Imported Upstream version 2011.03.07.1upstream/2011.03.07.1

1 files changed, 18 insertions, 5 deletions

diff --git a/src/pkg/sync/rwmutex.go b/src/pkg/sync/rwmutex.go
index 25696aca2..9248b4b03 100644
--- a/src/pkg/sync/rwmutex.go
+++ b/src/pkg/sync/rwmutex.go
@@ -4,6 +4,8 @@
 
 package sync
 
+import "sync/atomic"
+
 // An RWMutex is a reader/writer mutual exclusion lock.
 // The lock can be held by an arbitrary number of readers
 // or a single writer.
@@ -14,9 +16,9 @@ package sync
 // Writers take priority over Readers: no new RLocks
 // are granted while a blocked Lock call is waiting.
 type RWMutex struct {
-	w           Mutex  // held if there are pending readers or writers
-	r           Mutex  // held if the w is being rd
-	readerCount uint32 // number of pending readers
+	w           Mutex // held if there are pending readers or writers
+	r           Mutex // held if the w is being rd
+	readerCount int32 // number of pending readers
 }
 
 // RLock locks rw for reading.
@@ -33,7 +35,7 @@ func (rw *RWMutex) RLock() {
 	//   B: rw.RUnlock()
 	//   ... (new readers come and go indefinitely, W is starving)
 	rw.r.Lock()
-	if xadd(&rw.readerCount, 1) == 1 {
+	if atomic.AddInt32(&rw.readerCount, 1) == 1 {
 		// The first reader locks rw.w, so writers will be blocked
 		// while the readers have the RLock.
 		rw.w.Lock()
@@ -46,7 +48,7 @@ func (rw *RWMutex) RLock() {
 // It is a run-time error if rw is not locked for reading
 // on entry to RUnlock.
 func (rw *RWMutex) RUnlock() {
-	if xadd(&rw.readerCount, -1) == 0 {
+	if atomic.AddInt32(&rw.readerCount, -1) == 0 {
 		// last reader finished, enable writers
 		rw.w.Unlock()
 	}
@@ -71,3 +73,14 @@ func (rw *RWMutex) Lock() {
 // goroutine.  One goroutine may RLock (Lock) an RWMutex and then
 // arrange for another goroutine to RUnlock (Unlock) it.
 func (rw *RWMutex) Unlock() { rw.w.Unlock() }
+
+// RLocker returns a Locker interface that implements
+// the Lock and Unlock methods by calling rw.RLock and rw.RUnlock.
+func (rw *RWMutex) RLocker() Locker {
+	return (*rlocker)(rw)
+}
+
+type rlocker RWMutex
+
+func (r *rlocker) Lock()   { (*RWMutex)(r).RLock() }
+func (r *rlocker) Unlock() { (*RWMutex)(r).RUnlock() }