Interface update, per-method Contexts.

impl/memory/datastore_data.go

Index: impl/memory/datastore_data.go
diff --git a/impl/memory/datastore_data.go b/impl/memory/datastore_data.go
index 95d66fb831b7b65dab1d944b8b976ae2f0e58e1c..6d995b8949ecc5062d9851c31447d0c480106907 100644
--- a/impl/memory/datastore_data.go
+++ b/impl/memory/datastore_data.go
@@ -9,11 +9,11 @@ import (
 	"fmt"
 	"strings"
 	"sync"
-	"sync/atomic"
 
 	ds "github.com/luci/gae/service/datastore"
 	"github.com/luci/gae/service/datastore/serialize"
 	"github.com/luci/luci-go/common/errors"
+
 	"golang.org/x/net/context"
 )
 
@@ -176,15 +176,15 @@ func (d *dataStoreData) namespaces() []string {
 /////////////////////////// indexes(dataStoreData) ////////////////////////////
 
 func groupMetaKey(key *ds.Key) []byte {
-	return keyBytes(ds.NewKey("", "", "__entity_group__", "", 1, key.Root()))
+	return keyBytes(ds.KeyContext{}.NewKey("__entity_group__", "", 1, key.Root()))
 }
 
 func groupIDsKey(key *ds.Key) []byte {
-	return keyBytes(ds.NewKey("", "", "__entity_group_ids__", "", 1, key.Root()))
+	return keyBytes(ds.KeyContext{}.NewKey("__entity_group_ids__", "", 1, key.Root()))
 }
 
 func rootIDsKey(kind string) []byte {
-	return keyBytes(ds.NewKey("", "", "__entity_root_ids__", kind, 0, nil))
+	return keyBytes(ds.KeyContext{}.NewKey("__entity_root_ids__", kind, 0, nil))
 }
 
 func curVersion(ents memCollection, key []byte) int64 {
@@ -279,7 +279,7 @@ func (d *dataStoreData) fixKeyLocked(ents memCollection, key *ds.Key) (*ds.Key,
 		if err != nil {
 			return key, err
 		}
-		key = ds.NewKey(key.AppID(), key.Namespace(), key.Kind(), "", id, key.Parent())
+		key = key.KeyContext().NewKey(key.Kind(), "", id, key.Parent())
 	}
 	return key, nil
 }
@@ -412,7 +412,7 @@ func (d *dataStoreData) canApplyTxn(obj memContextObj) bool {
 		if len(muts) == 0 { // read-only
 			continue
 		}
-		prop, err := serialize.ReadProperty(bytes.NewBufferString(rk), serialize.WithContext, "", "")
+		prop, err := serialize.ReadProperty(bytes.NewBufferString(rk), serialize.WithContext, ds.KeyContext{})
 		memoryCorruption(err)
 
 		k := prop.Value().(*ds.Key)
@@ -455,9 +455,11 @@ func (d *dataStoreData) mkTxn(o *ds.TransactionOptions) memContextObj {
 		// alias to the main datastore's so that testing code can have primitive
 		// access to break features inside of transactions.
 		parent: d,
-		isXG:   o != nil && o.XG,
-		snap:   d.head.Snapshot(),
-		muts:   map[string][]txnMutation{},
+		txn: &transactionImpl{
+			isXG: o != nil && o.XG,
+		},
+		snap: d.head.Snapshot(),
+		muts: map[string][]txnMutation{},
 	}
 }
 
@@ -475,9 +477,7 @@ type txnDataStoreData struct {
 
 	parent *dataStoreData
 
-	// boolean 0 or 1, use atomic.*Int32 to access.
-	closed int32
-	isXG   bool
+	txn *transactionImpl
 
 	snap memStore
 
@@ -492,11 +492,11 @@ var _ memContextObj = (*txnDataStoreData)(nil)
 const xgEGLimit = 25
 
 func (*txnDataStoreData) canApplyTxn(memContextObj) bool { return false }
+
 func (td *txnDataStoreData) endTxn() {
-	if atomic.LoadInt32(&td.closed) == 1 {
-		panic("cannot end transaction twice")
+	if err := td.txn.close(); err != nil {
+		panic(err)
 	}
-	atomic.StoreInt32(&td.closed, 1)
 }
 func (*txnDataStoreData) applyTxn(context.Context, memContextObj) {
 	impossible(fmt.Errorf("cannot create a recursive transaction"))
@@ -509,8 +509,8 @@ func (*txnDataStoreData) mkTxn(*ds.TransactionOptions) memContextObj {
 func (td *txnDataStoreData) run(f func() error) error {
 	// Slightly different from the SDK... datastore and taskqueue each implement
 	// this here, where in the SDK only datastore.transaction.Call does.
-	if atomic.LoadInt32(&td.closed) == 1 {
-		return errors.New("datastore: transaction context has expired")
+	if err := td.txn.valid(); err != nil {
+		return err
 	}
 	return f()
 }
@@ -534,12 +534,12 @@ func (td *txnDataStoreData) writeMutation(getOnly bool, key *ds.Key, data ds.Pro
 
 	if _, ok := td.muts[rk]; !ok {
 		limit := 1
-		if td.isXG {
+		if td.txn.isXG {
 			limit = xgEGLimit
 		}
 		if len(td.muts)+1 > limit {
 			msg := "cross-group transaction need to be explicitly specified (xg=True)"
-			if td.isXG {
+			if td.txn.isXG {
 				msg = "operating on too many entity groups in a single transaction"
 			}
 			return errors.New(msg)
@@ -603,7 +603,7 @@ func keyBytes(key *ds.Key) []byte {
 
 func rpm(data []byte) (ds.PropertyMap, error) {
 	return serialize.ReadPropertyMap(bytes.NewBuffer(data),
-		serialize.WithContext, "", "")
+		serialize.WithContext, ds.KeyContext{})
 }
 
 func namespaces(store memStore) []string {