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List:       kde-core-devel
Subject:    Re: threads
From:       Waldo Bastian <bastian () suse ! de>
Date:       1999-12-03 14:08:32
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On Fri, 03 Dec 1999, Dirk A. Mueller wrote:
> On Fre, 03 Dez 1999, Lubos Lunak wrote:
> 
> > Well, Pth is cooperative multithreading library, and has exactly defined
> > context-switch points 
> 
> that's the problem. _cooperative_ multithreading is in no way better than
> the current QTimer solution. If one thread blocks, the whole app will hang. 

Summary:
========

Its basically impossible to get pre-emptive multithreading reliable.

Cooperative multithreading is an option. The benefit is that it is much easier 
to program a worker thread than QTimer beased state machine. The disadvanatge 
is that calls like fopen() still block. 

The other option is to use processes as we do with the io_slaves. The 
disadvantage here is that it requires more memory and the IPC is somewhat 
slower. The advantage is that a dying io_slave doen't crash your application.


Discussion:
=========

In theory you can do cooperative multithreading toghether with kernel-threads. 
Whenever you are about to enter a possible-blocking system call, you use a 
kernel-thread for this. This way you can make it that you keep the semantics of 
cooperative-multithreading but you don't have the disadvantage of blocking on
system calls.

(A quick & dirty way to get this behaviour is to use kernel-threads and lock a 
mutex all the time except for when you are about to enter a system call.)

Cheers,
Waldo

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