Interface update, per-method Contexts.

impl/memory/transaction.go

+// Copyright 2015 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package memory
+
+import (
+        "sync/atomic"
+
+        ds "github.com/luci/gae/service/datastore"
+
+        "github.com/luci/luci-go/common/errors"
+
+        "golang.org/x/net/context"
+)
+
+type transactionImpl struct {
+        // boolean 0 or 1, use atomic.*Int32 to access.
+        closed int32
+        isXG   bool
+}
+
+func (ti *transactionImpl) close() error {
+        if !atomic.CompareAndSwapInt32(&ti.closed, 0, 1) {
+                return errors.New("transaction is already closed")
+        }
+        return nil
+}
+
+func (ti *transactionImpl) valid() error {
+        if atomic.LoadInt32(&ti.closed) == 1 {
+                return errors.New("transaction has expired")
+        }
+        return nil
+}
+
+func assertTxnValid(c context.Context) error {
+        t := ds.CurrentTransaction(c)
+        if t == nil {
+                return nil
+        }
+
+        return t.(*transactionImpl).valid()
+}