Thread blocked in TextEncoderHelper copyDataToDestination - log4j2

Question

I'm debugging my code and I see my thread is being blocked in the following log4j TextEncoderHelper. I'm using log4j 2.8.2
None of my threads was able to run and it basically blocked the whole application.
Does anyone know what the below does? If I have two threads logging, does it mean its deadlock?
(I'm running with parameter
-DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector -DAsyncLogger.RingBufferSize=32768*32768 -DAsyncLogger.WaitStrategy=Sleep -Dlog4j2.AsyncQueueFullPolicy=Discard)
private static void copyDataToDestination(final ByteBuffer temp, final ByteBufferDestination destination) {
61 synchronized (destination) {
62 ByteBuffer destinationBuffer = destination.getByteBuffer();
63 if (destinationBuffer != temp) { // still need to write to the destination
64 temp.flip();
65 if (temp.remaining() > destinationBuffer.remaining()) {
66 destinationBuffer = destination.drain(destinationBuffer);
67 }
68 destinationBuffer.put(temp);
69 temp.clear();
70 }
71 }
72 }

Answer 1

If the debugger shows the application is blocked trying to write to the underlying appender then perhaps the underlying appender cannot keep up with the workload.
The question doesn’t mention what appender is being used so I initially assumed the file appender but from the comments it turns out the JmsAppender is used. (Please mention details like this in future questions: without this information I was thinking in the wrong direction.)
JMS is a big subject by itself but is generally not known for being highly performant. The actual throughput that can be achieved depends on the implementation product and its configuration.
I suggest enabling JMS debug options to confirm that the JMS queue is indeed the bottleneck.