JDK 9 RFR of JDK-8132548: java/lang/ThreadGroup/Stop.java fails with "RuntimeException: Failure"

[David Holmes]

Hi Amy,

Thanks for tackling this.

On 8/07/2016 4:01 PM, Amy Lu wrote:
> Thank you Joe for your review.
>
> The intent is to give it more chance "for the thread group stop to be
> issued", not to extend the whole test execution timeout.
>
> I updated the webrev to make this in a retry, limit to 5 times of retry:
> http://cr.openjdk.java.net/~amlu/8132548/webrev.01/

The retry serves no purpose here. groupStopped is being set to true and 
the waiting thread has been notified, so the loop will terminate after 
the first sleep. The failure happens when the main thread checks the 
isAlive() status of the second thread before the ThreadGroup.stop has 
actually had a chance to stop and terminate it - such that isAlive is 
now false. That is why I suggested waiting a bit longer by extending the 
sleep.

I agree that making the test last at least 5 seconds is not ideal, but I 
didn't think it would be an issue in the big picture of testing.

Ideally explicit "synchronization" is better than sleeps but that would 
again be missing the point with this test. We expect the thread to 
terminate, if it hasn't terminated in a "reasonable" time we consider 
the stop() to have failed and the test to fail. To that end we could 
remove the sleep altogether and change:

boolean failed = second.isAlive();

to

try {
   second.join(1000);
} catch (InterruptedException shouldNotHappen) {}
boolean failed = second.isAlive();

Now we use explicit event synchronization - great! But the test has the 
same failure issue now as it did with the sleep. Putting in a 
CountDownLatch would have exactly the same problem: we expect the second 
thread to signal the latch as it terminates, but if that doesn't happen 
within a "reasonable" amount of time, then we deem the stop() to have 
failed and the test to have failed.

Also note that the more code we add the more likely the second call to 
second.stop() triggers an async exception in code that can't handle it 
and results in an even worse failure mode!

The only thing I can suggest is to get rid of the explicit sleep (or 
join, or latch.await() etc) and simply recode as an infinite loop and 
rely on the test harness to tear things down when the overall test 
timeout kicks in. That way the test either passes or is timed-out, there 
is no explicit failure - but a busy loop is also bad so you would want a 
small sleep in there anyway:

while (second.isAlive()) {
   Thread.sleep(10);
}
// Test passed - if we never get here the test times out and
// we implicitly fail.

Thanks,
David

> Thanks,
> Amy
>
> On 7/8/16 12:15 PM, joe darcy wrote:
>> Hi Amy,
>>
>> I'm a bit uncomfortable with the fix as-is.
>>
>> Rather than hard-coding sleep values, if sleep values are needed I
>> think it is a better practice to use ones that are scaled with the
>> jtreg timeout factors, etc. used to run the tests. Please instead use
>> something like the adjustTimeout method of
>>
>>     $JDK_FOREST_ROOT/test/lib/share/classes/jdk/test/lib/Utils
>>
>> As a general comment, I'd prefer we don't just up timeout values for
>> tests. That can cause the whole test suite run to slow down, which is
>> undesirable especially if the condition in question may actually be
>> satisfied in many cases much faster than the timeout value.
>>
>> Thanks,
>>
>> -Joe
>>
>>
>> On 7/7/2016 7:01 PM, Amy Lu wrote:
>>> Please review this trivial fix for test:java/lang/ThreadGroup/Stop.java
>>>
>>> Though this is a test for a deprecated API, failed with very very low
>>> frequency and hard to reproduce (I got no luck to reproduce it), I’d
>>> like to patch it as suggested: extend the sleep in the main thread
>>> from one second to five seconds. Also added 'volatile' to the boolean
>>> variable 'groupStopped'.
>>>
>>> bug: https://bugs.openjdk.java.net/browse/JDK-8132548
>>> webrev: http://cr.openjdk.java.net/~amlu/8132548/webrev.00/
>>>
>>> Thanks,
>>> Amy
>>>
>>>
>>> --- old/test/java/lang/ThreadGroup/Stop.java    2016-07-04
>>> 14:53:59.000000000 +0800
>>> +++ new/test/java/lang/ThreadGroup/Stop.java    2016-07-04
>>> 14:53:58.000000000 +0800
>>> @@ -1,5 +1,5 @@
>>>  /*
>>> - * Copyright (c) 1999, 2011, Oracle and/or its affiliates. All
>>> rights reserved.
>>> + * Copyright (c) 1999, 2016, 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
>>> @@ -29,7 +29,7 @@
>>>   */
>>>
>>>  public class Stop implements Runnable {
>>> -    private static boolean groupStopped = false ;
>>> +    private static volatile boolean groupStopped = false ;
>>>      private static final Object lock = new Object();
>>>
>>>      private static final ThreadGroup group = new ThreadGroup("");
>>> @@ -70,7 +70,7 @@
>>>              while (!groupStopped) {
>>>                  lock.wait();
>>>                  // Give the other thread a chance to stop
>>> -                Thread.sleep(1000);
>>> +                Thread.sleep(5000);
>>>              }
>>>          }
>>>
>>>
>>>
>>
>