common/sync/mutexpool: Add mutexpool.

common/sync/mutexpool/pool_test.go

Index: common/sync/mutexpool/pool_test.go
diff --git a/common/sync/mutexpool/pool_test.go b/common/sync/mutexpool/pool_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..8b3a638e5a2031b40505da9ce0d5940367dc3138
--- /dev/null
+++ b/common/sync/mutexpool/pool_test.go
@@ -0,0 +1,55 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package mutexpool
+
+import (
+	"sync"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestPool(t *testing.T) {
+	t.Parallel()
+
+	Convey(`A mutex pool`, t, func() {
+		var pool P
+
+		Convey(`Can handle multiple concurrent Mutex accesses, and will clean up when finished.`, func() {
+			const total = 1000
+			var value int
+			var wg sync.WaitGroup
+
+			wg.Add(total)
+			for i := 0; i < total; i++ {
+				go func() {
+					pool.WithMutex("foo", func() {
+						value++
+					})
+					wg.Done()
+				}()
+			}
+
+			wg.Wait()
+			So(value, ShouldEqual, total)
+			So(pool.mutexes, ShouldHaveLength, 0)
+		})
+
+		Convey(`Can handle multiple keys.`, func() {
+			const total = 100
+			var recLock func(int)
+			recLock = func(v int) {
+				if v < total {
+					pool.WithMutex(v, func() {
+						So(pool.mutexes, ShouldHaveLength, v+1)
+						recLock(v + 1)
+					})
+				}
+			}
+			recLock(0)
+			So(pool.mutexes, ShouldHaveLength, 0)
+		})
+	})
+}