On 12/23/2013 2:02 PM, srikalyan chandrashekar wrote:
Hi Mandy, after some trials i could simulate the failure again (now with UEH in place), however the UEH now cannot print enough details as it also tries to allocate memory, when it does Thread.getName()(it internally creates a String object), printStackTrace() also creates new WrappedPrintStream object. See the following trace

That's what I later also thought that may run into after suggesting UEH and no object can be allocated at this point.

It worths trying Peter's suggestion to override the modified version of Reference class with instrumentation and see what you will get.


Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "Reference Handler"
ERROR: java.lang.Exception: Reference Handler thread died.
        at OOMEInReferenceHandler.main(OOMEInReferenceHandler.java:105)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:483)
at com.sun.javatest.regtest.MainWrapper$MainThread.run(MainWrapper.java:94)
        at java.lang.Thread.run(Thread.java:744)

Meanwhile i am trying looking around to actually print something useful without allocating any new memory.


On 12/20/2013 01:00 PM, srikalyan wrote:
Hi Mandy, yes I ran with JTreg to simulate the failure, i will try the UEH patch to see if it sheds some light and get back to you. Thanks for the direction :)

Ph: (408)-585-8040

On 12/19/13, 8:33 PM, Mandy Chung wrote:
Hi Srikalyan,

Maybe you can get add an uncaught handler to see if you can get
any information.  I ran it for 1000 times but not able to duplicate
the failure.  Did you run it with jtreg (I didn't)?

Below is the patch to install a thread's uncaught handler that
you can take and try.

diff --git a/test/java/lang/ref/OOMEInReferenceHandler.java b/test/java/lang/ref/OOMEInReferenceHand
--- a/test/java/lang/ref/OOMEInReferenceHandler.java
+++ b/test/java/lang/ref/OOMEInReferenceHandler.java
@@ -51,6 +51,14 @@
          return first;

+     static class UEH implements Thread.UncaughtExceptionHandler {
+         public void uncaughtException(Thread t, Throwable e) {
+ System.err.println("ERROR: " + t.getName() + " exception " +
+                 e.getMessage());
+             e.printStackTrace();
+         }
+     }
      public static void main(String[] args) throws Exception {
// preinitialize the InterruptedException class so that the reference handler // does not die due to OOME when loading the class if it is the first use
@@ -77,6 +85,8 @@
throw new IllegalStateException("Couldn't find Reference Handler thread.");

+ referenceHandlerThread.setUncaughtExceptionHandler(new UEH());
          ReferenceQueue<Object> refQueue = new ReferenceQueue<>();
          Object referent = new Object();
WeakReference<Object> weakRef = new WeakReference<>(referent, refQueue);

On 12/19/2013 6:57 PM, srikalyan chandrashekar wrote:
Hi David Thanks for your comments, the unguarded part(clean and enqueue) in the Reference Handler thread does not seem to create any new objects, so it is the application(the test in this case) which is adding objects to heap and causing the Reference Handler to die with OOME. I am still unsure about the side effects of the code change and agree with your thoughts(on memory exhaustion test's reliability).

PS: hotspot dev alias removed from CC.


On 12/19/13 5:08 PM, David Holmes wrote:
Hi Kalyan,

This is not a hotspot issue so I'm moving this to core-libs, please drop hotspot from any replies.

On 20/12/2013 6:26 AM, srikalyan wrote:
Hi all,  I have been working on the bug JDK-8022321
<https://bugs.openjdk.java.net/browse/JDK-8022321> , this is a sporadic
failure and the webrev is available here

I'm really not sure what to make of this. We have a test that triggers an out-of-memory condition but the OOME can actually turn up in the ReferenceHandler thread causing it to terminate and the test to fail. We previously accounted for the non-obvious occurrences of OOME due to the Object.wait and the possible need to load the InterruptedException class - but still the OOME can appear where we don't want it. So finally you have just placed the whole for(;;) loop in a try/catch(OOME) that ignores the OOME. I'm certain that makes the test happy, but I'm not sure it is really what we want for the ReferenceHandler thread. If the OOME occurs while cleaning, or enqueuing then we will fail to clean and/or enqueue but there would be no indication that has occurred and I think that is a bigger problem than this test failing.

There may be no way to make this test 100% reliable. In fact I'd suggest that no memory exhaustion test can be 100% reliable.


**"Root Cause:Still not known"*
2 places where there is a possibility for OOME
1) Cleaner.clean()
2) ReferenceQueue.enqueue()

1) The cleanup code in turn has 2 places where there is potential for
throwing OOME,
a) thunk Thread which is run from clean() method. This Runnable is
passed to Cleaner and appears in the following classes
However none of the above overridden implementations ever create an
object in the clean() code.
     b) new PrivilegedAction created in try catch Exception block of
clean() method but for this object to be created and to be held
responsible for OOME an Exception(other than OOME) has to be thrown.

2) No new heap objects are created in the enqueue method nor anywhere in
the deep call stack (VM.addFinalRefCount() etc) so this cannot be a
potential cause.

*Experimental change to java.lang.Reference.java* :
- Put one more guard (try catch with OOME block) in the Reference
Handler Thread which may give the Reference Handler a chance to cleanup.
This is fixing the test failure (several 1000 runs with 0 failures)
- Without the above change the test fails atleast 3-5 times for every
1000 run.

*PS*: The code change is to a very critical part of JDK and i am fully not aware of the consequences of the change, hence seeking expert help
here. Appreciate your time and inputs towards this.

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