Re: [OT] Win32 condition variable implementation

On Wed, Sep 10, 2003 at 08:22:48AM -0400, mark benedetto king wrote:
>
> wait(cond,mutex):
> acquire(cond->mutex)
> cond->num_waiters++
> release(cond->mutex)
> release(mutex)
> down(cond->sem)
> up(cond->ack)
> acquire(cond->mutex)
> cond->num_waiters--
> release(cond->mutex)
> acquire(mutex)
>
> signal(cond):
> acquire(cond->mutex)
> up(cond->sem,min(1, cond->num_waiters))
> down(cond->ack,min(1, cond->num_waiters))
> release(cond->mutex)
>
> broadcast(cond):
> acquire(cond->mutex)
> up(cond->sem,cond->num_waiters)
> down(cond->ack,cond->num_waiters);
> release(cond->mutex)
>

I spoke too soon; this implementation has a problem with

Thread1 Thread2
wait()
                 signal()
                 signal()

There is an interleaving that causes the second signal() to hang, waiting
for a waiter that can never come, since Thread2 holds cond->mutex.
I give up for today. :-)

--ben

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Received on Wed Sep 10 14:30:26 2003