE_SELECT_REACTOR_TOKEN>::register_handler_i
  (ACE_HANDLE handle,
   ACE_Event_Handler *event_handler,
   ACE_Reactor_Mask mask)
{
  ACE_TRACE ("ACE_Select_Reactor_T::register_handler_i");

  // Insert the <handle, event_handle> tuple into the Handler
  // Repository.
  return this->handler_rep_.bind (handle, event_handler, mask);
}

到这里，我们看到代码handler_rep_将hande和event_handler绑定了起来，handler_rep_在Select_Reactor_Base.h内为ACE_Select_Reactor_Impl的成员变量。下面我们继续看bind实际是在做什么操作。

// Bind the <ACE_Event_Handler *> to the <ACE_HANDLE>.
int
ACE_Select_Reactor_Handler_Repository::bind (ACE_HANDLE handle,
                                             ACE_Event_Handler *event_handler,
                                             ACE_Reactor_Mask mask)
{
  ACE_TRACE ("ACE_Select_Reactor_Handler_Repository::bind");

  if (event_handler == 0)
    return -1;

  if (handle == ACE_INVALID_HANDLE)
    handle = event_handler->get_handle ();

  if (this->invalid_handle (handle))
    return -1;

  // Is this handle already in the Reactor?
  bool existing_handle = false;

#if defined (ACE_WIN32)

  map_type::ENTRY * entry = 0;

  int const result =
    this->event_handlers_.bind (handle, event_handler, entry);

  if (result == -1)
    {
      return -1;
    }
  else if (result == 1)  // Entry already exists.
    {
      // Cannot use a different handler for an existing handle.
      if (event_handler != entry->item ())
        {
          return -1;
        }
      else
        {
          // Remember that this handle is already registered in the
          // Reactor.
          existing_handle = true;
        }
    }

#else

  // Check if this handle is already registered.
  ACE_Event_Handler * const current_handler =
    this->event_handlers_[handle];

  if (current_handler)
    {
      // Cannot use a different handler for an existing handle.
      if (current_handler != event_handler)
        return -1;

      // Remember that this handle is already registered in the
      // Reactor.
      existing_handle = true;
    }

  this->event_handlers_[handle] = event_handler;

  if (this->max_handlep1_ < handle + 1)
    this->max_handlep1_ = handle + 1;

#endif /* ACE_WIN32 */

  if (this->select_reactor_.is_suspended_i (handle))
    {
      this->select_reactor_.bit_ops (handle,
                                     mask,
                                     this->select_reactor_.suspend_set_,
                                     ACE_Reactor::ADD_MASK);
    }
  else
    {
      this->select_reactor_.bit_ops (handle,
                                     mask,
                                     this->select_reactor_.wait_set_,
                                     ACE_Reactor::ADD_MASK);

      // Note the fact that we've changed the state of the <wait_set_>,
      // which is used by the dispatching loop to determine whether it can
      // keep going or if it needs to reconsult select().
      // this->select_reactor_.state_changed_ = 1;
    }

  // If new entry, call add_reference() if needed.
  if (!existing_handle)
    event_handler->add_reference ();

  return 0;
}

这里非常关键，第50行，event_handlers_实则是一个容器，handle和event_hander以index的方式绑定了起来，存储在了一个容器内，第80行还有一行关键代码，ADD_MASK形式的操作加入到了wait_set_成员内。

注册的代码到这里为止，ACE_Reactor实际上调用了几层N个文件，其实就是把handle，即I/O和handler，即继承ACE_Event_Handler的类绑定在了一个容器里。下面看ACE_Reactor是如何进行消息循环的。

int
ACE_Reactor::run_reactor_event_loop (REACTOR_EVENT_HOOK eh)
{
  ACE_TRACE ("ACE_Reactor::run_reactor_event_loop");

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

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

      if (eh != 0 && (*eh)(this))
        continue;
      else if (result == -1 && this->implementation_->deactivated ())
        return 0;
      else if (result == -1)
        return -1;
    }

  ACE_NOTREACHED (return 0;)
}

同样，将loop交给了ACE_Reactor_Impl *implementation (void) const;操作。

继续跟踪

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");

  return this->handle_events (&max_wait_time);
}

再次到了模板，调用handle_events，下面到了关键代码

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;
}

第18行wait_for_multiple_events和第22行dispatch。分别做了两件非常关键的事。

// 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;
}

第35行熟悉的变量wait_set_和第38行函数select，到这里发现，Reactor的I/O监控，就是利用select函数监控之前注册进去且ADD到wait_set_的handle，即I/O。

当有I/O事件，即返回值的number_of_active_handles不为0时，将进行dispatch。

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;
}

这里一步步按顺序进行判断分发，进入dispatch_notification_handlers，调用到Select_Reactor_Base.cpp的dispatch_notifications，到这里终于看到熟悉的函数。

// Handles pending threads (if any) that are waiting to unblock the
// Select_Reactor.

int
ACE_Select_Reactor_Notify::dispatch_notifications (int &number_of_active_handles,
                                                   ACE_Handle_Set &rd_mask)
{
  ACE_TRACE ("ACE_Select_Reactor_Notify::dispatch_notifications");

