Question

I have an application that executes some heavy processing in background using java thread pools.

Thread pool are configured to log exceptions occurred during the execution

public enum ExceptionLogger implements Thread.UncaughtExceptionHandler {
    INSTANCE;

    private static final Logger log = LoggerFactory.getLogger(ExceptionLogger.class);

    @Override
    public void uncaughtException(Thread t, Throwable e) {
        log.error("Exception occurred at thread " + t.getName() + "\n", e);
    }
  }

In the logs of my application I’m randomly getting java.lang.OutOfMemoryError: Java heap space but if I log memory usage using Runtime.getRuntime().freeMemory() I can see plenty of free heap space available.

In addition application continues working after I get this exception.

Is there any other reason for getting OutOfMemoryError with this message?

Answer 1

You will get an OutOfMemoryError when memory fails to allocate.

This can happen when

• you have run out of memory.
• your GC turning parameters prevent it from using all the memory. e.g. setting minimum sizes for generations which are not full.
• you allocate a large block of memory. Immediately after this fails you still have free memory, just not enough to allocate the large block.
• you get an OutOfMemoryError which is not for the heap, e.g. PermGen or direct memory or virtual memory (for threads etc)