1 files changed, 61 insertions, 0 deletions
diff --git a/libgo/go/sync/mutex.go b/libgo/go/sync/mutex.go
new file mode 100644
index 000000000..9a2bb2bb4
--- /dev/null
+++ b/libgo/go/sync/mutex.go
@@ -0,0 +1,61 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// 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.
+package sync
+
+import "runtime"
+
+func cas(val *uint32, old, new uint32) bool
+
+// 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
+	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")
+}
+
+// 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 {
+		// changed from 0 to 1; we hold lock
+		return
+	}
+	runtime.Semacquire(&m.sema)
+}
+
+// Unlock unlocks m.
+// It is a run-time error if m is not locked on entry to Unlock.
+//
+// A locked Mutex is not associated with a particular goroutine.
+// 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 {
+		// changed from 1 to 0; no contention
+		return
+	}
+	runtime.Semrelease(&m.sema)
+}