[PATCH] winegstreamer: Do not block forever if EOS races with command queue.

[Giovanni Mascellani]

Hi,

Il 08/02/22 18:50, Zebediah Figura ha scritto:
> I'm having a hard time understanding the race here. Can wait_on_sample() 
> be called multiple times concurrently for the same stream? If not I 
> don't see how it can race with itself.

Consider this flow:
  * RequestSample() is called: it checks that the stream is not EOS and 
queues SOURCE_ASYNC_REQUEST_SAMPLE;
  * while SOURCE_ASYNC_REQUEST_SAMPLE is in the queue, RequestSample() 
is called again, and another SOURCE_ASYNC_REQUEST_SAMPLE is queued;
  * the first SOURCE_ASYNC_REQUEST_SAMPLE is executed and 
wait_on_sample() is called; wg_parser_stream_get_event() happens to find 
stream->event of type WG_PARSER_EVENT_EOS; it returns that event and 
reset the event to WG_PARSER_EVENT_NONE; consequently wait_on_sample() 
issues a MEEndOfStream event;
  * the second SOURCE_ASYNC_REQUEST_SAMPLE is executed and 
wait_on_sample() is called; wg_parser_stream_get_event() sees the stream 
event set to WG_PARSER_EVENT_NONE, and it will never change, therefore 
it waits forever.

The problem is that the EOS condition must be rechecked inside 
wh_parser_stream_get_event(), because last time it was checked (in 
RequestSample()) might be out-of-date.

Does this make sense?

Thanks, Giovanni.