A simple memcache lock for appengine.

go/src/infra/gae/libs/memlock/memlock_test.go

Index: go/src/infra/gae/libs/memlock/memlock_test.go
diff --git a/go/src/infra/gae/libs/memlock/memlock_test.go b/go/src/infra/gae/libs/memlock/memlock_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..891d61991afd36dd4d62a6748f75d3fa5703c05f
--- /dev/null
+++ b/go/src/infra/gae/libs/memlock/memlock_test.go
@@ -0,0 +1,102 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// +build appengine
+
+package memlock
+
+import (
+	"testing"
+	"time"
+
+	"appengine/memcache"
+
+	"infra/gae/libs/context/memory"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func init() {
+	delay = time.Millisecond
+	memcacheLockTime = time.Millisecond * 4
+}
+
+func TestSimple(t *testing.T) {
+
+	Convey("basic locking", t, func() {
+		c := memory.NewBestContext()
+		mc := c.Memcache
+		mcImpl := mc.(*memory.MemcacheImpl)
+
+		l, err := New(mc, "testkey", "")
+		So(err, ShouldBeNil)
+
+		Convey("fails to acquire when memcache is down", func() {
+			mcImpl.SetBrokenFeatures("Add")
+			gotIt := l.TryWithLock(func(check func() bool) {
+				// should never reach here
+				So(false, ShouldBeTrue)
+			})
+			So(gotIt, ShouldBeFalse)
+		})
+
+		Convey("can acquire when empty", func() {
+			gotIt := l.TryWithLock(func(check func() bool) {
+				So(check(), ShouldBeTrue)
+
+				Convey("waiting for a while keeps refreshing the lock", func() {
+					time.Sleep(memcacheLockTime * 8)
+					So(check(), ShouldBeTrue)
+				})
+
+				Convey("but sometimes we might lose it", func() {
+					Convey("because it was evicted", func() {
+						mc.Delete("memlock:testkey")
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+
+					Convey("because it got evicted (but we race)", func() {
+						mc.Set(&memcache.Item{
+							Key:   "memlock:testkey",
+							Value: []byte(""),
+						})
+					})
+
+					Convey("or because it was stolen", func() {
+						mc.Set(&memcache.Item{
+							Key:   "memlock:testkey",
+							Value: []byte("wat"),
+						})
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+
+					Convey("or because of service issues", func() {
+						mcImpl.SetBrokenFeatures("CompareAndSwap")
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+				})
+			})
+			So(gotIt, ShouldBeTrue)
+
+			Convey("but reentry is a no-no", func() {
+				gotIt := l.TryWithLock(func(check func() bool) {
+					So(check(), ShouldBeTrue)
+					So(func() {
+						l.TryWithLock(func(func() bool) {})
+					}, ShouldPanic)
+				})
+				So(gotIt, ShouldBeTrue)
+			})
+		})
+
+		Convey("an empty context id is random", func() {
+			l2, err := New(mc, "testkey", "")
+			So(err, ShouldBeNil)
+			So(l2.clientID, ShouldNotResemble, l.clientID)
+		})
+	})
+}