commit c55516dd554dafc106fbbd1f16062dd1a8173c56
author Henrik Boström <hbos@webrtc.org> Mon May 11 14:29:22 2020
committer Commit Bot <commit-bot@chromium.org> Mon May 11 20:35:30 2020
tree 554147404739e65f8b50dc95674a21cb5196c983
parent cc57b935cdd19bc78352ab7e3091b2b3ad653074

[Adaptation] Make Resources reference counted and add more DCHECKs.

In a future CL, adaptation processing and stream encoder resource
management will happen on different task queues. When this is the case,
asynchronous tasks will be posted in both directions and some resources
will have internal states used on multiple threads.

This CL makes the Resource class reference counted in order to support
posting tasks to a different threads without risk of use-after-free
when a posted task is executed with a delay. This is preferred over
WeakPtr strategies because WeakPtrs are single-threaded and preferred
over raw pointer usage because the reference counted approach enables
more compile-time and run-time assurance. This is also "future proof";
when resources can be injected through public APIs, ownership needs to
be shared between libwebrtc and the application (e.g. Chrome).

To reduce the risk of making mistakes in the future CL, sequence
checkers and task queue DCHECKs are added as well as other DCHECKs to
make sure things have been cleaned up before destruction, e.g:
- Processor gets a sequence checker. It is entirely single-threaded.
- Processor must not have any attached listeners or resources on
  destruction.
- Resources must not have any listeners on destruction.
- The Manager, EncodeUsageResource and QualityScalerResource DCHECKs
  they are running on the encoder queue.
- TODOs are added illustrating where we want to add PostTasks in the
  future CL.

Lastly, upon VideoStreamEncoder::Stop() we delete the
ResourceAdaptationProcessor. Because the Processor is already used in
posted tasks, some if statements are added to ensure the Processor is
not used after destruction.

Bug: webrtc:11542, webrtc:11520
Change-Id: Ibaa8a61d86d87a71f477d1075a117c28d9d2d285
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174760
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31217}