8269657: Test java/nio/channels/DatagramChannel/Loopback.java failed:…

… Unexpected message

Backport-of: c798316bc4cb33fd902f926030d8a0b6870d661a

test/jdk/java/nio/channels/DatagramChannel/Loopback.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -118,7 +118,8 @@ static void test(ProtocolFamily family, InetAddress group, NetworkInterface ni)
 
             // send datagram to multicast group
             System.out.format("send %s -> %s%n", dc.getLocalAddress(), target);
-            ByteBuffer src = ByteBuffer.wrap("hello".getBytes("UTF-8"));
+            String str = "hello " + System.nanoTime();
+            ByteBuffer src = ByteBuffer.wrap(str.getBytes("UTF-8"));
             dc.send(src, target);
 
             // receive datagram sent to multicast group
@@ -142,6 +143,7 @@ static void test(ProtocolFamily family, InetAddress group, NetworkInterface ni)
             System.out.format("send %s -> %s%n", dc.getLocalAddress(), target);
             src.clear();
             dc.send(src, target);
+            src.flip();
 
             // test that we don't receive the datagram sent to multicast group
             dc.configureBlocking(false);
@@ -157,10 +159,16 @@ static void test(ProtocolFamily family, InetAddress group, NetworkInterface ni)
                     } else {
                         sel.selectedKeys().clear();
                         SocketAddress sender = dc.receive(dst);
+                        if (src.mismatch(dst) != -1) {
+                            System.out.println("src: " + src + "not equal to dst: " + dst);
+                            dst.clear();
+                            continue;
+                        }
                         if (sender != null) {
                             System.out.format("received %s from %s%n", dst, sender);
                             senderPort = ((InetSocketAddress) sender).getPort();
-                            assertTrue(senderPort != localPort, "Unexpected message");
+                            assertTrue(senderPort != localPort,
+                                    "Unexpected message: localPort=" + localPort);
                         }
                     }
                 }