[🍒 5.9] Fix main executor check in startOnMainActor #65272
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startOnMainActor checked the current executor directly, which in some cases came back as a `nullptr`. This happens with older API which don't know to set the current executor. `swift_task_isCurrentExecutor` knows how to check for the current dispatch queue and the main thread though, so switching the main-executor check to use that API instead.
Adding discardableResult to startOnMainActor
etcwilde
added
concurrency
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@swift-ci please test |
DougGregor
approved these changes
Apr 19, 2023
ktoso
approved these changes
Apr 19, 2023
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@swift-ci please test macOS |
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Cherry-picking #65271
Explanation: Some API's don't set the current executor resulting in the current executor containing a
nullptridentity. This caused the MainExecutor check inswift_task_startOnMainActorImplto fail, when we were running on the main thread and executing off of the main dispatch queue.swift_task_isCurrentExecutorcontains additional logic to properly handle this case, checking that we're running off of the main dispatch queue and that we're running on the main thread. Also adding @discardableResult since we can discard the results from this SPI, like withTask.detached.Scope: The
swift_task_startOnMainActorImplis only used by theTask.startOnMainActorSPI, so this change only impacts the one SPI function. It's replacing a piece of logic with a function that has been in the runtime for two years now, and is in use in other places in the concurrency runtime for this purpose.Risk: Low. The SPI was added earlier this release so changing this shouldn't break existing code. Additionally, it's SPI.
rdar://108221645
rdar://108222007