Merge pull request #7816 from heyitsanthony/v3client-blankctx

v3client: wrap watch ctxs with blank ctx

etcdserver/api/v3client/v3client.go

@@ -15,13 +15,14 @@
 package v3client
 
 import (
-	"context"
 	"time"
 
 	"github.com/coreos/etcd/clientv3"
 	"github.com/coreos/etcd/etcdserver"
 	"github.com/coreos/etcd/etcdserver/api/v3rpc"
 	"github.com/coreos/etcd/proxy/grpcproxy/adapter"
+
+	"golang.org/x/net/context"
 )
 
 // New creates a clientv3 client that wraps an in-process EtcdServer. Instead
@@ -37,7 +38,7 @@ func New(s *etcdserver.EtcdServer) *clientv3.Client {
 	c.Lease = clientv3.NewLeaseFromLeaseClient(lc, time.Second)
 
 	wc := adapter.WatchServerToWatchClient(v3rpc.NewWatchServer(s))
-	c.Watcher = clientv3.NewWatchFromWatchClient(wc)
+	c.Watcher = &watchWrapper{clientv3.NewWatchFromWatchClient(wc)}
 
 	mc := adapter.MaintenanceServerToMaintenanceClient(v3rpc.NewMaintenanceServer(s))
 	c.Maintenance = clientv3.NewMaintenanceFromMaintenanceClient(mc)
@@ -49,3 +50,18 @@ func New(s *etcdserver.EtcdServer) *clientv3.Client {
 
 	return c
 }
+
+// BlankContext implements Stringer on a context so the ctx string doesn't
+// depend on the context's WithValue data, which tends to be unsynchronized
+// (e.g., x/net/trace), causing ctx.String() to throw data races.
+type blankContext struct{ context.Context }
+
+func (*blankContext) String() string { return "(blankCtx)" }
+
+// watchWrapper wraps clientv3 watch calls to blank out the context
+// to avoid races on trace data.
+type watchWrapper struct{ clientv3.Watcher }
+
+func (ww *watchWrapper) Watch(ctx context.Context, key string, opts ...clientv3.OpOption) clientv3.WatchChan {
+	return ww.Watcher.Watch(&blankContext{ctx}, key, opts...)
+}