Re: [Boost-users] async_XXX() functions

From: Boris (boriss_at_[hidden])
Date: 2008-05-30 23:24:49

On Sat, 31 May 2008 02:33:53 +0900, Longyu Mei <lmei007_at_[hidden]> wrote:

> I noticed that there are couple of async_XXX methods, such as  
> async_wait, async_connect, async_write and async_fill. Just wondering  
> why we need those async_XXX methods?

I assume that you are referring to the library Boost.Asio?

> without the "async", those methods will block the execution and next  
> statements will be deferred. with the "async", those methods will return  
> immediately and the work will be deferred a little time but will still  
> be executed in the same thread.

Yes, that's the idea. :)

> I feel it confuses people. If we need next statements being executed  
> immediately, we can use another thread to do the wait, connect, write or  
> fill. It is more clear and clean. And the user/programmer has fully  
> control on this.

Depending on the operating system there might be more efficient APIs  
available as if you would need to use a thread for every blocking function  
(eg. you don't need 100 threads in a server with 100 connections if you  
use select()). I wouldn't necessarily agree either that using threads is  
always clearer and cleaner - just think about synchronizing them. As it  
might be necessary though to use a thread to make some functions support  
the asynchronous I/O model of Boost.Asio: That's completely transparent to  
the user. Even if there is a thread used in the background you don't need  
to worry about it as your code (the handlers) are executed in the same  
thread. The synchronization is done by Boost.Asio automatically - that I  
call clear and clean. :)

Boris