concurrency: retry snapshot serializable stm if writes since first header rev

clientv3/concurrency/example_stm_test.go

@@ -58,7 +58,7 @@ func ExampleSTM_apply() {
 
 		// transfer amount
 		xfer := fromInt / 2
-		fromInt, toInt = fromInt-xfer, toInt-xfer
+		fromInt, toInt = fromInt-xfer, toInt+xfer
 
 		// writeback
 		stm.Put(fromK, fmt.Sprintf("%d", fromInt))

clientv3/concurrency/stm.go

@@ -193,11 +193,12 @@ func (rs readSet) add(keys []string, txnresp *v3.TxnResponse) {
 	}
 }
 
+// first returns the store revision from the first fetch
 func (rs readSet) first() int64 {
 	ret := int64(math.MaxInt64 - 1)
 	for _, resp := range rs {
-		if len(resp.Kvs) > 0 && resp.Kvs[0].ModRevision < ret {
-			ret = resp.Kvs[0].ModRevision
+		if rev := resp.Header.Revision; rev < ret {
+			ret = rev
 		}
 	}
 	return ret

integration/v3_stm_test.go

@@ -15,14 +15,15 @@
 package integration
 
 import (
+	"context"
 	"fmt"
 	"math/rand"
 	"strconv"
 	"testing"
 
 	v3 "github.com/coreos/etcd/clientv3"
 	"github.com/coreos/etcd/clientv3/concurrency"
-	"golang.org/x/net/context"
+	"github.com/coreos/etcd/pkg/testutil"
 )
 
 // TestSTMConflict tests that conflicts are retried.
@@ -253,3 +254,36 @@ func TestSTMApplyOnConcurrentDeletion(t *testing.T) {
 		t.Fatalf("bad value. got %+v, expected 'bar2' value", resp)
 	}
 }
+
+func TestSTMSerializableSnapshotPut(t *testing.T) {
+	clus := NewClusterV3(t, &ClusterConfig{Size: 1})
+	defer clus.Terminate(t)
+
+	cli := clus.Client(0)
+	// key with lower create/mod revision than keys being updated
+	_, err := cli.Put(context.TODO(), "a", "0")
+	testutil.AssertNil(t, err)
+
+	tries := 0
+	applyf := func(stm concurrency.STM) error {
+		if tries > 2 {
+			return fmt.Errorf("too many retries")
+		}
+		tries++
+		stm.Get("a")
+		stm.Put("b", "1")
+		return nil
+	}
+
+	iso := concurrency.WithIsolation(concurrency.SerializableSnapshot)
+	_, err = concurrency.NewSTM(cli, applyf, iso)
+	testutil.AssertNil(t, err)
+	_, err = concurrency.NewSTM(cli, applyf, iso)
+	testutil.AssertNil(t, err)
+
+	resp, err := cli.Get(context.TODO(), "b")
+	testutil.AssertNil(t, err)
+	if resp.Kvs[0].Version != 2 {
+		t.Fatalf("bad version. got %+v, expected version 2", resp)
+	}
+}