Re: [OT] Win32 condition variable implementation

mark benedetto king <mbk@lowlatency.com> writes:

> wait(cond,mutex):
> acquire(cond->mutex)
> cond->num_waiters++
> release(cond->mutex)
> release(mutex)
> down(cond->sem)
> up(cond->ack)
> acquire(mutex)
>
> deliver(cond,count):
> up(cond->sem, count)
> down(cond->ack, count)
> count->num_waiters -= count
>
> signal(cond):
> acquire(cond->mutex)
> deliver(cond, min(1, cond->num_waiters))
> release(cond->mutex)
>
> broadcast(cond):
> acquire(cond->mutex)
> deliver(cond, cond->num_waiters);
> release(cond->mutex)

 thread 1 waits
 thread 2 waits
 thread 3 broadcasts
 thread 1 wakes up and runs
 thread 1 acquires mutex and calls wait
 thread 1 blocks waiting for cond->mutex held by thread 3
 thread 2 tries to wake up but blocks waiting for mutex held by thread 1
 deadlock

-- 
Philip Martin
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