diff options
Diffstat (limited to 'src/pkg/sync/mutex.go')
| -rw-r--r-- | src/pkg/sync/mutex.go | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/src/pkg/sync/mutex.go b/src/pkg/sync/mutex.go index c4d82af00..2a1270b9c 100644 --- a/src/pkg/sync/mutex.go +++ b/src/pkg/sync/mutex.go @@ -3,10 +3,10 @@ // license that can be found in the LICENSE file. // The sync package provides basic synchronization primitives -// such as mutual exclusion locks. Other than the Once type, -// most are intended for use by low-level library routines. -// Higher-level synchronization is better done via channels -// and communication. +// such as mutual exclusion locks. Other than the Once and +// WaitGroup types, most are intended for use by low-level +// library routines. Higher-level synchronization is better +// done via channels and communication. package sync import "runtime" @@ -53,9 +53,14 @@ func (m *Mutex) Lock() { // It is allowed for one goroutine to lock a Mutex and then // arrange for another goroutine to unlock it. func (m *Mutex) Unlock() { - if xadd(&m.key, -1) == 0 { + switch v := xadd(&m.key, -1); { + case v == 0: // changed from 1 to 0; no contention return + case int32(v) == -1: + // changed from 0 to -1: wasn't locked + // (or there are 4 billion goroutines waiting) + panic("sync: unlock of unlocked mutex") } runtime.Semrelease(&m.sema) } |