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..49b892b763715e3036b4af2baa50b1d66c8563df
--- /dev/null
+++ b/go/src/infra/gae/libs/memlock/memlock_test.go
@@ -0,0 +1,100 @@
+// 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.
+
+package memlock
+
+import (
+	"fmt"
+	"infra/gae/libs/wrapper"
+	"infra/gae/libs/wrapper/memory"
+	"testing"
+	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
+	"golang.org/x/net/context"
+
+	"appengine/memcache"
+)
+
+func init() {
+	delay = time.Millisecond
+	memcacheLockTime = time.Millisecond * 4
+}
+
+func TestSimple(t *testing.T) {
+	// TODO(riannucci): Mock time.After so that we don't have to delay for real.
+
+	Convey("basic locking", t, func() {
+		c := memory.Use(context.Background())
+		mc := wrapper.GetMC(c).(interface {
+			wrapper.Testable
+			wrapper.MCSingleReadWriter
+		})
+
+		Convey("fails to acquire when memcache is down", func() {
+			mc.BreakFeatures(nil, "Add")
+			err := TryWithLock(c, "testkey", "id", func(check func() bool) error {
+				// should never reach here
+				So(false, ShouldBeTrue)
+				return nil
+			})
+			So(err, ShouldEqual, ErrFailedToLock)
+		})
+
+		Convey("returns the inner error", func() {
+			toRet := fmt.Errorf("sup")
+			err := TryWithLock(c, "testkey", "id", func(check func() bool) error {
+				return toRet
+			})
+			So(err, ShouldEqual, toRet)
+		})
+
+		Convey("can acquire when empty", func() {
+			err := TryWithLock(c, "testkey", "id", func(check func() bool) error {
+				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(memlockKeyPrefix + "testkey")
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+
+					Convey("because it got evicted (but we race)", func() {
+						mc.Set(&memcache.Item{
+							Key:   memlockKeyPrefix + "testkey",
+							Value: []byte(""),
+						})
+					})
+
+					Convey("or because it was stolen", func() {
+						mc.Set(&memcache.Item{
+							Key:   memlockKeyPrefix + "testkey",
+							Value: []byte("wat"),
+						})
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+
+					Convey("or because of service issues", func() {
+						mc.BreakFeatures(nil, "CompareAndSwap")
+						time.Sleep(memcacheLockTime)
+						So(check(), ShouldBeFalse)
+					})
+				})
+				return nil
+			})
+			So(err, ShouldBeNil)
+		})
+
+		Convey("an empty context id is an error", func() {
+			So(TryWithLock(c, "testkey", "", nil), ShouldEqual, ErrEmptyClientID)
+		})
+	})
+}