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| author | Rhys Hiltner <rhys@justin.tv> | 2019-11-08 10:30:24 -0800 |
|---|---|---|
| committer | Brad Fitzpatrick <bradfitz@golang.org> | 2019-11-09 19:31:32 +0000 |
| commit | 7148478f1b433caa11c8827657ee1bc61f0b1c5d (patch) | |
| tree | f5c52805a13b0ba7285133891b22d5424aa059cc /src/sync | |
| parent | 6e111956ab4849976f9dcf46ecac575fa8105268 (diff) | |
| download | go-7148478f1b433caa11c8827657ee1bc61f0b1c5d.tar.gz go-7148478f1b433caa11c8827657ee1bc61f0b1c5d.zip | |
sync: yield to the waiter when unlocking a starving mutex
When we have already assigned the semaphore ticket to a specific
waiter, we want to get the waiter running as fast as possible since
no other G waiting on the semaphore can acquire it optimistically.
The net effect is that, when a sync.Mutex is contended, the code in
the critical section guarded by the Mutex gets a priority boost.
Fixes #33747
The original work was done in CL 200577 by Carlo Alberto Ferraris. The
change was reverted in CL 205817 because it broke the linux-arm64-packet
and solaris-amd64-oraclerel builders.
Change-Id: I76d79b1d63fd206ed1c57fe6900cb7ae9e4d46cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/206180
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Diffstat (limited to 'src/sync')
| -rw-r--r-- | src/sync/mutex.go | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/src/sync/mutex.go b/src/sync/mutex.go index 11ad20c975..3028552f74 100644 --- a/src/sync/mutex.go +++ b/src/sync/mutex.go @@ -216,7 +216,8 @@ func (m *Mutex) unlockSlow(new int32) { old = m.state } } else { - // Starving mode: handoff mutex ownership to the next waiter. + // Starving mode: handoff mutex ownership to the next waiter, and yield + // our time slice so that the next waiter can start to run immediately. // Note: mutexLocked is not set, the waiter will set it after wakeup. // But mutex is still considered locked if mutexStarving is set, // so new coming goroutines won't acquire it. |