Reland: Refactor current GAE abstraction library to be free of the SDK*

go/src/infra/gae/libs/gae/memory/memcache.go

Index: go/src/infra/gae/libs/gae/memory/memcache.go
diff --git a/go/src/infra/gae/libs/gae/memory/memcache.go b/go/src/infra/gae/libs/gae/memory/memcache.go
new file mode 100644
index 0000000000000000000000000000000000000000..3d1ea59b7cb87b4ba8edf0aa7cd7e3acbe158ece
--- /dev/null
+++ b/go/src/infra/gae/libs/gae/memory/memcache.go
@@ -0,0 +1,228 @@
+// 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 memory
+
+import (
+	"golang.org/x/net/context"
+	"sync"
+	"time"
+
+	"infra/gae/libs/gae"
+
+	"github.com/luci/luci-go/common/clock"
+)
+
+type mcItem struct {
+	key        string
+	value      []byte
+	object     interface{}
+	flags      uint32
+	expiration time.Duration
+
+	CasID uint64
+}
+
+var _ gae.MCItem = (*mcItem)(nil)
+
+func (m *mcItem) Key() string               { return m.key }
+func (m *mcItem) Value() []byte             { return m.value }
+func (m *mcItem) Object() interface{}       { return m.object }
+func (m *mcItem) Flags() uint32             { return m.flags }
+func (m *mcItem) Expiration() time.Duration { return m.expiration }
+
+func (m *mcItem) SetKey(key string) gae.MCItem {
+	m.key = key
+	return m
+}
+func (m *mcItem) SetValue(val []byte) gae.MCItem {
+	m.value = val
+	return m
+}
+func (m *mcItem) SetObject(obj interface{}) gae.MCItem {
+	m.object = obj
+	return m
+}
+func (m *mcItem) SetFlags(flg uint32) gae.MCItem {
+	m.flags = flg
+	return m
+}
+func (m *mcItem) SetExpiration(exp time.Duration) gae.MCItem {
+	m.expiration = exp
+	return m
+}
+
+func (m *mcItem) duplicate() *mcItem {
+	ret := mcItem{}
+	ret = *m
+	ret.value = make([]byte, len(m.value))
+	copy(ret.value, m.value)
+	return &ret
+}
+
+type memcacheData struct {
+	gae.BrokenFeatures
+
+	lock  sync.Mutex
+	items map[string]*mcItem
+	casID uint64
+}
+
+// memcacheImpl binds the current connection's memcache data to an
+// implementation of {gae.Memcache, gae.Testable}.
+type memcacheImpl struct {
+	gae.Memcache
+
+	data *memcacheData
+	ctx  context.Context
+}
+
+var (
+	_ = gae.Memcache((*memcacheImpl)(nil))
+	_ = gae.Testable((*memcacheImpl)(nil))
+)
+
+// useMC adds a gae.Memcache implementation to context, accessible
+// by gae.GetMC(c)
+func useMC(c context.Context) context.Context {
+	lck := sync.Mutex{}
+	mcdMap := map[string]*memcacheData{}
+
+	return gae.SetMCFactory(c, func(ic context.Context) gae.Memcache {
+		lck.Lock()
+		defer lck.Unlock()
+
+		ns := curGID(ic).namespace
+		mcd, ok := mcdMap[ns]
+		if !ok {
+			mcd = &memcacheData{
+				BrokenFeatures: gae.BrokenFeatures{
+					DefaultError: gae.ErrMCServerError},
+				items: map[string]*mcItem{}}
+			mcdMap[ns] = mcd
+		}
+
+		return &memcacheImpl{
+			gae.DummyMC(),
+			mcd,
+			ic,
+		}
+	})
+}
+
+func (m *memcacheImpl) mkItemLocked(i gae.MCItem) (ret *mcItem) {
+	m.data.casID++
+
+	var exp time.Duration
+	if i.Expiration() != 0 {
+		exp = time.Duration(clock.Now(m.ctx).Add(i.Expiration()).UnixNano())
+	}
+	newItem := mcItem{
+		key:        i.Key(),
+		flags:      i.Flags(),
+		expiration: exp,
+		value:      i.Value(),
+		CasID:      m.data.casID,
+	}
+	return newItem.duplicate()
+}
+
+func (m *memcacheImpl) BreakFeatures(err error, features ...string) {
+	m.data.BreakFeatures(err, features...)
+}
+
+func (m *memcacheImpl) UnbreakFeatures(features ...string) {
+	m.data.UnbreakFeatures(features...)
+}
+
+func (m *memcacheImpl) NewItem(key string) gae.MCItem {
+	return &mcItem{key: key}
+}
+
+// Add implements context.MCSingleReadWriter.Add.
+func (m *memcacheImpl) Add(i gae.MCItem) error {
+	return m.data.RunIfNotBroken(func() error {
+		m.data.lock.Lock()
+		defer m.data.lock.Unlock()
+
+		if _, ok := m.retrieveLocked(i.Key()); !ok {
+			m.data.items[i.Key()] = m.mkItemLocked(i)
+			return nil
+		}
+		return gae.ErrMCNotStored
+	})
+}
+
+// CompareAndSwap implements context.MCSingleReadWriter.CompareAndSwap.
+func (m *memcacheImpl) CompareAndSwap(item gae.MCItem) error {
+	return m.data.RunIfNotBroken(func() error {
+		m.data.lock.Lock()
+		defer m.data.lock.Unlock()
+
+		if cur, ok := m.retrieveLocked(item.Key()); ok {
+			casid := uint64(0)
+			if mi, ok := item.(*mcItem); ok && mi != nil {
+				casid = mi.CasID
+			}
+
+			if cur.CasID == casid {
+				m.data.items[item.Key()] = m.mkItemLocked(item)
+			} else {
+				return gae.ErrMCCASConflict
+			}
+		} else {
+			return gae.ErrMCNotStored
+		}
+		return nil
+	})
+}
+
+// Set implements context.MCSingleReadWriter.Set.
+func (m *memcacheImpl) Set(i gae.MCItem) error {
+	return m.data.RunIfNotBroken(func() error {
+		m.data.lock.Lock()
+		defer m.data.lock.Unlock()
+		m.data.items[i.Key()] = m.mkItemLocked(i)
+		return nil
+	})
+}
+
+// Get implements context.MCSingleReadWriter.Get.
+func (m *memcacheImpl) Get(key string) (itm gae.MCItem, err error) {
+	err = m.data.RunIfNotBroken(func() (err error) {
+		m.data.lock.Lock()
+		defer m.data.lock.Unlock()
+		if val, ok := m.retrieveLocked(key); ok {
+			itm = val.duplicate().SetExpiration(0)
+		} else {
+			err = gae.ErrMCCacheMiss
+		}
+		return
+	})
+	return
+}
+
+// Delete implements context.MCSingleReadWriter.Delete.
+func (m *memcacheImpl) Delete(key string) error {
+	return m.data.RunIfNotBroken(func() error {
+		m.data.lock.Lock()
+		defer m.data.lock.Unlock()
+
+		if _, ok := m.retrieveLocked(key); ok {
+			delete(m.data.items, key)
+			return nil
+		}
+		return gae.ErrMCCacheMiss
+	})
+}
+
+func (m *memcacheImpl) retrieveLocked(key string) (*mcItem, bool) {
+	ret, ok := m.data.items[key]
+	if ok && ret.Expiration() != 0 && ret.Expiration() < time.Duration(clock.Now(m.ctx).UnixNano()) {
+		ret = nil
+		ok = false
+		delete(m.data.items, key)
+	}
+	return ret, ok
+}