Jonathan Wakely wrote:
On Tue, Mar 29, 2005 at 04:36:42PM +0300, Boris wrote:
Robert Ramey wrote:
Windows has the concept of "Overlapped I/O" which permits dispatch of an i/o request that invokes a call back when done.
Posix has aio which functions (I believe) in a similar way.
So one has the concept of asyncronous i/o without any explicit reference to threads at least at the application level.
I am not sure if I understand correctly. Just as Don I think we can't get around threads when we have callbacks. I don't know about Windows but the callback in aio (Posix) is done by creating a new thread.
How the kernel chooses to implement the aio system calls is an implementation detail - it certainly doesn't require use of Boost.Thread types! I think what Robert was saying is that an application can use POSIX aio without ever having to use or know about POSIX threads.
But the application programmer still must understand that the callback function is executed as a thread as otherwise he could mess up everything if he believes his application is single-threaded.
You and Don seem to be requiring that the application explicitly create and manage threads. Several people have suggested they'd like to use some form of AIO without having to use threads.
I think Don and me were talking about callbacks where we think they can't be implemented without threads. However I don't mind if the library creates and manages threads. If we don't use threads for callbacks the one and only thread in the application has to wait or poll - this is possible eg. in .NET which is very flexible about asynchronous operations (see http://blogs.msdn.com/cbrumme/archive/2003/05/06/51385.aspx). However if you want to wait or poll you don't use an asynchronous model at all but just do non-blocking calls or block in a select() (multiplexing model). Maybe the confusion comes from that I have a network library in mind and others think about asynchronicity in general? Boris