Fix potential race condition when accessing Application.http.client.shared #2576
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…shared` accessor; the storage is a Dictionary and can potentially be mutated by one thread while being accessed from another which isn't holding the lock. This is not safe, even if the logic checks again after taking the lock. Unfortunately, this is likely to be a relatively obvious performance regression, but it's also a definitive thread safety concern.
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@weissi Can you double-check my understanding on this one? 😰 |
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@gwynne Correct, double-checked locking is not legal in Swift (and also not in most other languages). |
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These changes are now available in 4.41.3 |
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These changes are now available in 4.41.3 |
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The accessor for
Application.http.client.sharedwas performing a lookup in the storage dictionary using double-checked locking, which is not actually thread-safe (despite all appearances to the contrary). It now unconditionally takes the lock before performing the lookup.Applications making heavy use of
Request.clientorApplication.clientmay experience a performance regression from this change.