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ACE Reactor框架设计的目标是，实现一种灵活的事件处理机制，使应用无需为了满足事件处理的需要而编写平台相关的中心代码。使用Reactor框架，应用要实现其事件处理只需要做三件事情。
ONE：从 ACE_Event_Handler 派生一个或多个类，并给各个虚回调方法增加应用特有的事件处理行为。
#include <ace/Event_Handler.h>
//...
class Service : public ACE_Event_Handler
{
/// 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. <current_time> represents the current
* time that the <Event_Handler> was selected for timeout
* dispatching and <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
/// <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);
virtual int handle_qos (ACE_HANDLE = ACE_INVALID_HANDLE);
virtual int handle_group_qos (ACE_HANDLE = ACE_INVALID_HANDLE);
/// Get the I/O handle.
virtual ACE_HANDLE get_handle (void) const;
//根据应用选择性的重载
}
TWO：向 ACE_Reactor 类登记应用的事件处理对象，把每个事件处理对象与它感兴趣的事件关联起来。
先看ACE_Reactor（<ace/Reactor.h>）成员register_handler一个声明（还有其它几个传不同参数）：
/**
* Register handler for I/O events.
*
* A handler can be associated with multiple handles. A handle
* cannot be associated with multiple handlers.
*
* The handle will come from ACE_Event_Handler::get_handle().
*
* Reactor will call ACE_Event_Handler::add_reference() for a new
* handler/handle pair.
*
* If this handler/handle pair has already been registered,any new
* masks specified will be added. In this case,
* ACE_Event_Handler::add_reference() will not be called.
*
* If the registered handler is currently suspended,it will remain
* suspended. When the handler is resumed,it will have the
* existing masks plus any masks added through this call. Handlers
* do not have partial suspensions.
*/
virtual int register_handler (ACE_Event_Handler *event_handler,
ACE_Reactor_Mask mask);
ACE_Reactor_Mask声明于 <ace/Event_Handler.h> 中：
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)
};
你可在 Service 类中，把每个事件处理对象与它感兴趣的事件关联起来：
this->reactor()->register_handler(this,ACE_Event_Handler::READ_MASK);//关联virtual int handle_input (ACE_HANDLE fd = ACE_INVALID_HANDLE);回调函数。
向 ACE_Reactor 类登记应用的事件处理对象：
Service service;
service.reactor(ACE_Reactor::instance());
THREE：运行 ACE_Reactor 事件循环。 ACE_Reactor::instance()->run_reactor_event_loop(); //还有其它的几个循环函数，还没有具体研究可以看出，我们用的是一个 ACE_Reactor 单件，由 ACE_Object_Manager 管理它。 （编辑：李大同）
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