f451a318bb
Remove unnecessary race.Release annotation from Unlock. For RWMutex we want to establish the following happens-before (HB) edges: 1. Between Unlock and the subsequent Lock. 2. Between Unlock and the subsequent RLock. 3. Between batch of RUnlock's and the subsequent Lock. 1 is provided by Release(&rw.readerSem) in Unlock and Acquire(&rw.readerSem) in Lock. 2 is provided by Release(&rw.readerSem) in Unlock and Acquire(&rw.readerSem) in RLock. 3 is provided by ReleaseMerge(&rw.writerSem) in RUnlock in Acquire(&rw.writerSem) in Lock, since we want to establish HB between a batch of RUnlock's this uses ReleaseMerge instead of Release. Release(&rw.writerSem) in Unlock is simply not needed. FWIW this is also how C++ tsan handles mutexes, not a proof but at least something. Making 2 implementations consistent also simplifies any kind of reasoning against both of them. Since this only affects performance, a reasonable test is not possible. Everything should just continue to work but slightly faster. Credit for discovering this goes to Jamie Liu. Change-Id: Ice37d29ecb7a5faed3f7781c38dd32c7469b2735 Reviewed-on: https://go-review.googlesource.com/120495 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> |
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