The application master launcher has a thread pool that is configured with core size 1, maximum 10. The thread pool will not create over
the core size thread unless the queue it is using is full. We are using an unbounded queue, so the thread pool will only ever create 1 thread. We need to have more then 1 AM launch thread.
If that thread becomes hung for some reason, the RM can no longer launch any application masters. We have seen an instance of this when a NM become unresponsive - something bad happened to host, not sure what yet.