common/sync/mutexpool: Add mutexpool.

common/sync/mutexpool/pool_test.go

+// 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)
+                })
+        })
+}