implement trylock

src/sync/mutex.go

@@ -32,9 +32,21 @@ func (m *Mutex) Unlock() {
 	// Wake up a blocked task, if applicable.
 	if t := m.blocked.Pop(); t != nil {
 		scheduleTask(t)
-	} else {
-		m.locked = false
 	}
+	m.locked = false
+}
+
+// TryLock tries to lock m and reports whether it succeeded.
+//
+// Note that while correct uses of TryLock do exist, they are rare,
+// and use of TryLock is often a sign of a deeper problem
+// in a particular use of mutexes.
+func (m *Mutex) TryLock() bool {
+	if m.locked {
+		return false
+	}
+	m.Lock()
+	return true
 }
 
 type RWMutex struct {