69a
Subj : Re: CondVar on Windows : what to do when a consumer thread is killed
To   : comp.programming.threads
From : adebaene
Date : Fri Jul 01 2005 05:49 am



Joe Seigh a =E9crit :
> adebaene@club-internet.fr wrote:
>
> >
> > What does Posix says on behaviour of a condvar whenever a waiting
> > thread is killed?
> >
> That's there's one less thread waiting.  You should stop killing off
> your threads that way.   Anyway, it's something you deliberately did
> so you should be able to handle it.
>
> How did you kill the thread?
I didn't killed the thread, the system did :-)

The context is the following : a static singleton object starts a
worker thread in it's constructor. Communication between the main
thread and this worker thread is by the means of a blocking queue,
which is implemented using a condvar.

During the singleton destruction, a special message is posted to this
queue to signal the worker thread to stop, and posting to the queue
implies calling pthread_cond_broadcast.
The problem is that, since the singelton is a static object, it's
destructor runs during CRT termination cleanup, *after* the system has
forcibly killed all worker threads --> deadlock  :-(

> A signal isn't guaranteed to generate
> a spurious wakeup.
What do you mean exactly? There is nothing left to wakeup since the
consumer thread has been killed...

>  If you  used pthread cancel then your cleanup
> handlers should have taken care of the problem.
I am working on Windows and do not use pthreads, but Win32 threading
API (in fact, my condvar hasn't got exactly the pthread_condvar
interface - although it has the  same semantic).

Arnaud

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