LibCore+LibThreading: Add a thread-safe weak link for EventLoop #7039
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Since the event loop has a very specifically scoped lifetime, we can't ensure that it outlives threads that hold a reference to it without blocking the thread that owns it. In order to make threads use the event loop safely, we now have an atomically ref-counted EventLoopWeak class that can be passed off to threads to safely post events/callbacks to it. Another possibility was to use an RWLock per event loop that each thread holds a read lock on, while ~EventLoop() uses a write lock to block and prevent it being destroyed until all its threads exit. However, media data providers don't receive a signal to exit due to the GC heap being intentionally leaked, so the process never actually exits. It would be possible to specifically drop the reference to PlaybackManager in HTMLMediaElement in order to make those data providers die on their own, but that doesn't help prevent this problem in other cases where it may arise.
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Looks like the changes to BackgroundThread are causing a rare deadlock (or more likely infinite spin) in some test webviews, I'll have to do some further investigation... |
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Since the event loop has a very specifically scoped lifetime, we can't ensure that it outlives threads that hold a reference to it without blocking the thread that owns it. In order to make threads use the event loop safely, we now have an atomically ref-counted EventLoopWeak class that can be passed off to threads to safely post events/callbacks to it.
Another possibility was to use an RWLock per event loop that each thread holds a read lock on, while ~EventLoop() uses a write lock to block and prevent it being destroyed until all its threads exit. However, media data providers don't receive a signal to exit due to the GC heap being intentionally leaked, so the process never actually exits. It would be possible to specifically drop the reference to PlaybackManager in HTMLMediaElement in order to make those data providers die on their own, but that doesn't help prevent this problem in other cases where it may arise.