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[Concurrency] Avoid de-escalating a task when racing to escalate. #80319

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Merged
mikeash merged 1 commit into from
Mar 27, 2025
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[Concurrency] Avoid de-escalating a task when racing to escalate. #80319

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3 changes: 3 additions & 0 deletions stdlib/public/Concurrency/TaskStatus.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1139,6 +1139,9 @@ static swift_task_escalateImpl(AsyncTask *task, JobPriority newPriority) {
auto newStatus = oldStatus;

while (true) {
// Ensure oldPriority is up to date if we retry the compare_exchange.
oldPriority = oldStatus.getStoredPriority();
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@jamieQ jamieQ Mar 27, 2025

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@mikeash small nit/question here – do we still need to read the priority on L1138 after this change?

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@mikeash mikeash Mar 27, 2025

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We don't, but it feels weird to leave it uninitialized and that's a good enough initial value. The optimizer will eliminate the redundant read for us anyway.


// Fast path: check that the stored priority is already at least
// as high as the desired priority.
if (oldPriority >= newPriority) {
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