[SoruceKit] Audit SwiftASTManager to prevent deadlocks #58978
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That's a lot of mutexes, locks, and queues 😓 Changes seem reasonable to me, but in general this feels somewhat fragile. I do wonder if such fine grained locking is really worth it in these cases but since we already have it 🤷 |
bnbarham
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Jun 22, 2023
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- Ensure that no callbacks are called when either of these mutexes are held:
- `SwiftASTConsumer::CancellationRequestCallbackAndIsCancelledMtx`
- `ASTBuildOperation::DependencyStampsMtx`
- Exception: We allow calls to `getBuferStamp` because that doesn’t claim any locks)
- No change was necessary here
- `ASTBuildOperation::ConsumersAndResultMtx`
- `ASTBuildOperation::CacheMtx`
- No change was necessary here
- `ASTBuildOperation::ScheduledConsumersMtx`
- Make sure we always inform the consumers asynchronously, even if the operation was already cancelled when the consumer got enqueued by introducing `ConsumerNotificationQueue`
- Ensure that all callbacks to `SwiftASTConsumer` (i.e. `requestCancellation` and `handlePrimaryAST`, `failed`, `cancelled`) are performed asyncronously from a queue to avoid deadlocks
rdar://110357502
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rintaro
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After fixing #42258, I re-audited
SwiftASTManagerto prevent any further deadlocks by further narrowing locks scopes and making sure that some callbacks are always called from a background queue that can’t have claimed any locks.SwiftASTConsumer::CancellationRequestCallbackAndIsCancelledMtxASTBuildOperation::DependencyStampsMtxgetBuferStampbecause that doesn’t claim any locks)ASTBuildOperation::ConsumersAndResultMtxASTBuildOperation::CacheMtxASTBuildOperation::ScheduledConsumersMtxConsumerNotificationQueueSwiftASTConsumer(i.e.requestCancellationandhandlePrimaryAST,failed,cancelled) are performed asyncronously from a queue to avoid deadlocksrdar://110357502