8253940: com/sun/jdi/JdwpAttachTest.java failed with "RuntimeException: ERROR: LingeredApp.startApp was able to attach"

Reviewed-by: cjplummer, lmesnik

Author: Alex Menkov

test/jdk/com/sun/jdi/JdwpAttachTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2021, 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
@@ -50,10 +50,13 @@
 public class JdwpAttachTest {
 
     // Set to true to perform testing of attach from wrong address (expected to fail).
-    // It's off by default as it caused significant test time increase\
+    // It's off by default as it caused significant test time increase
     // (tests <number_of_addresses> * <number_of_addresses> cases, each case fails by timeout).
     private static boolean testFailedAttach = false;
 
+    // A flag to exclude testcases which can cause intermittent CI failures.
+    private static boolean testPotentiallyUnstableCases = false;
+
     public static void main(String[] args) throws Exception {
         List<InetAddress> addresses = Utils.getAddressesWithSymbolicAndNumericScopes();
 
@@ -81,11 +84,15 @@ public static void main(String[] args) throws Exception {
             }
         }
 
-        // by using "localhost" or empty hostname
-        // we should be able to attach to both IPv4 and IPv6 addresses (127.0.0.1 & ::1)
+        // By using "localhost" or empty hostname we should be able to attach
+        // to both IPv4 and IPv6 addresses (127.0.0.1 & ::1).
+        // By default test verifies only "preferred" family (IPv4 or IPv6).
+        // Need to set testPotentiallyUnstableCases to true to perform full testing.
         InetAddress localAddresses[] = InetAddress.getAllByName("localhost");
         for (int i = 0; i < localAddresses.length; i++) {
-            attachTest(localAddresses[i].getHostAddress(), "", true);
+            if (testPotentiallyUnstableCases || addressIsSafeToConnectToLocalhost(localAddresses[i])) {
+                attachTest(localAddresses[i].getHostAddress(), "", true);
+            }
         }
     }
 
@@ -168,6 +175,15 @@ private static void setConnectorArg(Map<String, Connector.Argument> args, String
         arg.setValue(value);
     }
 
+    // Attach to localhost tries to connect to both IPv4 and IPv6 loopback addresses.
+    // But sometimes it causes interference with other processes which can listen
+    // on the same port but different loopback address.
+    // The method checks if the address is safe to test with current network config.
+    private static boolean addressIsSafeToConnectToLocalhost(InetAddress addr) {
+        boolean ipv6 = Boolean.parseBoolean(System.getProperty("java.net.preferIPv6Addresses"));
+        return ipv6 == (addr instanceof Inet6Address);
+    }
+
     private static long startTime = System.currentTimeMillis();
 
     private static void log(Object o) {