Analysis on JDK-8022321 java/lang/ref/OOMEInReferenceHandler.java fails intermittently

[Peter Levart]

On 01/21/2014 08:57 AM, David Holmes wrote:
>> [Loaded java.util.TimeZone from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> [Loaded sun.util.calendar.ZoneInfo from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> [Loaded sun.util.calendar.ZoneInfoFile from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> [Loaded sun.util.calendar.ZoneInfoFile$1 from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> [Loaded java.io.DataInput from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> [Loaded java.io.DataInputStream from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]
>> *[Loaded sun.misc.Cleaner from
>> /home/peter/Apps64/jdk1.8.0-ea-b121/jre/lib/rt.jar]*
>
> Curious. I wonder what the controlling factor is ?? 

The Cleaner is usually loaded by ReferenceHandler in JDK8 in the 1st 
execution of it's loop. It looks like JDK8 system initialization 
produces at least one XXXReference that is cleared before main() method 
is entered (debugging, I found it's a Finalizer for a FileInputStream - 
perhaps of the stream that loads the TimeZone data), so ReferenceHandler 
thread is woken-up, executes the instanceof Cleaner check and this loads 
the class. I put the following printfs in an original ReferenceHandler:

     System.out.println("Before using Cleaner...");
     // Fast path for cleaners
     if (r instanceof Cleaner) {
         ((Cleaner)r).clean();
         continue;
     }
     System.out.println("After using Cleaner...");


...and the empty main() test with -verbose:class prints:

...
[Loaded java.io.DataInput from 
/home/peter/work/hg/jdk8-tl/build/linux-x86_64-normal-server-release/images/j2sdk-image/jre/lib/rt.jar]
[Loaded java.io.DataInputStream from 
/home/peter/work/hg/jdk8-tl/build/linux-x86_64-normal-server-release/images/j2sdk-image/jre/lib/rt.jar]
*Before using Cleaner...**
**[Loaded sun.misc.Cleaner from out/production/jdk]**
**After using Cleaner...*
[Loaded java.io.ByteArrayInputStream from 
/home/peter/work/hg/jdk8-tl/build/linux-x86_64-normal-server-release/images/j2sdk-image/jre/lib/rt.jar]
[Loaded sun.util.calendar.ZoneInfoFile$ZoneOffsetTransitionRule from 
/home/peter/work/hg/jdk8-tl/build/linux-x86_64-normal-server-release/images/j2sdk-image/jre/lib/rt.jar]

...


But sometimes, It seems, the VM is not so quick in clearing the early 
XXXReferences and/or the ReferenceHandler start-up is delayed and the 
1st iteration of the loop is executed after the OOMEInReferenceHandler 
test already fills the heap and consequently loading of Cleaner class 
throws OOME in instanceof check...

My proposed fix is very aggressive. It pre-loads classes, initializes 
them and watches for OOMEs thrown in all ocasions. It might be that 
pre-loading Cleaner class in ReferenceHandler initialization would be 
sufficient to fix this intermittent failure. Or do you think instanceof 
check could throw OOME for some other reason besides loading of the class?


Regards, Peter