Subj : Re: pthread_cond_broadcast [a little long]
To   : comp.programming.threads
From : David Schwartz
Date : Tue Jan 25 2005 03:49 pm


"fabrizio" <watch.the@stars.fr> wrote in message 
news:ct5e0k$rnb$1@utcnews.utc.fr...

> I am trying to synchronize a certain number of threads
> using condvars and encounter some problems.

    You have no predicate.

> I create a thread that wait for x signals and then broadcast
> a convar that should start all other threads.

    No, that's not how you use condition variables.

> Unfortunately, as the last ready thread signal the ready condvar
> the thread waiting for the ready event, immediately signal the start order 
> and the last thread has not yet reach the wait instruction.

    This is a common misunderstanding. 'pthread_cond_wait' is *not a 
conditional wait, it's an unconditional wait *for* a condition. It is vital 
that you call 'pthread_cond_wait' in a while loop (or similar), and it is 
vital that your program keep track of what it is that's being waited for.

    DS

.