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Re: [libvirt] [PATCH] threadpool: Don't wait on condition if pool has no workers



On 12/09/2011 07:26 AM, Michal Privoznik wrote:
> Pool creates new workers dynamically. However, it is possible
> for a pool to have no workers. If we want to free that pool,
> we don't want to wait on quit condition as it will never be
> signaled.
> ---
> Pushing under trivial rule
> 
>  src/util/threadpool.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/src/util/threadpool.c b/src/util/threadpool.c
> index c16e2af..883d1e5 100644
> --- a/src/util/threadpool.c
> +++ b/src/util/threadpool.c
> @@ -258,7 +258,8 @@ void virThreadPoolFree(virThreadPoolPtr pool)
>          virCondBroadcast(&pool->prioCond);
>      }
>  
> -    ignore_value(virCondWait(&pool->quit_cond, &pool->mutex));
> +    if (pool->nWorkers > 0 || pool->nPrioWorkers > 0)
> +        ignore_value(virCondWait(&pool->quit_cond, &pool->mutex));

Shouldn't this be a while loop, instead of an if()?  That is, the
documentation for pthread_cond_wait (which is what virCondWait uses
under the hood) says that any robust implementation must be ready for
spurious wakeups, and must re-check the condition and loop until the
condition has been met (here, the condition we want is that all workers
must have exited prior to us continuing).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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