1 files changed, 62 insertions, 0 deletions
diff --git a/src/pkg/sync/once_test.go b/src/pkg/sync/once_test.go
new file mode 100644
index 000000000..157a3667a
--- /dev/null
+++ b/src/pkg/sync/once_test.go
@@ -0,0 +1,62 @@
+// 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.
+
+package sync_test
+
+import (
+	. "sync"
+	"sync/atomic"
+	"runtime"
+	"testing"
+)
+
+type one int
+
+func (o *one) Increment() {
+	*o++
+}
+
+func run(once *Once, o *one, c chan bool) {
+	once.Do(func() { o.Increment() })
+	c <- true
+}
+
+func TestOnce(t *testing.T) {
+	o := new(one)
+	once := new(Once)
+	c := make(chan bool)
+	const N = 10
+	for i := 0; i < N; i++ {
+		go run(once, o, c)
+	}
+	for i := 0; i < N; i++ {
+		<-c
+	}
+	if *o != 1 {
+		t.Errorf("once failed: %d is not 1", *o)
+	}
+}
+
+func BenchmarkOnce(b *testing.B) {
+	const CallsPerSched = 1000
+	procs := runtime.GOMAXPROCS(-1)
+	N := int32(b.N / CallsPerSched)
+	var once Once
+	f := func() {}
+	c := make(chan bool, procs)
+	for p := 0; p < procs; p++ {
+		go func() {
+			for atomic.AddInt32(&N, -1) >= 0 {
+				runtime.Gosched()
+				for g := 0; g < CallsPerSched; g++ {
+					once.Do(f)
+				}
+			}
+			c <- true
+		}()
+	}
+	for p := 0; p < procs; p++ {
+		<-c
+	}
+}