A transparent cache for datastore, backed by memcache.

filter/dscache/ds_txn_state.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 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...)
+}