Fix Text Node Thread Sanitizer Warning #830
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Problem reported in this issue #552 |
garrettmoon
reviewed
Mar 12, 2018
Source/ASTextNode.mm
Outdated
| @@ -85,8 +88,13 @@ - (BOOL)isEqual:(ASTextNodeRendererKey *)object | |||
| if (self == object) { | |||
| return YES; | |||
| } | |||
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| // Lock both objects, avoiding deadlock. | |||
| std::lock(_m, object->_m); | |||
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Unrelated to you changes, should there be class checks in here? It may not matter in since this is an internal object, but should we ensure object is an ASTextRendererKey for correctness?
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Good call. I added a comment explaining it.
garrettmoon
approved these changes
Mar 12, 2018
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Only un-CI'd changes are a comment I added. Landing! |
bernieperez
pushed a commit
to AtomTickets/Texture
that referenced
this pull request
Apr 25, 2018
* Fix thread sanitizer warning in ASTextNodeRendererKey * Update changelog * Comment on missing class check
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I made this before I saw that #819 exists, and while I think @hebertialmeida's solution may possibly be faster (though it could lead to thread explosion), I think this solution is more precise.
The race condition is in the C++ struct
ASTextKitAttributesitself. Since there is no synchronization around the contents of that struct, the sanitizer is correctly warning us.This has led me down a heck of a rabbit-hole with memory safety. In lieu of a more general fix for the problem of creating very fast, but flexible and thread-safe C++ structures that interoperate well with Objective-C, this fix solves the thread sanitizer warnings in an appropriate way, by protecting access to that structure, at least in the
hashandisEqualmethods, which seems sufficient since the class is specifically termed aKey.Note that it's not sufficient to make the Objective-C property accessor atomic, since that seems only to protect the pointer. I don't know much about how synthesized atomic accessors treat c++ objects, but I wouldn't be surprised if they're not actually atomic.