Align Group.Stats properly for 32-bit platforms.

Fixes golang/go#18334

groupcache.go

@@ -166,6 +166,8 @@ type Group struct {
  // concurrent callers.
  loadGroup flightGroup
 
+ _ int32 // force Stats to be 8-byte aligned on 32-bit platforms
+
  // Stats are statistics on the group.
  Stats Stats
 }

groupcache_test.go

@@ -27,6 +27,7 @@ import (
  "sync"
  "testing"
  "time"
+ "unsafe"
 
  "github.com/golang/protobuf/proto"
 
@@ -443,5 +444,13 @@ func TestNoDedup(t *testing.T) {
  }
 }
 
+func TestGroupStatsAlignment(t *testing.T) {
+ var g Group
+ off := unsafe.Offsetof(g.Stats)
+ if off%8 != 0 {
+ t.Fatal("Stats structure is not 8-byte aligned.")
+ }
+}
+
 // TODO(bradfitz): port the Google-internal full integration test into here,
 // using HTTP requests instead of our RPC system.