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

[Rémi Denis-Courmont]

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;
>-- 
>2.17.1
>
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