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"
+)
+
+type dsTxnState struct {
+        sync.Mutex
+
+        toLock   []memcache.Item
+        toDelete map[string]struct{}
+}
+
+// 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 = make(map[string]struct{}, len(s.toDelete))
+}
+
+func (s *dsTxnState) Apply(sc *supportContext) {

[dnj, 2015/08/05 18:32:18]

Is there a reason these methods are exported? Maybe should be lowercase.

[iannucci, 2015/08/06 01:54:01]

Done.

+        s.Lock()
+        defer s.Unlock()
+
+        err := sc.mc.SetMulti(s.toLock)

[dnj, 2015/08/05 18:32:18]

IMO copy "toLock" while locked, but do the SetMulti outside of lock scope.

[Vadim Sh., 2015/08/06 01:23:34]

It took me a while to figure out what's going on. Document that Apply is called
from inside transaction before commit and Release right after the commit.

[iannucci, 2015/08/06 01:54:01]

That could only happen if we're ending the transaction multiple times somehow :D

[iannucci, 2015/08/06 02:37:33]

Done.

+        if err != nil {
+                sc.log.Errorf("dscache: txn.Apply SetMulti: %s", err)

[dnj, 2015/08/05 18:32:17]

Debugf?

[iannucci, 2015/08/06 01:54:01]

this ones a hard failure

+        }
+}
+
+func (s *dsTxnState) Release(sc *supportContext) {
+        s.Lock()
+        defer s.Unlock()
+
+        delKeys := make([]string, 0, len(s.toDelete))
+        for k := range s.toDelete {
+                delKeys = append(delKeys, k)
+        }
+
+        err := sc.mc.DeleteMulti(delKeys)

[dnj, 2015/08/05 18:32:18]

IMO build "delKeys" while locked, but do DelMulti outside of lock scope.

[iannucci, 2015/08/06 01:54:01]

Also can only happen if we're ending the transaction multiple times

+        if err != nil {
+                sc.log.Errorf("dscache: txn.Release DeleteMulti: %s", err)
+        }
+}
+
+func (s *dsTxnState) Add(sc *supportContext, keys []datastore.Key) {
+        lockItems, lockKeys := sc.mkAllLockItems(keys)
+        if lockItems == nil {
+                return
+        }
+
+        s.Lock()
+        defer s.Unlock()
+
+        for i, li := range lockItems {
+                k := lockKeys[i]
+                if _, ok := s.toDelete[k]; !ok {
+                        s.toLock = append(s.toLock, li)
+                        s.toDelete[k] = struct{}{}
+                }
+        }
+}