很容易知道 ACE_Event_Handler 实现是采用的观察着模式 ，采用登记入 反应器， 是反应器的一个组件。就好像java

的窗体事件监听处理机制。

====================================================================

#include "ACE/Reactor.h"

#include "ACE/Event_Handler.h"

#define SIGWINCH 28

#define SIGINT 2 //按下control + c

class MyEventHandler: public ACE_Event_Handler

{

int handle_signal(int signum,siginfo_t*,ucontext_t*) //处理信号

{

switch(signum)

{

case SIGWINCH: ACE_DEBUG((LM_DEBUG,"You pressed SIGWINCH \n"));

break;

case SIGINT: ACE_DEBUG((LM_DEBUG,"You pressed SIGINT \n"));

break;

}

return 0;

}

};

int main(int argc,char *argv[])

{

MyEventHandler *eh =new MyEventHandler;

ACE_Reactor::instance()->register_handler(SIGWINCH,eh); //注册信号1

ACE_Reactor::instance()->register_handler(SIGINT,eh); //注册信号2

while(1)

ACE_Reactor::instance()->handle_events();

}

==========================================================

ACE_Event_Handler中在子类中重载，所处理事件的类型:

的处理方法

handle_signal() 信号。当任何在反应器上登记的信号发生时，反应器自动回调该

方法。

handle_input() 来自I/O设备的输入。当I/O句柄（比如UNIX中的文件描述符）

上的输入可用时，反应器自动回调该方法。

handle_exception() 异常事件。当已在反应器上登记的异常事件发生时（例如，如果

收到SIGURG（紧急信号）），反应器自动回调该方法。

handle_timeout() 定时器。当任何已登记的定时器超时的时候，反应器自动回调该

方法。

handle_output() I/O设备输出。当I/O设备的输出队列有可用空间时，反应器自动

回调该方法。

源代码：

/* -*- C++ -*- */

//==========================================================================
/**
 *  @file    Event_Handler.h
 *
 *  $Id: Event_Handler.h 92345 2010-10-24 12:39:33Z johnnyw $
 *
 *  @author Douglas C. Schmidt <schmidt@cs.wustl.edu>
 */
//==========================================================================

#ifndef ACE_EVENT_HANDLER_H
#define ACE_EVENT_HANDLER_H
#include /**/ "ace/pre.h"

#include /**/ "ace/ACE_export.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include "ace/os_include/os_signal.h"
#include "ace/Atomic_Op.h"
#include "ace/Synch_Traits.h"

ACE_BEGIN_VERSIONED_NAMESPACE_DECL

// Forward declaration.
class ACE_Message_Block;
class ACE_Reactor;
class ACE_Reactor_Timer_Interface;
class ACE_Thread_Manager;
class ACE_Process;

typedef unsigned long ACE_Reactor_Mask;

/**
 * @class ACE_Event_Handler
 *
 * @brief
 * Provides an abstract interface for handling varIoUs types of
 * I/O,timer,and signal events.
 *
 * Subclasses read/write input/output on an I/O descriptor,* handle an exception raised on an I/O descriptor,handle a
 * timer's expiration,or handle a signal.
 */
class ACE_Export ACE_Event_Handler
{
public:
  enum
  {
    LO_PRIORITY = 0,HI_PRIORITY = 10,NULL_MASK = 0,#if defined (ACE_USE_POLL)
    READ_MASK = POLLIN,WRITE_MASK = POLLOUT,EXCEPT_MASK = POLLPRI,#else /* USE SELECT */
    READ_MASK = (1 << 0),WRITE_MASK = (1 << 1),EXCEPT_MASK = (1 << 2),#endif /* ACE_USE_POLL */
    ACCEPT_MASK = (1 << 3),CONNECT_MASK = (1 << 4),TIMER_MASK = (1 << 5),QOS_MASK = (1 << 6),GROUP_QOS_MASK = (1 << 7),SIGNAL_MASK = (1 << 8),ALL_EVENTS_MASK = READ_MASK |
                      WRITE_MASK |
                      EXCEPT_MASK |
                      ACCEPT_MASK |
                      CONNECT_MASK |
                      TIMER_MASK |
                      QOS_MASK |
                      GROUP_QOS_MASK |
                      SIGNAL_MASK,RWE_MASK = READ_MASK |
               WRITE_MASK |
               EXCEPT_MASK,DONT_CALL = (1 << 9)
  };

  /// Destructor is virtual to enable proper cleanup.
  virtual ~ACE_Event_Handler (void);

  /// Get the I/O handle.
  virtual ACE_HANDLE get_handle (void) const;

  /// Set the I/O handle.
  virtual void set_handle (ACE_HANDLE);

