[6.0][Concurrency] Defensive copying of tasks locals in TaskGroups (rather than crashing) #74038
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@swift-ci please test |
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Minor follow up from |
…roups fix C++11 warning about char* conversion remove free(message) since message is not dynamically allocated anymore fix embedded swift error reporting task-local abuse in group cleanup: remove unrecognized clang ide diagnostic options These are something CLion understands and suggests, but yeah let's avoid having warnings in the build. [Concurrency] Implement only-when-necessary defensive TL copying in in task groups [Concurrency] Correct handling of mixed nested values minor cleanups and renames [Concurrency] Simplify task locals destroy; add more tests for locals add extra test
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@swift-ci please test |
DougGregor
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Jun 3, 2024
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Short description: (very detailed discussion/description in #73978)
Previously a specific nesting of
withTaskGroup { group in $taskLocal.withValue() { group.addTask {} } }was forced to defensively crash in order to prevent the child task wrongly directly linking to the parent's memory (which would be popped when the withValue returned, but the child task was still running).We detected this situation to keep memory safety however this situation can happen in real situations and has caused e.g. swift-testing issues and workarounds.
Instead we are now copying this specific kind of "risky" value such that the pattern can be properly supported, without any user intervention. This expands the range of accepted not-crashing-at-runtime code using swift concurrency.
Result: Instead of crashing, we now can support this pattern - which sometimes comes up unbeknownst to actual developers, because they may be using libraries which wrap them in task groups and whatnot.
Scope/Impact: Expands the range of not-crashing code using task-locals and task groups in combination. A specific pattern which was previously banned is now allowed.
Risk: Low, memory management is tricky but carefully maintained using task local allocations. Testing covers all scenarios which could have been affected.
Testing: CI testing, added more tests to cover specific scenarios. Removed tests are those which "expected a crash".
Review: @DougGregor
Original PR: #73978 including review-follow-up #74089
Radar: rdar://127156303