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sync: document RWMutex locks cannot be upgraded / downgraded 

Fixes #38859

Change-Id: I9f4f6fa4cb529aaadfb3812e3a5c0da982a95f68
Reviewed-on: https://go-review.googlesource.com/c/go/+/633415
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
This commit is contained in:
Sean Liao 2024-12-03 22:41:38 +00:00 committed by Gopher Robot
parent 2a0aeb1234
commit bc0406333f
1 changed files with 2 additions and 0 deletions
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2
src/sync/rwmutex.go
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@ -24,6 +24,8 @@ import (
// the writer has acquired (and released) the lock, to ensure that
// the lock eventually becomes available to the writer.
// Note that this prohibits recursive read-locking.
// A [RWMutex.RLock] cannot be upgraded into a [RWMutex.Lock],
// nor can a [RWMutex.Lock] be downgraded into a [RWMutex.RLock].
//
// In the terminology of [the Go memory model],
// the n'th call to [RWMutex.Unlock] “synchronizes before” the m'th call to Lock