On 01/17/2014 02:00 PM, Peter Levart wrote:
On 01/17/2014 05:38 AM, David Holmes wrote:
On 17/01/2014 1:31 PM, srikalyan chandrashekar wrote:
Hi David, the disassembled code is also attached to the bug. Per my

Sorry missed that.

analysis the exception was thrown when Reference Handler was on line 143
as put in the earlier email.

But if the numbers in the dissassembly match the BCI then 65 shows:

      65: instanceof    #11                 // class sun/misc/Cleaner

which makes more sense, the runtime instanceof check might encounter an OOME condition. I wish there was some easy way to trace into the full call chain as TraceExceptions doesn't show you any runtime frames :(

Still, it is easy enough to check:

// Fast path for cleaners
boolean isCleaner = false;
try {
  isCleaner = r instanceof Cleaner;
} catch (OutofMemoryError oome) {

if (isCleaner) {

Hi David, Kalyan,

I've caught-up now. Just thinking: is "instanceof Cleaner" throwing OOME as a result of loading the Cleaner class? Wouldn't the above code then throw some error also in ((Cleaner)r) - the checkcast, since Cleaner class would not be successfully initialized?

Well, no. The above code would just skip Cleaner processing in this situation. And will never be doing it again after the heap is freed... So it might be good to load and initialize Cleaner class as part of ReferenceHandler initialization to ensure correct operation...


Perhaps we should pre-load and initialize the Cleaner class as part of ReferenceHandler initialization...

Regards, Peter



On 1/16/14 6:16 PM, David Holmes wrote:
On 17/01/2014 4:48 AM, srikalyan wrote:
Hi David

On 1/15/14, 9:04 PM, David Holmes wrote:
On 16/01/2014 10:19 AM, srikalyan chandrashekar wrote:
Hi Peter/David, we could finally get a trace of exception with
build and ReferenceHandler modified (with runImpl() added and called
from run()). The logs, disassembled code is available in JIRA
<https://bugs.openjdk.java.net/browse/JDK-8022321> as attachments.

All I can see is the log for the OOMECatchingTest program not one for
the actual ReferenceHandler ??

Please search for ReferenceHandler in the log.
Observations from the log:

Root Cause:
1) UncaughtException is being dispatched from Reference.java:143
141                   Reference<Object> r;
142                   synchronized (lock) {
143                        if (pending != null) {
144                            r = pending;
145                            pending = r.discovered;
146                            r.discovered = null;

pending field in Reference is touched and updated by the collector, so at line 143 when the execution context is in Reference handler there
might have been an Exception pending due to allocation done by
which causes ReferenceHandler thread to die.

Sorry but the GC does not trigger asynchronous exceptions so this
explanation does not make any sense to me. What part of the log led
you to this conclusion?
------------------ Log Excerpt begins ------------------
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff7808e8)

line 168]
for thread 0x00007feed80cf800
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff7808e8)
thrown in interpreter method <{method} {0x00007feeddd3c600} 'runImpl'
'()V' in 'java/lang/ref/Reference$ReferenceHandler'>
  at bci 65 for thread 0x00007feed80cf800
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff7808e8)
  thrown in interpreter method <{method} {0x00007feeddd3c478} 'run'
'()V' in 'java/lang/ref/Reference$ReferenceHandler'>
  at bci 1 for thread 0x00007feed80cf800
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff780868)

line 157]
for thread 0x00007feed80cf800
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff780868)
  thrown in interpreter method <{method} {0x00007feeddcaaf90}
'uncaughtException' '(Ljava/lang/Thread;Ljava/lang/Throwable;)V' in '>
  at bci 48 for thread 0x00007feed80cf800
Exception <a 'java/lang/OutOfMemoryError'> (0x00000000ff780868)
  thrown in interpreter method <{method} {0x00007feeddca7298}
'dispatchUncaughtException' '(Ljava/lang/Throwable;)V' in 'java/lang/>
  at bci 6 for thread 0x00007feed80cf800
------------------ Log Excerpt ends ------------------
Sorry if it is a wrong understanding.

What you are seeing there is an OOME escaping the run() method which
will cause the uncaughtExceptionHandler to be run which then triggers
a second OOME (likely as it tries to report information about the
first OOME). The first exception occurred in runImpl at BCI 65. Can
you disassemble (javap -c) the class you used so we can see what is at
BCI 65.


Suggested fix:
- As proposed earlier putting an outer guard(try-catch on OOME) in the ReferenceHandler will fix the issue, if ReferenceHandler is considered as part of the GC sub system then it should be alive even in the midst
of an OOME so i feel that the additional guard should be allowed,
however i might still be ignorant of vital implications.
- Apart from the above changes, Peter's suggestion to create and
call a
private runImpl() from run() in ReferenceHandler makes sense to me.

Why would we need this?



On 01/13/2014 03:57 PM, srikalyan wrote:

On 1/11/14, 6:15 AM, Peter Levart wrote:

On 01/10/2014 10:51 PM, srikalyan chandrashekar wrote:
Hi Peter the version you provided ran indefinitely(i put a 10
timeout) and the program got interrupted(no error),

Did you run it with or without fastedbug & -XX:+TraceExceptions ? If with, it might be that fastdebug and/or -XX:+TraceExceptions changes
the execution a bit so that we can no longer reproduce the wrong
With fastdebug & -XX:TraceExceptions. I will try combination of
possible options(i.e without -XX:TraceEception on debug build etc)

even if there were to be an error you cannot print the "string" of
thread to console(these have been attempted earlier).

...it has been attempted to print toString in uncaught exception
handler. At that time, the heap is still full. I'm printing it after the GC has cleared the heap. You can try that it works by commenting
out the "try {" and corresponding "} catch (OOME x) {}" exception
Since there is a GC call prior to printing string i will give that a
shot with non-debug build.

- The test's running on interpreter mode, what i am watching for is
one error with trace. Without fastdebug build and
-XX:+TraceExceptions i am able to reproduce failure atleast 5
failures out of 1000 runs but with fastdebug+Trace no luck
yet(already past few 1000 runs).

It might be interesting to try with fastebug build but without the
-XX:+TraceExceptions option to see what has an effect on it. It
also be interesting to try the modified ReferenceHandler (the one
with private runImpl() method called from run()) and with normal
non-fastdebug JDK. This info might be useful when one starts to
inspect the exception handling code in interpreter...

Regards, Peter

Ph: (408)-585-8040


On 01/10/2014 02:57 AM, Peter Levart wrote:
On 01/10/2014 09:31 AM, Peter Levart wrote:
Since we suspect there's something wrong with exception handling in interpreter, I devised a hypothetical reproducer that tries to simulate ReferenceHandler in many aspects, but doesn't require to
be a ReferenceHandler:


This is designed to run indefinitely and only terminate if/when thread dies. Could you run this program in the environment that
causes the OOMEInReferenceHandler test to fail and see if it

I forgot to mention that in order for this long-running program to exhibit interpreter behaviour, it should be run with -Xint option.
So I suggest:

-Xmx24M -XX:-UseTLAB -Xint

Regards, Peter

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