(Preliminary) RFC 7038914: VM could throw uncaught OOME in ReferenceHandler thread

Peter Levart peter.levart at gmail.com
Mon May 6 20:34:26 UTC 2013


On 05/06/2013 10:02 AM, Thomas Schatzl wrote:
> I mean, if we fix this issue as you suggested (I am not against that, it
> looks reasonable), I would not know what to do with the test program
> except file another bug against the very same component with the same
> problem, with the same fix suggestion.

Hi Thomas,

If you want a simple reproducer for OOME in ReferenceHandler's 
Object.wait(), here is one:


public class OOMEInReferenceHandler {

     static Object[] fillHeap() {
         Object[] first = null, last = null;
         int size = 1 << 20;
         while (size > 0) {
             try {
                 Object[] array = new Object[size];
                 if (first == null) {
                     first = array;
                 }
                 else {
                     last[0] = array;
                 }
                 last = array;
             }
             catch (OutOfMemoryError oome) {
                 size = size >>> 1;
             }
         }
         return first;
     }

     public static void main(String[] args) throws Exception {
         ReferenceQueue<Object> refQueue = new ReferenceQueue<Object>();
         Object referent = new Object();
         WeakReference<Object> weakRef = new 
WeakReference<Object>(referent, refQueue);

         ThreadGroup tg = Thread.currentThread().getThreadGroup();
         for (ThreadGroup tgn = tg;
              tgn != null;
              tg = tgn, tgn = tg.getParent());

         Thread[] threads = new Thread[tg.activeCount()];
         Thread referenceHandlerThread = null;
         int n = tg.enumerate(threads);
         for (int i = 0; i < n; i++) {
             if("Reference Handler".equals(threads[i].getName())) {
                 referenceHandlerThread = threads[i];
             }
         }

         if (referenceHandlerThread == null) {
             throw new IllegalStateException("Couldn't find Reference 
Handler thread.");
         }

         Object waste = fillHeap();

         referenceHandlerThread.interrupt();

         Thread.sleep(1000L);
         waste = null;
         referent = null;
         System.gc();
         Thread.sleep(1000L);

         System.out.println("weakRef.get() = " + weakRef.get());
         System.out.println("refQueue.poll() = " + refQueue.poll());
     }
}



... just run it with some low heap setting like -Xmx128m or so. It 
doesn't need to be G1 garbage collector. Default will do.

This prints on my computer:

Exception: java.lang.OutOfMemoryError thrown from the 
UncaughtExceptionHandler in thread "Reference Handler"
weakRef.get() = null
refQueue.poll() = null


Regards, Peter



Regards, Peter

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