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runtime: record mutex event before readying

Currently, semrelease1 readies the next waiter before recording a
mutex event. However, if the next waiter is expecting to look at the
mutex profile, as is the case in TestMutexProfile, this may delay
recording the event too much.

Swap the order of these operations so semrelease1 records the mutex
event before readying the next waiter. This also means readying the
next waiter is the very last thing semrelease1 does, which seems
appropriate.

Fixes #19139.

Change-Id: I1a62063599fdb5d49bd86061a180c0a2d659474b
Reviewed-on: https://go-review.googlesource.com/45751
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Austin Clements 2017-06-14 11:07:24 -04:00
parent 738739f565
commit b067ad939d
2 changed files with 7 additions and 4 deletions

View File

@ -542,6 +542,10 @@ func blockMutex() {
time.Sleep(blockDelay) time.Sleep(blockDelay)
mu.Unlock() mu.Unlock()
}() }()
// Note: Unlock releases mu before recording the mutex event,
// so it's theoretically possible for this to proceed and
// capture the profile before the event is recorded. As long
// as this is blocked before the unlock happens, it's okay.
mu.Lock() mu.Lock()
} }
@ -560,7 +564,6 @@ func blockCond() {
} }
func TestMutexProfile(t *testing.T) { func TestMutexProfile(t *testing.T) {
testenv.SkipFlaky(t, 19139)
old := runtime.SetMutexProfileFraction(1) old := runtime.SetMutexProfileFraction(1)
defer runtime.SetMutexProfileFraction(old) defer runtime.SetMutexProfileFraction(old)
if old != 0 { if old != 0 {

View File

@ -182,6 +182,9 @@ func semrelease1(addr *uint32, handoff bool) {
unlock(&root.lock) unlock(&root.lock)
if s != nil { // May be slow, so unlock first if s != nil { // May be slow, so unlock first
acquiretime := s.acquiretime acquiretime := s.acquiretime
if acquiretime != 0 {
mutexevent(t0-acquiretime, 3)
}
if s.ticket != 0 { if s.ticket != 0 {
throw("corrupted semaphore ticket") throw("corrupted semaphore ticket")
} }
@ -189,9 +192,6 @@ func semrelease1(addr *uint32, handoff bool) {
s.ticket = 1 s.ticket = 1
} }
readyWithTime(s, 5) readyWithTime(s, 5)
if acquiretime != 0 {
mutexevent(t0-acquiretime, 3)
}
} }
} }