  ACE_HANDLE const read_handle =
    this->notification_pipe_.read_handle ();

  if (read_handle != ACE_INVALID_HANDLE
      && rd_mask.is_set (read_handle))
    {
      --number_of_active_handles;
      rd_mask.clr_bit (read_handle);
      return this->handle_input (read_handle);
    }
  else
    return 0;
}

第18行，调用了自己的handle_input，还不是最开始外部重载的handle_input，查看最后这个函数。

int
ACE_Select_Reactor_Notify::handle_input (ACE_HANDLE handle)
{
  ACE_TRACE ("ACE_Select_Reactor_Notify::handle_input");
  // Precondition: this->select_reactor_.token_.current_owner () ==
  // ACE_Thread::self ();

  int number_dispatched = 0;
  int result = 0;
  ACE_Notification_Buffer buffer;

  // If there is only one buffer in the pipe, this will loop and call
  // read_notify_pipe() twice.  The first time will read the buffer, and
  // the second will read the fact that the pipe is empty.
  while ((result = this->read_notify_pipe (handle, buffer)) > 0)
    {
      // Dispatch the buffer
      // NOTE: We count only if we made any dispatches ie. upcalls.
      if (this->dispatch_notify (buffer) > 0)
        ++number_dispatched;

      // Bail out if we've reached the <notify_threshold_>.  Note that
      // by default <notify_threshold_> is -1, so we'll loop until all
      // the notifications in the pipe have been dispatched.
      if (number_dispatched == this->max_notify_iterations_)
        break;
    }

  // Reassign number_dispatched to -1 if things have gone seriously
  // wrong.
  if (result < 0)
    number_dispatched = -1;

  // Enqueue ourselves into the list of waiting threads.  When we
  // reacquire the token we'll be off and running again with ownership
  // of the token.  The postcondition of this call is that
  // <select_reactor_.token_.current_owner> == <ACE_Thread::self>.
  this->select_reactor_->renew ();
  return number_dispatched;
}

第15行，取数据，第19行dispatch_notify

int
ACE_Select_Reactor_Notify::dispatch_notify (ACE_Notification_Buffer &buffer)
{
  int result = 0;

#if defined (ACE_HAS_REACTOR_NOTIFICATION_QUEUE)
  // Dispatch one message from the notify queue, and put another in
  // the pipe if one is available.  Remember, the idea is to keep
  // exactly one message in the pipe at a time.

  bool more_messages_queued = false;
  ACE_Notification_Buffer next;

  result = notification_queue_.pop_next_notification(buffer,
                                                     more_messages_queued,
                                                     next);

  if (result == 0 || result == -1)
    {
      return result;
    }

  if(more_messages_queued)
    {
      (void) ACE::send(this->notification_pipe_.write_handle(),
            (char *)&next, sizeof(ACE_Notification_Buffer));
    }
#endif /* ACE_HAS_REACTOR_NOTIFICATION_QUEUE */

  // If eh == 0 then another thread is unblocking the
  // <ACE_Select_Reactor> to update the <ACE_Select_Reactor>'s
  // internal structures.  Otherwise, we need to dispatch the
  // appropriate handle_* method on the <ACE_Event_Handler> pointer
  // we've been passed.
  if (buffer.eh_ != 0)
    {
      ACE_Event_Handler *event_handler = buffer.eh_;

      bool const requires_reference_counting =
        event_handler->reference_counting_policy ().value () ==
        ACE_Event_Handler::Reference_Counting_Policy::ENABLED;

      switch (buffer.mask_)
        {
        case ACE_Event_Handler::READ_MASK:
        case ACE_Event_Handler::ACCEPT_MASK:
          result = event_handler->handle_input (ACE_INVALID_HANDLE);
          break;
        case ACE_Event_Handler::WRITE_MASK:
          result = event_handler->handle_output (ACE_INVALID_HANDLE);
          break;
        case ACE_Event_Handler::EXCEPT_MASK:
          result = event_handler->handle_exception (ACE_INVALID_HANDLE);
          break;
        case ACE_Event_Handler::QOS_MASK:
          result = event_handler->handle_qos (ACE_INVALID_HANDLE);
          break;
        case ACE_Event_Handler::GROUP_QOS_MASK:
          result = event_handler->handle_group_qos (ACE_INVALID_HANDLE);
          break;
        default:
          // Should we bail out if we get an invalid mask?
          ACE_ERROR ((LM_ERROR,
                      ACE_TEXT ("invalid mask = %d\n"),
                      buffer.mask_));
        }

      if (result == -1)
        event_handler->handle_close (ACE_INVALID_HANDLE,
                                     ACE_Event_Handler::EXCEPT_MASK);

      if (requires_reference_counting)
        {
          event_handler->remove_reference ();
        }
    }

  return 1;
}

到这里，终于看到调用到我们最开始继承ACE_Event_Handler重写的那个回调handle_input()了。

 

至此，ACE_Reactor内部源码的执行过程全部结束，其实ACE并没有做非常特别的事，注册利用一个容器进行I/O和回调方法的绑定，I/O复用利用select，最后发生I/O事件找到对应的event函数handle_input执行。

怪不得网上有人抱怨ACE代码臃肿了，这些我们关心“简单”过程的代码就这么多的复杂用法和调用，更不用说我们还没用上的了，但是ACE提供的Reactor框架确实方便了我们使用，也提供了可靠的移植性和性能。