new streams block when the max concurrent stram limit is reached.

test/end2end_test.go

@@ -806,12 +806,12 @@ func testExceedMaxStreamsLimit(t *testing.T, e env) {
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
+		defer wg.Done()
 		// The 2nd stream should block until its deadline exceeds.
 		ctx, _ := context.WithTimeout(context.Background(), time.Second)
 		if _, err := tc.StreamingInputCall(ctx); grpc.Code(err) != codes.DeadlineExceeded {
-			t.Fatalf("%v.StreamingInputCall(%v) = _, %v, want error code %d", tc, ctx, err, codes.DeadlineExceeded)
+			t.Errorf("%v.StreamingInputCall(%v) = _, %v, want error code %d", tc, ctx, err, codes.DeadlineExceeded)
 		}
-		wg.Done()
 	}()
 	wg.Wait()
 }

transport/http2_client.go

@@ -243,19 +243,20 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Strea
 		t.mu.Unlock()
 		return nil, ErrConnClosing
 	}
-	if t.streamsQuota != nil {
-		q, err := wait(ctx, t.shutdownChan, t.streamsQuota.acquire())
+	checkStreamsQuota := t.streamsQuota != nil
+	t.mu.Unlock()
+	if checkStreamsQuota {
+		sq, err := wait(ctx, t.shutdownChan, t.streamsQuota.acquire())
 		if err != nil {
-			t.mu.Unlock()
 			return nil, err
 		}
 		// Returns the quota balance back.
-		if q > 1 {
-			t.streamsQuota.add(q - 1)
+		if sq > 1 {
+			t.streamsQuota.add(sq - 1)
 		}
 	}
-	t.mu.Unlock()
 	if _, err := wait(ctx, t.shutdownChan, t.writableChan); err != nil {
+		// t.streamsQuota will be updated when t.CloseStream is invoked.
 		return nil, err
 	}
 	t.mu.Lock()