[ASImageNode] Fix a threading issue which can cause a display completion block to never be executed #1148
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Member
nguyenhuy
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Sep 28, 2018
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nguyenhuy
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- Clear _displayCompletionBlock while we still have the node's instance lock. Because it may not be the same block by the time the lock is reacquired. In other words, it can happen that another thread sets a new display block after this thread releases the lock but before it reacquires it. And we don't want to clear out the new block.
- Reduce a lock/unlock pair which should help perf a tiny bit.
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Oct 21, 2018
| if (shouldPerformDisplayCompletionBlock) { | ||
| _displayCompletionBlock = nil; | ||
| } | ||
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| BOOL hasDebugLabel = (_debugLabelNode != nil); |
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Since many of the calls in the debug label section require the lock anyway (like self.bounds), should we just continue holding the lock until after that?
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There's a comment below stating that we don't care about locking in the debug section. I don't remember the reasoning behind that (locking violation somehow?), but let's revisit it in another PR.
CHANGELOG.md
Outdated
| @@ -57,6 +57,7 @@ | |||
| - Clean up timing of layout tree flattening/ copying of unflattened tree for Weaver. [Michael Zuccarino](https://github.com/mikezucc) [#1157](https://github.com/TextureGroup/Texture/pull/1157) | |||
| - Fix crash setting attributed text on multiple threads [Michael Schneider](https://github.com/maicki) | |||
| - [ASTextNode2] Ignore certain text alignments while calculating intrinsic size [Huy Nguyen](https://github.com/nguyenhuy) [#1166](https://github.com/TextureGroup/Texture/pull/1166) | |||
| - [ASImageNode] Fix a threading issue which can cause a display completion block to never be executed. [Huy Nguyen](https://github.com/nguyenhuy) [#1148](https://github.com/TextureGroup/Texture/pull/1148) | |||
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From the header file, it isn't too clear that calling the method multiple times will overwrite the previous block without calling it. In order to guarantee balanced calls, we'd probably need to track them with an array.
This seems like an increasingly common case in the framework (even interfaceStateDelegates now), so it might be worth creating a helper class like ASBlockList / ASBlockQueue to manage efficiently. Not important right now, just an idea.
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Agree that it'd be nice to have track all blocks in an array.
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…ode's instance lock - Because it may not be the same block by the time the lock is reacquired. In other words, it can happen that another thread sets a new display block after this thread releases the lock but before it reacquires it. And we don't want to clear out the new block. - Reduce a lock/unlock pair which should help perf a tiny bit.
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…tion block to never be executed (TextureGroup#1148) - Clear _displayCompletionBlock while we still have the node's instance lock. Because it may not be the same block by the time the lock is reacquired. In other words, it can happen that another thread sets a new display block after this thread releases the lock but before it reacquires it. And we don't want to clear out the new block. - Reduce a lock/unlock pair which should help perf a tiny bit.
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