compactor: Fix data race in revision compactor test

Use atomic functions to manipulate `rev` of `fakeRevGetter`
so that the tester goroutine can update the
value without race with the compactor's goroutine.

compactor/compactor_test.go

@@ -15,6 +15,8 @@
 package compactor
 
 import (
+	"sync/atomic"
+
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
 	"github.com/coreos/etcd/pkg/testutil"
 	"golang.org/x/net/context"
@@ -36,6 +38,10 @@ type fakeRevGetter struct {
 
 func (fr *fakeRevGetter) Rev() int64 {
 	fr.Record(testutil.Action{Name: "g"})
-	fr.rev++
+	rev := atomic.AddInt64(&fr.rev, 1)
-	return fr.rev
+	return rev
+}
+
+func (fr *fakeRevGetter) SetRev(rev int64) {
+	atomic.StoreInt64(&fr.rev, rev)
 }

compactor/revision_test.go

@@ -42,7 +42,7 @@ func TestRevision(t *testing.T) {
 	rg.Wait(1)
 	// nothing happens
 
-	rg.rev = 99 // will be 100
+	rg.SetRev(99) // will be 100
 	expectedRevision := int64(90)
 	fc.Advance(checkCompactionInterval)
 	rg.Wait(1)
@@ -55,12 +55,12 @@ func TestRevision(t *testing.T) {
 	}
 
 	// skip the same revision
-	rg.rev = 99 // will be 100
+	rg.SetRev(99) // will be 100
 	expectedRevision = int64(90)
 	rg.Wait(1)
 	// nothing happens
 
-	rg.rev = 199 // will be 200
+	rg.SetRev(199) // will be 200
 	expectedRevision = int64(190)
 	fc.Advance(checkCompactionInterval)
 	rg.Wait(1)