Proactor和Reactor都是并发编程的设计模式。不同之处在于,Proactor是异步,Reactor是同步阻塞。
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: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。
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. Here's 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.
"