Make non-failfast RPC get new transport instead of waiting

clientconn.go

@@ -43,7 +43,6 @@ import (
 
 	"golang.org/x/net/context"
 	"golang.org/x/net/trace"
-	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/transport"
@@ -502,7 +501,11 @@ func (cc *ClientConn) getTransport(ctx context.Context, opts BalancerGetOptions)
 		}
 		return nil, nil, errConnClosing
 	}
-	t, err := ac.wait(ctx, !opts.BlockingWait)
+	// ac.wait should block on transient failure only if balancer is nil and RPC is non-failfast.
+	//  - If RPC is failfast, ac.wait should not block.
+	//  - If balancer is not nil, ac.wait should return errConnClosing on transient failure
+	//    so that non-failfast RPCs will try to get a new transport instead of waiting on ac.
+	t, err := ac.wait(ctx, cc.dopts.balancer == nil && opts.BlockingWait)
 	if err != nil {
 		if put != nil {
 			put()
@@ -754,8 +757,8 @@ func (ac *addrConn) transportMonitor() {
 }
 
 // wait blocks until i) the new transport is up or ii) ctx is done or iii) ac is closed or
-// iv) transport is in TransientFailure and the RPC is fail-fast.
-func (ac *addrConn) wait(ctx context.Context, failFast bool) (transport.ClientTransport, error) {
+// iv) transport is in TransientFailure and blocking is false.
+func (ac *addrConn) wait(ctx context.Context, blocking bool) (transport.ClientTransport, error) {
 	for {
 		ac.mu.Lock()
 		switch {
@@ -767,9 +770,9 @@ func (ac *addrConn) wait(ctx context.Context, failFast bool) (transport.ClientTr
 			ct := ac.transport
 			ac.mu.Unlock()
 			return ct, nil
-		case ac.state == TransientFailure && failFast:
+		case ac.state == TransientFailure && !blocking:
 			ac.mu.Unlock()
-			return nil, Errorf(codes.Unavailable, "grpc: RPC failed fast due to transport failure")
+			return nil, errConnClosing
 		default:
 			ready := ac.ready
 			if ready == nil {