[EXTERNAL] Lock RateLimiter.shouldProceed() entirely to avoid race conditions #4635
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facumenzella
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Jan 7, 2025
As suggested by @facumenzella Co-authored-by: Facundo Menzella <[email protected]>
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Hi @nguyenhuy, thanks a lot for your contribution! It makes a lot of sense. I'll make sure it gets merged! |
JayShortway
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@JayShortway: That was fast! ❤️ |
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…nditions (#4635) via @nguyenhuy (#4637) * [EXTERNAL] Lock RateLimiter.shouldProceed() entirely to avoid race conditions (#4635) * Lock RateLimiter.shouldProceed() entirely to avoid race conditions Android does this as well: https://github.com/RevenueCat/purchases-android/blob/eb3c8f4aa1a6993f12d6e2f93cc82d26063101a6/purchases/src/main/kotlin/com/revenuecat/purchases/utils/RateLimiter.kt#L10 * Fix typo in RateLimiterTests' file name * Update Sources/Misc/RateLimiter.swift As suggested by @facumenzella Co-authored-by: Facundo Menzella <[email protected]> --------- via @nguyenhuy * Update Sources/Misc/RateLimiter.swift via @nguyenhuy Co-authored-by: Huy Nguyen <[email protected]> --------- Co-authored-by: Huy Nguyen <[email protected]>
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Checklist
purchases-androidand hybridsMotivation
Introduced in #3709,
RateLimiteris used exclusively byPurchases.syncAttributesAndOfferingsIfNeeded(completion:). The documentation of this method doesn't mention any threading requirement, so it's reasonable to assume that it can be called on any thread. This meansRateLimiterneeds to be thread safe, otherwise clients will run into race conditions as reported in #4440.Description
Fortunately the
RateLimiterclass is quite simple.Its contants don't need to be atomic/locked since they are thread safe by definition. Turning
timestampsandindexvars into atomics doesn't help much in this case becauseshouldProceed()needs multiple reads and writes in a "transaction".Using a
Lockto wrap the whole method is the simplest and self-contained approach so I picked it. Android is doing the same thing (here).The lock is a non-recursive lock because there is no need for reentrant. And in principle I avoid recursive locks as much as possible since one can easily lose control over the locks, especially in more complicated use cases/codebases. This is a big problem that we have had for a long time in AsyncDisplayKit/Texture.
Unit tests remain the same because testing for race conditions is rather difficult and unpredictable. Texture has a bunch of thrash tests that kind of work but not 100%. Since the subject under test in this case is rather simple and the fix is straightforward it should work. Otherwise, we can have follow up PRs for both iOS and Android.
This should resolve #4440.
This PR also renames
RateLimiterRests.swifttoRateLimiterTests.swift.