question: public void messageArrived ( MqttPublish sendMessage ) { final String methodName = "messageArrived" ; if ( mqttCallback != null || callbacks . size ( ) > 0 ) { synchronized ( spaceAvailable ) { while ( running && ! quiescing && messageQueue . size ( ) >= INBOUND_QUEUE_SIZE ) { try { log . fine ( CLASS_NAME , methodName , "709" ) ; spaceAvailable . wait ( 200 ) ; } catch ( InterruptedException ex ) { } } } if ( ! quiescing ) { messageQueue . addElement ( sendMessage ) ; synchronized ( workAvailable ) { log . fine ( CLASS_NAME , methodName , "710" ) ; workAvailable . notifyAll ( ) ; } } } }
target:  This method is called when a message arrives on a topic. Messages are only added to the queue for inbound messages if the client is not quiescing.