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 mySorry missed that.analysis the exception was thrown when Reference Handler was on line 143as put in the earlier email.But if the numbers in the dissassembly match the BCI then 65 shows: 65: instanceof #11 // class sun/misc/Cleanerwhich 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) { continue; } if (isCleaner) { ((Cleaner)r).clean(); continue; }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...
Peter
Perhaps we should pre-load and initialize the Cleaner class as part of ReferenceHandler initialization...Regards, PeterThanks, David-- Thanks kalyan 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 fastdebugbuild and ReferenceHandler modified (with runImpl() added and calledfrom 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 forthe 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 theremight have been an Exception pending due to allocation done by collector 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) thrown[/home/srikalyc/work/ora2013/infracleanup/jdk8/hotspot/src/share/vm/gc_interface/collectedHeap.inline.hpp,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) thrown[/home/srikalyc/work/ora2013/infracleanup/jdk8/hotspot/src/share/vm/gc_interface/collectedHeap.inline.hpp,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. Thanks, DavidSuggested 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 midstof 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? David -------- Thanks kalyan 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 minute 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 changesthe execution a bit so that we can no longer reproduce the wrong behaviour.With fastdebug & -XX:TraceExceptions. I will try combination of possible options(i.e without -XX:TraceEception on debug build etc) soon.Since there is a GC call prior to printing string i will give that aeven if there were to be an error you cannot print the "string" ofthread to console(these have been attempted earlier)....it has been attempted to print toString in uncaught exceptionhandler. 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 commentingout the "try {" and corresponding "} catch (OOME x) {}" exception handler...shot with non-debug build.- The test's running on interpreter mode, what i am watching for isone 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 might 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-- Thanks kalyan Ph: (408)-585-8040--- Thanks kalyan 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 tobe a ReferenceHandler:http://cr.openjdk.java.net/~plevart/misc/OOME/OOMECatchingTest.javaThis is designed to run indefinitely and only terminate if/when thread dies. Could you run this program in the environment thatcauses the OOMEInReferenceHandler test to fail and see if it terminates?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
