Do not make resetting the "access" filters reset the queue itself. This
is more flexible, and will be used in a later commit.
Also, if the queue is not in the reset state while the input access
filter is reset, make it immediately request data again. This is more
consistent, because it'll enter the state it "should" be, rather when
the filter's process function is called at an (essentially) random point
in the future. This means the filter graph will resume work on its own
if the queue was not reset before filter reset.
This could affect the only current user of f_async_queue, the code for
the --vd-queue-enable/--ad-queue-enable feature in f_decoder_wrapper.
But it looks like this already uses it in a compatible way.
This is supposed to enable communication between filter graphs on
separate threads. Having multiple threads makes only sense if they can
run concurrently with each other, which requires such an asynchronous
queue as a building block. (Probably.)
The basic idea is that you have two independent filters, which can be
each part of separate filter graphs, but which communicate into one
direction with an explicit queue. This is rather similar to unix pipes.
Just like unix pipes, the queue is limited in size, so that still some
data flow control enforced, and runaway memory usage is avoided.
This implementation is pretty dumb. In theory, you could avoid avoid
waking up the filter graphs in quite a lot of situations. For example,
you don't need to wake up the consumer filter if there are already
frames queued. Also, you could add "watermarks" that set a threshold at
which producer or consumer should be woken up to produce/consume more
frames (this would generally serve to "batch" multiple frames at once,
instead of performing high-frequency wakeups). But this is hard, so the
code is dumb. (I just deleted all related code when I still got
situations where wakeups were lost.)
This is actually salvaged and modified from a much older branch I had
lying around. It will be used in the next commit.
wm4