[vlc-devel] [PATCH 2/2] Wait-free snapshot handling in the vout thread

[Rémi Denis-Courmont]

Using vlc_mutex_trylock(), we make sure that the video output thread
will not yield because of an incomplete snapshot request.

---
 src/video_output/video_output.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/video_output/video_output.c b/src/video_output/video_output.c
index 27aad54..e12e033 100644
--- a/src/video_output/video_output.c
+++ b/src/video_output/video_output.c
@@ -1191,11 +1191,13 @@ static void* RunThread( void *p_this )
             p_filtered_picture = filter_chain_VideoFilter( p_vout->p->p_vf2_chain,
                                                            p_picture );
 
-        /* FIXME it is ugly that b_snapshot is not locked but I do not
-         * know which lock to use (here and in the snapshot callback) */
-        vlc_mutex_lock( &p_vout->p->snapshot.lock );
-        const bool b_snapshot = p_vout->p->snapshot.i_request > 0 && p_picture != NULL;
-        vlc_mutex_unlock( &p_vout->p->snapshot.lock );
+        bool b_snapshot = false;
+        if( vlc_mutex_trylock( &p_vout->p->snapshot.lock ) )
+        {
+             b_snapshot = p_vout->p->snapshot.i_request > 0
+                       && p_picture != NULL;
+             vlc_mutex_unlock( &p_vout->p->snapshot.lock );
+        }
 
         /*
          * Check for subpictures to display
@@ -1215,9 +1217,9 @@ static void* RunThread( void *p_this )
         /*
          * Take a snapshot if requested
          */
-        if( p_directbuffer && b_snapshot )
+        if( p_directbuffer && b_snapshot
+         && vlc_mutex_trylock( &p_vout->p->snapshot.lock ) )
         {
-            vlc_mutex_lock( &p_vout->p->snapshot.lock );
             assert( p_vout->p->snapshot.i_request > 0 );
             while( p_vout->p->snapshot.i_request > 0 )
             {
-- 
1.6.2