  // = Get/set priority

  /// Get the priority of the Event_Handler.
  /// @note Priorities run from MIN_PRIORITY (which is the "lowest priority")
  /// to MAX_PRIORITY (which is the "highest priority").
  virtual int priority (void) const;

  /// Set the priority of the Event_Handler.
  virtual void priority (int priority);

  /// Called when input events occur (e.g.,connection or data).
  virtual int handle_input (ACE_HANDLE fd = ACE_INVALID_HANDLE);

  /// Called when output events are possible (e.g.,when flow control
  /// abates or non-blocking connection completes).
  virtual int handle_output (ACE_HANDLE fd = ACE_INVALID_HANDLE);

  /// Called when an exceptional events occur (e.g.,SIGURG).
  virtual int handle_exception (ACE_HANDLE fd = ACE_INVALID_HANDLE);

  /**
   * Called when timer expires.  @a current_time represents the current
   * time that the Event_Handler was selected for timeout
   * dispatching and @a act is the asynchronous completion token that
   * was passed in when <schedule_timer> was invoked.
   */
  virtual int handle_timeout (const ACE_Time_Value ¤t_time,const void *act = 0);

  /// Called when a process exits.
  virtual int handle_exit (ACE_Process *);

  /// Called when a handle_*() method returns -1 or when the
  /// remove_handler() method is called on an ACE_Reactor.  The
  /// @a close_mask indicates which event has triggered the
  /// handle_close() method callback on a particular @a handle.
  virtual int handle_close (ACE_HANDLE handle,ACE_Reactor_Mask close_mask);

  /// Called when object is signaled by OS (either via UNIX signals or
  /// when a Win32 object becomes signaled).
  virtual int handle_signal (int signum,siginfo_t * = 0,ucontext_t * = 0);

  enum
    {
      /// The handler is not resumed at all. Could lead to deadlock..
      ACE_EVENT_HANDLER_NOT_RESUMED = -1,/// The reactor takes responsibility of resuming the handler and
      /// is the default
      ACE_REACTOR_RESUMES_HANDLER = 0,/// The application takes responsibility of resuming the handler
      ACE_APPLICATION_RESUMES_HANDLER
    };

  /**
   * Called to figure out whether the handler needs to resumed by the
   * reactor or the application can take care of it. The default
   * value of 0 would be returned which would allow the reactor to
   * take care of resumption of the handler. The application can
   * return a value more than zero and decide to resume the handler
   * themselves.
   *
   * @note This method has an affect only when used with the
   * ACE_Dev_Poll_Reactor (and then,only on Linux) or the ACE_TP_Reactor.
   */
  virtual int resume_handler (void);

  virtual int handle_qos (ACE_HANDLE = ACE_INVALID_HANDLE);
  virtual int handle_group_qos (ACE_HANDLE = ACE_INVALID_HANDLE);

  // = Accessors to set/get the varIoUs event demultiplexors.
  /// Set the event demultiplexors.
  virtual void reactor (ACE_Reactor *reactor);

  /// Get the event demultiplexors.
  virtual ACE_Reactor *reactor (void) const;

  /// Get only the reactor's timer related interface.
  virtual ACE_Reactor_Timer_Interface *reactor_timer_interface (void) const;

  /**
   * Used to read from non-socket ACE_HANDLEs in our own thread to
   * work around Win32 limitations that don't allow us to <select> on
   * non-sockets (such as ACE_STDIN).  This is commonly used in
   * situations where the Reactor is used to demultiplex read events
   * on ACE_STDIN on UNIX.  Note that @a event_handler must be a
   * subclass of ACE_Event_Handler.  If the get_handle() method of
   * this event handler returns ACE_INVALID_HANDLE we default to
   * reading from ACE_STDIN.
   */
  static ACE_THR_FUNC_RETURN read_adapter (void *event_handler);

  /**
   * Abstracts away from the differences between Win32 and ACE with
   * respect to reading from ACE_STDIN,which is non-<select>'able on
   * Win32.
   */
  static int register_stdin_handler (ACE_Event_Handler *eh,ACE_Reactor *reactor,ACE_Thread_Manager *thr_mgr,int flags = THR_DETACHED);

  /// Performs the inverse of the register_stdin_handler() method.
  static int remove_stdin_handler (ACE_Reactor *reactor,ACE_Thread_Manager *thr_mgr);

  /// Reference count type.
  typedef long Reference_Count;

  /// Increment reference count on the handler.
  /**
   * This method is called when the handler is registered with the
   * Reactor and when the Reactor makes an upcall on the handler.
   * Reference count is 1 when the handler is created.
   *
   * @return Current reference count.
   */
  virtual Reference_Count add_reference (void);

