[6.4] AsyncQueue: await dependencies concurrently to avoid priority inversion#58
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ktoso merged 1 commit intoMay 28, 2026
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A sequentially-awaited list of dependency tasks only propagates a priority escalation to the dependency currently being awaited. The rest stay at their original priority and can starve under load, producing nondeterministic multi-minute hangs in tests that mix self-serializing and non-self-serializing metadata (e.g. a serial task waiting on many concurrent tasks). Replace the sequential await with concurrentForEach so a priority escalation on the running task reaches every dependency at once. Speculative fix for rdar://178006261 (cherry picked from commit 24bfcfd)
rintaro
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hamishknight
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May 27, 2026
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only failure: using build wrangler powers to merge. |
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Cherry-pick #57 into
release/6.4.xfor ... await dep.task.waitForCompletion()loop inAsyncQueue.swiftwithdependencies.concurrentForEach { ... }. Functionally equivalent for the dependency tasks themselves (which already run concurrently), but the await fan-out changes so that a priority escalation on the awaiting task propagates to every dependency at once instead of only the one currently being awaited.AsyncQueueis used for (indexing, request handling).