[vlc-devel] [RFC] vdpau/instance: create the vdp/device under lock

[Steve Lhomme]

Isn't the mutex there to protect using the same resource multiple times 
? So I don't see why it doesn't actually protect the resource creation 
itself. In the current code the same resource is created twice and 
destroyed if created twice (with what side effects ?).

On 2019-11-27 16:57, Rémi Denis-Courmont wrote:
> Reentrancy is the reason IIRC.
> 
> Le 27 novembre 2019 13:48:14 GMT+02:00, Steve Lhomme <robux4 at ycbcr.xyz> 
> a écrit :
> 
>     There's no reason to unlock before creating more than 1 instance and then
>     destroying the extra ones. No matter what we'll still return only after
>     an instance has been created (or failed to be created). Concurrent calls
>     for the same display name will only create one instance.
>     ------------------------------------------------------------------------
>       modules/hw/vdpau/instance.c | 21 ++++++---------------
>       1 file changed, 6 insertions(+), 15 deletions(-)
> 
>     diff --git a/modules/hw/vdpau/instance.c b/modules/hw/vdpau/instance.c
>     index 4a6d27fe5f0..862e63e0e21 100644
>     --- a/modules/hw/vdpau/instance.c
>     +++ b/modules/hw/vdpau/instance.c
>     @@ -129,7 +129,7 @@ static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
>       VdpStatus vdp_get_x11(const char *display_name, int snum,
>                             vdp_t **restrict vdpp, VdpDevice *restrict devicep)
>       {
>     -    vdp_instance_t *vi, *vi2;
>     +    vdp_instance_t *vi;
>       
>           if (display_name == NULL)
>           {
>     @@ -140,29 +140,20 @@ VdpStatus vdp_get_x11(const char *display_name, int snum,
>       
>           pthread_mutex_lock(&lock);
>           vi = vdp_instance_lookup(display_name, snum);
>     -    pthread_mutex_unlock(&lock);
>           if (vi != NULL)
>               goto found;
>       
>           vi = vdp_instance_create(display_name, snum);
>           if (vi == NULL)
>     -        return VDP_STATUS_ERROR;
>     -
>     -    pthread_mutex_lock(&lock);
>     -    vi2 = vdp_instance_lookup(display_name, snum);
>     -    if (unlikely(vi2 != NULL))
>     -    {   /* Another thread created the instance (race condition corner case) */
>     -        pthread_mutex_unlock(&lock);
>     -        vdp_instance_destroy(vi);
>     -        vi = vi2;
>     -    }
>     -    else
>           {
>     -        vi->next = list;
>     -        list = vi;
>               pthread_mutex_unlock(&lock);
>     +        return VDP_STATUS_ERROR;
>           }
>     +
>     +    vi->next = list;
>     +    list = vi;
>       found:
>     +    pthread_mutex_unlock(&lock);
>           *vdpp = vi->vdp;
>           *devicep = vi->device;
>           return VDP_STATUS_OK;
> 
> 
> -- 
> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser 
> ma brièveté.
> 
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