AsynApender stop appending Logs when RingBuffer is full

[noorulhaq]

Hi,

If the subscriber is unable to write logs because of any reason the logger doAppend stuck in an infinite waiting loop because the writer cannot surpass the reader. Below is the is the thread dump captured in that moment.

java.lang.Thread.State: WAITING
	  at sun.misc.Unsafe.park(Unsafe.java:-1)
	  at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:338)
	  at reactor.core.publisher.MultiProducerRingBuffer.next(RingBuffer.java:1850)
	  at reactor.core.publisher.MultiProducerRingBuffer.next(RingBuffer.java:1816)
	  at reactor.core.publisher.UnsafeRingBuffer.next(RingBuffer.java:1576)
	  at reactor.core.publisher.EventLoopProcessor.onNext(EventLoopProcessor.java:445)
	  at reactor.logback.AsyncAppender.queueLoggingEvent(AsyncAppender.java:238)
	  at reactor.logback.AsyncAppender.doAppend(AsyncAppender.java:104)
	  at reactor.logback.AsyncAppender.doAppend(AsyncAppender.java:46)
	  at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:48)
	  at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:273)
	  at ch.qos.logback.classic.Logger.callAppenders(Logger.java:260)
	  at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:442)
	  at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:396)
	  at ch.qos.logback.classic.Logger.debug(Logger.java:503)
	  at com.non.reactive.bank.Application.main(Application.java:18)

Also, below the code snippet where it stuck, taken from reactor RingBuffer:

@Override
	public long next(int n)
	{
		if (n < 1)
		{
			throw new IllegalArgumentException("n must be > 0");
		}

		long current;
		long next;

		do
		{
			current = cursor.getAsLong();
			next = current + n;

			long wrapPoint = next - bufferSize;
			long cachedGatingSequence = gatingSequenceCache.getAsLong();

			if (wrapPoint > cachedGatingSequence || cachedGatingSequence > current)
			{
				long gatingSequence = RingBuffer.getMinimumSequence(gatingSequences, current);

				if (wrapPoint > gatingSequence)
				{
					if(spinObserver != null) {
						spinObserver.run();
					}
					LockSupport.parkNanos(1); // TODO, should we spin based on the wait strategy?
					continue;
				}

				gatingSequenceCache.set(gatingSequence);
			}
			else if (cursor.compareAndSet(current, next))
			{
				break;
			}
		}
		while (true);

		return next;
	}

I can see that that the wait strategy is not being used to handle this situation. Is there any way to get out of this situation either by throwing any timeout exception or anything else rational. I know we may lose logs for some time but at least the requesting threads will not hang because of this issue.

[simonbasle]

closing as duplicate, kept #63 (please edit issues, you can even edit the title)