Re: mutex problems on Windows

[Chris Vine <chris cvine freeserve co uk>]

On Mon, 6 Jul 2009 17:13:07 +0300
Dov Grobgeld <dov grobgeld gmail com> wrote:

> I'm having a problem with GMutex under Windows that don't lock. The
> behaviour is definitely different from that under Linux.
> 
> The system is composed of to threads. A gui thread G and a worker
> thread W. The ping pong between the threads via a mutex j->M should
> work as follows. j is a job data structure that carries info between
> the worker thread and the gui thread.
> 
>    1. W locks j->M through g_mutex_lock(j->M) so that a subsequent
> lock will block.
>    2. W fills in j with various info to display.
>    3. W calls g_idle_add(GSourceFunc(cb_update_job), j) to indicate
> to G that there is info to display.
>    4. W blocks on M through a second call to g_mutex_lock(j->M)
>    5. G is called in cb_update_job() and updates the gui, also
> possibly updates j, and then does g_mutex_unlock(j->M)
>    6. W wakes up and does a g_mutex_unlock(j->M) as it no longer
> needs the lock on the mutex.
>    7. W examines the return info that G filled in into j and contiues
> or aborts its operation.
> 
> The problem on Win32 is that g_mutex_lock in 4 doesn't block and the
> thread continues, which eventually will cause the system to crash.
> 
> Is something supposed to be different under Windows, or should I file
> a bug?

This won't work.  Mutexes have ownership once locked.  An unlock
operation on a mutex must be carried out by the same thread that locked
it.

You could use condition variables to achieve what you want.  It would
also be wise to read up a little more on threading, and in particular
pthreads (which GThreads mimic).

Chris