http://www.artima.com/articles/io_design_patterns.html

转载自：http://www.cppblog.com/kevinlynx/archive/2008/06/06/52356.html

Proactor和Reactor模式_继续并发系统设计的扫盲

6.6.2008@H_403_11@

Kevin Lynx@H_403_11@

Proactor和Reactor都是并发编程中的设计模式。在我看来，他们都是用于派发/分离IO操作事件的。这里所谓的
IO事件也就是诸如read/write的IO操作。"派发/分离"就是将单独的IO事件通知到上层模块。两个模式不同的地方
在于，Proactor用于异步IO，而Reactor用于同步IO。@H_403_11@

摘抄一些关键的东西：@H_403_11@

"
Two patterns that involve event demultiplexors are called Reactor and Proactor [1]. The Reactor patterns
involve synchronous I/O,whereas the Proactor pattern involves asynchronous I/O.
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关于两个模式的大致模型，从以下文字基本可以明白：@H_403_11@

"
An example will help you understand the difference between Reactor and Proactor. We will focus on the read
operation here,as the write implementation is similar. Here's a read in Reactor:@H_403_11@

* An event handler declares interest in I/O events that indicate readiness for read on a particular socket ;
* The event demultiplexor waits for events ;
* An event comes in and wakes-up the demultiplexor,and the demultiplexor calls the appropriate handler;
* The event handler performs the actual read operation,handles the data read,declares renewed interest in
I/O events,and returns control to the dispatcher .@H_403_11@

By comparison,here is a read operation in Proactor (true async):@H_403_11@

* A handler initiates an asynchronous read operation (note: the OS must support asynchronous I/O). In this
case,the handler does not care about I/O readiness events,but is instead registers interest in receiving
completion events;
* The event demultiplexor waits until the operation is completed ;
* While the event demultiplexor waits,the OS executes the read operation in a parallel kernel thread,puts
data into a user-defined buffer,and notifies the event demultiplexor that the read is complete ;
* The event demultiplexor calls the appropriate handler;
* The event handler handles the data from user defined buffer,starts a new asynchronous operation,and returns
control to the event demultiplexor.@H_403_11@

"@H_403_11@

可以看出，两个模式的相同点，都是对某个IO事件的事件通知(即告诉某个模块，这个IO操作可以进行或已经完成)。在结构
上，两者也有相同点：demultiplexor负责提交IO操作(异步)、查询设备是否可操作(同步)，然后当条件满足时，就回调handler。
不同点在于，异步情况下(Proactor)，当回调handler时，表示IO操作已经完成；同步情况下(Reactor)，回调handler时，表示
IO设备可以进行某个操作(can read or can write)，handler这个时候开始提交操作。@H_403_11@

用select模型写个简单的reactor，大致为：@H_403_11@

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