  /// Decrement reference count on the handler.
  /**
   * This method is called when the handler is removed from the
   * Reactor and when an upcall made on the handler by the Reactor
   * completes.  Handler is deleted when the reference count reaches
   * 0.
   *
   * @return Current reference count.
   */
  virtual Reference_Count remove_reference (void);

  /**
   * @class Policy
   *
   * @brief Base class for all handler policies.
   */
  class ACE_Export Policy
  {

  public:

    /// Virtual destructor.
    virtual ~Policy (void);
  };

  /**
   * @class Reference_Counting_Policy
   *
   * @brief
   * This policy dictates the reference counting requirements
   * for the handler.
   *
   * This policy allows applications to configure whether it wants the
   * Reactor to call add_reference() and remove_reference() during
   * registrations,removals,and upcalls.
   *
   * <B>Default:</B> DISABLED.
   */
  class ACE_Export Reference_Counting_Policy : public Policy
  {
    /// This policy can only be created by the handler.
    friend class ACE_Event_Handler;

  public:

    enum Value
      {
        /// Perform reference counting.
        ENABLED,/// Don't perform reference counting.
        DISABLED
      };

    /// Current Reference_Counting_Policy.
    Value value (void) const;

    /// Update Reference_Counting_Policy.
    void value (Value value);

  private:

    /// Private constructor.
    Reference_Counting_Policy (Value value);

    /// The value of the policy.
    Value value_;
   };

  /// Current Reference_Counting_Policy.
  Reference_Counting_Policy &reference_counting_policy (void);

protected:
  /// Force ACE_Event_Handler to be an abstract base class.
  ACE_Event_Handler (ACE_Reactor * = 0,int priority = ACE_Event_Handler::LO_PRIORITY);

  /// Typedef for implementation of reference counting.
  typedef ACE_Atomic_Op<ACE_SYNCH_MUTEX,Reference_Count> Atomic_Reference_Count;

  /// Reference count.
  Atomic_Reference_Count reference_count_;

private:

  /// Priority of this Event_Handler.
  int priority_;

  /// Pointer to the varIoUs event demultiplexors.
  ACE_Reactor *reactor_;

  /// Reference counting requirements.
  Reference_Counting_Policy reference_counting_policy_;
};

/**
 * @class ACE_Event_Handler_var
 *
 * @brief Auto pointer like class for Event Handlers.
 *
 * Used to manage lifecycle of handlers. This class calls
 * ACE_Event_Handler::remove_reference() in its destructor.
 */
class ACE_Export ACE_Event_Handler_var
{

public:

  /// Default constructor.
  ACE_Event_Handler_var (void);

  /// Construct with a handler.
  ACE_Event_Handler_var (ACE_Event_Handler *p);

  /// Copy constructor.
  ACE_Event_Handler_var (const ACE_Event_Handler_var &b);

  /// Destructor.
  ~ACE_Event_Handler_var (void);

  /// Assignment to a handler.
  ACE_Event_Handler_var &operator= (ACE_Event_Handler *p);

  /// Assignment to a ACE_Event_Handler_var.
  ACE_Event_Handler_var &operator= (const ACE_Event_Handler_var &b);

  /// Overloaded "->".
  ACE_Event_Handler *operator-> () const;

  /// Access the handler.
  ACE_Event_Handler *handler (void) const;

  /// Release the handler.
  ACE_Event_Handler *release (void);

  /// Reset the handler.
  void reset (ACE_Event_Handler *p = 0);

private:

  /// Handler.
  ACE_Event_Handler *ptr_;
};

/**
 * @class ACE_Notification_Buffer
 *
 * @brief Simple wrapper for passing <ACE_Event_Handler *>s and
 * ACE_Reactor_Masks between threads.
 */
class ACE_Export ACE_Notification_Buffer
{
public:
  ACE_Notification_Buffer (void);

  ACE_Notification_Buffer (ACE_Event_Handler *eh,ACE_Reactor_Mask mask);

  /// Default destructor.
  ~ACE_Notification_Buffer (void);

  /// Pointer to the Event_Handler that will be dispatched
  /// by the main event loop.
  ACE_Event_Handler *eh_;

  /// Mask that indicates which method to call.
  ACE_Reactor_Mask mask_;
};

ACE_END_VERSIONED_NAMESPACE_DECL

#if defined (__ACE_INLINE__)
#include "ace/Event_Handler.inl"
#endif /* __ACE_INLINE__ */

#include /**/ "ace/post.h"
#endif /* ACE_EVENT_HANDLER_H */

virtual ~ACE_Event_Handler (void); /// Get the I/O handle. virtual ACE_HANDLE get_handle (void) const; /// Set the I/O handle. virtual void set_handle (ACE_HANDLE);

都是虚函数，因此当你使用ACE_Event_Handler的时候，就要在其函数中实现自己的定义~ 。