v4l2decoder: Track pending request

With the asynchronous slice decoding, we only queue up to 2 slices
per frames. That side effect is that now we are dequeuing bitstream
buffers in both decoding and presentation order. This would lead to
a bitstream buffer from a previous frame being dequeued instead of
the expected last slice buffer and lead to us trying to queue an
already queued bitstream buffer.

We now fix this by tracking pending requests. As request are executed
in decoding order, we marking a request done, we can effectively
dequeue bitstream buffer from all previous request, as they have been
executed already.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1395>

1 files changed, 38 insertions, 3 deletions

diff --git a/sys/v4l2codecs/gstv4l2decoder.c b/sys/v4l2codecs/gstv4l2decoder.c
index d00706eec..fad7d7485 100644
--- a/sys/v4l2codecs/gstv4l2decoder.c
+++ b/sys/v4l2codecs/gstv4l2decoder.c
@@ -63,6 +63,7 @@ struct _GstV4l2Decoder
   gint media_fd;
   gint video_fd;
   GstQueueArray *request_pool;
+  GstQueueArray *pending_requests;
 
   enum v4l2_buf_type src_buf_type;
   enum v4l2_buf_type sink_buf_type;
@@ -104,6 +105,7 @@ static void
 gst_v4l2_decoder_init (GstV4l2Decoder * self)
 {
   self->request_pool = gst_queue_array_new (16);
+  self->pending_requests = gst_queue_array_new (16);
 }
 
 static void
@@ -223,8 +225,18 @@ gst_v4l2_decoder_streamon (GstV4l2Decoder * self, GstPadDirection direction)
 gboolean
 gst_v4l2_decoder_streamoff (GstV4l2Decoder * self, GstPadDirection direction)
 {
-  gint ret;
+  GstV4l2Request *pending_req;
   guint32 type = direction_to_buffer_type (self, direction);
+  gint ret;
+
+  if (direction == GST_PAD_SRC) {
+    /* STREAMOFF have the effect of cancelling all requests and unqueuing all
+     * buffers, so clear the pending request list */
+    while ((pending_req = gst_queue_array_pop_head (self->pending_requests))) {
+      g_clear_pointer (&pending_req->bitstream, gst_memory_unref);
+      pending_req->pending = FALSE;
+    }
+  }
 
   ret = ioctl (self->video_fd, VIDIOC_STREAMOFF, &type);
   if (ret < 0) {
@@ -838,7 +850,14 @@ gst_v4l2_request_free (GstV4l2Request * request)
   request->decoder = NULL;
 
   if (request->pending) {
+    gint idx;
+
     GST_DEBUG_OBJECT (decoder, "Freeing pending request %p.", request);
+
+    idx = gst_queue_array_find (decoder->pending_requests, NULL, NULL);
+    if (idx >= 0)
+      gst_queue_array_drop_element (decoder->pending_requests, idx);
+
     gst_v4l2_request_free (request);
     g_object_unref (decoder);
     return;
@@ -874,6 +893,7 @@ gst_v4l2_request_queue (GstV4l2Request * request)
   }
 
   request->pending = TRUE;
+  gst_queue_array_push_tail (request->decoder->pending_requests, request);
 
   return TRUE;
 }
@@ -888,8 +908,23 @@ void
 gst_v4l2_request_set_done (GstV4l2Request * request)
 {
   if (request->bitstream) {
-    gst_v4l2_decoder_dequeue_sink (request->decoder);
-    g_clear_pointer (&request->bitstream, gst_memory_unref);
+    GstV4l2Decoder *dec = request->decoder;
+    GstV4l2Request *pending_req;
+
+    while ((pending_req = gst_queue_array_pop_head (dec->pending_requests))) {
+      gst_v4l2_decoder_dequeue_sink (request->decoder);
+      g_clear_pointer (&pending_req->bitstream, gst_memory_unref);
+
+      if (pending_req == request)
+        break;
+    }
+
+    /* Pending request should always be found in the fifo */
+    if (pending_req != request) {
+      g_warning ("Pending request not found in the pending list.");
+      gst_v4l2_decoder_dequeue_sink (request->decoder);
+      g_clear_pointer (&pending_req->bitstream, gst_memory_unref);
+    }
   }
 
   request->pending = FALSE;