Proactor和Reactor模式_继续并发系统设计的扫盲.doc

Proactor和Reactor模式_继续并发系统设计的扫盲 6.6.2008 Kevin Lynx 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。 摘抄一些关键的东西： 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. 关于两个模式的大致模型，从以下文字基本可以明白： 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. Heres a read in Reactor: * 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 . By comparison, here is a read operation in Proactor (true async): * 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. 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hand