On Fri, 23 Mar 2001, Stelian Pop wrote:
> I want to use a semaphore for the classic producer/consumer case
> (put the consumer to wait until X items are produced, where X != 1).
>
> If X is 1, the semaphore is a simple MUTEX, ok.
>
> But if the consumer wants to wait for several items, it doesn't
> seem to work (or something is bad in my code).
>
> What is wrong in the following ?
>
> DECLARE_MUTEX(sem);
For the producer/consumer case, you want to initialize the semaphore to
0, not 1 which DECLARE_MUTEX(sem) does. So I would use
__DECLARE_SEMAPHORE_GENERIC(sem, 0)
The count is then the number of items produced but not yet consumed.
> producer() {
> /* One item produced */
> up(&sem);
> }
>
> consumer() {
> /* Let's wait for 10 items */
> atomic_set(&sem->count, -10);
>
> /* This starts the producers, they will call producer()
> some time in the future */
> start_producers();
>
> /* Wait for completion */
> down(&sem);
> }
Then consumer could be:
consumer()
{
int i;
start_producers();
/* Wait for 10 items to be produced */
for (i = 0; i < 10; i++)
down(&sem);
}
Nigel Gamble nigel@nrg.org
Mountain View, CA, USA. http://www.nrg.org/
MontaVista Software nigel@mvista.com
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:22 EST