A transparent cache for datastore, backed by memcache.

filter/dscache/ds_txn_state.go

Index: filter/dscache/ds_txn_state.go
diff --git a/filter/dscache/ds_txn_state.go b/filter/dscache/ds_txn_state.go
new file mode 100644
index 0000000000000000000000000000000000000000..88345f82f7c16851a0b25654b6a6c012014eb532
--- /dev/null
+++ b/filter/dscache/ds_txn_state.go
@@ -0,0 +1,65 @@
+// 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 dscache
+
+import (
+	"sync"
+
+	"github.com/luci/gae/service/datastore"
+	"github.com/luci/gae/service/memcache"
+	"github.com/luci/luci-go/common/logging"
+)
+
+type dsTxnState struct {
+	sync.Mutex
+
+	toLock   []memcache.Item
+	toDelete []string
+}
+
+// Reset sets the transaction state back to its 0 state. This is used so that
+// when a transaction retries the function, we don't accidentally leak state
+// from one function to the next.
+func (s *dsTxnState) Reset() {
+	s.Lock()
+	defer s.Unlock()
+	// reduce capacity back to 0, but keep the allocated array. If the transaction
+	// body retries, it'll probably end up re-allocating the same amount of space
+	// anyway.
+	s.toLock = s.toLock[:0]
+	s.toDelete = s.toDelete[:0]
+}
+
+func (s *dsTxnState) Apply(mc memcache.Interface, log logging.Logger) {
+	s.Lock()
+	defer s.Unlock()
+
+	err := mc.SetMulti(s.toLock)
+	if err != nil {
+		log.Errorf("dscache: txn.Apply SetMulti: %s", err)
+	}
+}
+
+func (s *dsTxnState) Release(mc memcache.Interface, log logging.Logger) {
+	s.Lock()
+	defer s.Unlock()
+
+	err := mc.DeleteMulti(s.toDelete)
+	if err != nil {
+		log.Errorf("dscache: txn.Release DeleteMulti: %s", err)
+	}
+}
+
+func (s *dsTxnState) Add(mc memcache.Interface, keys []datastore.Key) {
+	lockItems, lockKeys := mkAllLockItems(mc, keys)
+	if lockItems == nil {
+		return
+	}
+
+	s.Lock()
+	defer s.Unlock()
+	s.toLock = append(s.toLock, lockItems...)
+	s.toDelete = append(s.toDelete, lockKeys...)
+}