A simple memcache lock for appengine.

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

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