Imported Upstream version 2011.03.07.1upstream/2011.03.07.1

1 files changed, 12 insertions, 19 deletions

diff --git a/src/pkg/sync/mutex.go b/src/pkg/sync/mutex.go
index 2a1270b9c..da565d38d 100644
--- a/src/pkg/sync/mutex.go
+++ b/src/pkg/sync/mutex.go
@@ -9,37 +9,30 @@
 // done via channels and communication.
 package sync
 
-import "runtime"
-
-func cas(val *uint32, old, new uint32) bool
+import (
+	"runtime"
+	"sync/atomic"
+)
 
 // A Mutex is a mutual exclusion lock.
 // Mutexes can be created as part of other structures;
 // the zero value for a Mutex is an unlocked mutex.
 type Mutex struct {
-	key  uint32
+	key  int32
 	sema uint32
 }
 
-// Add delta to *val, and return the new *val in a thread-safe way. If multiple
-// goroutines call xadd on the same val concurrently, the changes will be
-// serialized, and all the deltas will be added in an undefined order.
-func xadd(val *uint32, delta int32) (new uint32) {
-	for {
-		v := *val
-		nv := v + uint32(delta)
-		if cas(val, v, nv) {
-			return nv
-		}
-	}
-	panic("unreached")
+// A Locker represents an object that can be locked and unlocked.
+type Locker interface {
+	Lock()
+	Unlock()
 }
 
 // Lock locks m.
 // If the lock is already in use, the calling goroutine
 // blocks until the mutex is available.
 func (m *Mutex) Lock() {
-	if xadd(&m.key, 1) == 1 {
+	if atomic.AddInt32(&m.key, 1) == 1 {
 		// changed from 0 to 1; we hold lock
 		return
 	}
@@ -53,11 +46,11 @@ 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() {
-	switch v := xadd(&m.key, -1); {
+	switch v := atomic.AddInt32(&m.key, -1); {
 	case v == 0:
 		// changed from 1 to 0; no contention
 		return
-	case int32(v) == -1:
+	case v == -1:
 		// changed from 0 to -1: wasn't locked
 		// (or there are 4 billion goroutines waiting)
 		panic("sync: unlock of unlocked mutex")