265096 2023-11-18 16:49:27 -0800 Provide ability to convert one type of NativePromise into another 2023-11-19 21:29:01 -0800 1 1 1 Unclassified WebKit Web Template Framework WebKit Nightly Build Unspecified Unspecified RESOLVED DUPLICATE 264028 https://bugs.webkit.org/show_bug.cgi?id=264028 https://bugs.webkit.org/show_bug.cgi?id=265102 InRadar P2 Normal --- 1 jean-yves.avenard jean-yves.avenard webkit-bug-importer oldest_to_newest 1993711 0 jean-yves.avenard 2023-11-18 16:49:27 -0800 The problem was mentioned in https://github.com/WebKit/WebKit/pull/20652#discussion_r1397622606 Where we did the following: ``` Ref<MediaPromise> SourceBufferPrivate::removeCodedFrames(const MediaTime& start, const MediaTime& end, const MediaTime& currentTime) { MediaPromise::Producer producer; Ref promise = producer.promise(); m_currentSourceBufferOperation = m_currentSourceBufferOperation->whenSettled(RunLoop::current(), [weakThis = WeakPtr { *this }, this, start, end, currentTime](auto&& result) mutable { if (!weakThis || !result) return MediaPromise::createAndReject(!result ? result.error() : PlatformMediaError::BufferRemoved); return removeCodedFramesInternal(start, end, currentTime); })->whenSettled(RunLoop::current(), [producer = WTFMove(producer)](auto&& result) mutable { producer.settle(result); return MediaPromise::createAndSettle(WTFMove(result)); }); return promise; } ``` m_currentSourceBufferOperation is a MediaPromise which is exclusive; you can only perform a single then/whenSettled on it. Exclusive promise are useful as it allows for move semantics and avoid needless copies of the resolved/rejected value. So in the code above, we can't return m_currentSourceBufferOperation as it would mean you run then/whenSettled on it twice, which would assert. One solution above would be to 1- make MediaPromise (NativePromise<void, PlatformMediaError>) a non-exclusive promise or 2- make m_currentSourceBufferOperation be a NonExclusive promise and allows to convert a non exclusive promise into an exclusive one. Doing 1- would require changing all the MediaPromise use points to no longer expect a r-valued result (most are using `(auto&& result)` as their prototype 2- allows for less disruptive code and allow for rather more elegant code. It would also be a bit more efficient as you no longer require to dispatch a task So the above could be written: ``` m_currentSourceBufferOperation = m_currentSourceBufferOperation->whenSettled(RunLoop::current(), [weakThis = WeakPtr { *this }, this, start, end, currentTime](auto&& result) mutable { if (!weakThis || !result) return OperationPromise::createAndReject(!result ? result.error() : PlatformMediaError::BufferRemoved); return static_cast<Ref<OperationPromise>>(removeCodedFramesInternal(start, end, currentTime).get()); }); return m_currentSourceBufferOperation.get(); ``` where m_currentSourceBufferOperation.get is now a non-exclusive promise. Adopting solution 2, also gets us close to achieving bug 264028 1993712 1 webkit-bug-importer 2023-11-18 16:49:41 -0800 <rdar://problem/118610126> 1993713 2 jean-yves.avenard 2023-11-18 17:06:53 -0800 Pull request: https://github.com/WebKit/WebKit/pull/20713 1993739 3 jean-yves.avenard 2023-11-19 03:28:02 -0800 Pull request: https://github.com/WebKit/WebKit/pull/20721 1993815 4 jean-yves.avenard 2023-11-19 21:29:01 -0800 Combined changes with bug 264028 *** This bug has been marked as a duplicate of bug 264028 ***