.

go/internal/xtracing/tracetest/tracetest.go

@@ -152,6 +152,7 @@ type Msg struct {
 type _chan struct {
 	t     *T
 	msgq  chan *Msg
+	down  chan struct{} // becomes ready when closed
 	_name string
 }
 
@@ -166,16 +167,21 @@ func (ch *_chan) Send(event interface{}) {
 		fmt.Printf("%s <- %T %v\n", ch.name(), event, event)
 	}
 	ack := make(chan error)
-	ch.msgq <- &Msg{event, ack}
-	err := <-ack
-	if err != nil {
-		ch.t.fatalfInNonMain("%s: send: %s", ch.name(), err)
+	select {
+	case <-ch.down:
+		ch.t.fatalfInNonMain("%s: send: channel was closed", ch.name())
+
+	case ch.msgq <- &Msg{event, ack}:
+		err := <-ack
+		if err != nil {
+			ch.t.fatalfInNonMain("%s: send: %s", ch.name(), err)
+		}
 	}
 }
 
 // Close implements ChanTx.
 func (ch *_chan) Close() {
-	close(ch.msgq)
+	close(ch.down) // note - not .msgq
 }
 
 // Recv implements ChanRx.
@@ -732,9 +738,6 @@ func (t *T) FailNow() {
 
 		default:
 		}
-
-		// in any case close channel where future Sends may arrive so that will panic too.
-		ch.Close()
 	}
 
 	// order channels by name
@@ -752,13 +755,17 @@ func (t *T) FailNow() {
 		}
 	}
 
-	// log the deadlock details and nak all senders.
+	// log the deadlock details and nak senders that we received from.
 	// nak them only after deadlock printout, so that the deadlock text
 	// comes first, and their "panics" don't get intermixed with it.
 	t.Log(bad)
 	for _, __ := range sendv {
 		__.msg.nak("XXX deadlock") // XXX reason can be custom / different
 	}
+	// in any case close channel where future Sends may arrive so that will "panic" too.
+	for _, ch := range streamTab {
+		ch.Close()
+	}
 	t.TB.FailNow()
 }