Proactor 學習1

Proactor    An Object Behavioral Pattern for Demultiplexingand Dispatching Handlers for Asynchronous Events

Douglas C. Schmidt

Known Uses

The following are some widely documented uses of the Proctor pattern:

I/O Completion Ports in Windows NT:

The Windows NT operating system implements the Proactor pattern.

Various Asynchronous Operations such as accepting new network connections, reading and writing to files and
sockets, and transmission of files across a network connection are supported by Windows NT.

The operating system is the Asynchronous Operation Processor.

Results of the operations are queued up at the I/O completion port

(which plays the role of the Completion Dispatcher).

The UNIX AIO Family of Asynchronous I/O Operations:

On some real-time POSIX platforms, the Proactor pattern is implemented by the aio family of APIs 

These OS features are very similar to the ones described above for Windows NT.

One difference is that UNIX signals can be used to implement an truly asynchronous Completion Dispatcher (the Windows NT API is not truly asynchronous).

ACE Proactor: 

The Adaptive Communications Environment (ACE)  implements a Proactor component that encapsulates I/O Completion Ports on Windows NT and the  aio APIs on POSIX platforms. 

The ACE Proactor abstraction provides an OO interface to the standard C APIs supported by Windows NT.

Asynchronous Procedure Calls in Windows NT:

Some
systems (such as Windows NT) support Asynchronous Procedure Calls (APC)s.

An APC is a function that executes asynchronously in the context of a particular thread.

When an APC is queued to a thread, the system issues a software interrupt. 

The next time the thread is scheduled, it will run the APC.

 APCs made by operating system are called kernelmode APCs. APCs made by an application are called usermode APCs.

在windowsserver中要建立高性能,靈活server一定涉及到IOCP的使用。而IOCP又是Proactor Pattern的實踐。

同一時候隨着java跨平臺語言的發展。java語言在JDK7(2009年)提供了對於Asyn IO的支持，爲java語言做爲跨平臺網絡server提供了更好的支持。

java NIO中的Aysn I/O 同一時候也是一種對於Proactor Pattern的實踐。