[PATCH 3/5] amstream: Add a second critical section for filter methods that are called from streams.

[Anton Baskanov]

On среда, 7 апреля 2021 г. 22:27:33 +07 you wrote:
> On 4/6/21 1:04 PM, Anton Baskanov wrote:
> > Signed-off-by: Anton Baskanov <baskanov at gmail.com>
> > ---
> > This is required to avoid deadlocks, e.g. when the filter is stopped
> > while EndOfStream is being called.
> 
> So, if I understand correctly, the race is:
> 
> 
> Main thread			Streaming thread
> ------------------------------------------------
> IMediaControl::Stop()		IPin::EndOfStream()
> lock graph->cs		IMediaStreamFilter::EndOfStream()
> stop parser filter
> wait for streaming thread	try to grab graph->cs
> 
> 
> Shouldn't patch 0005 be enough to avoid this? We don't hold filter->cs,
> or any amstream-specific locks, while waiting for streaming threads to stop.

Actually, the deadlock is:

Main thread			Streaming thread
------------------------------------------------
IMediaStreamFilter::Stop()		IPin::EndOfStream()
lock filter->cs		lock stream->cs
IAMMediaStream::SetState()	IMediaStreamFilter::EndOfStream()
try to lock stream->cs		try to lock filter->cs

In theory, it should be possible to move SetState() calls out of the filter 
critical section, but there are other possible deadlocks, like:

Main thread			Streaming thread
------------------------------------------------
IMediaStreamFilter::GetStopPosition()	IPin::EndOfStream()
lock filter->cs		lock stream->cs
get_seeking()
IPin_ConnectedTo()		IMediaStreamFilter::EndOfStream()
try to lock stream->cs		try to lock filter->cs