[manum]

Hi, I'm the author of that post. If a thread is not available from the pool the calling thread tries to execute the operation itself. That allows the bolt to continue making progress but adds a simple back pressure mechanism.

This also avoids the overhead of any sort of locking to wait for a thread to be free. Since the number of bolt executors will always be much less than the number of threads in the IO pool it doesn't add too much the concurrency overall. Hope that makes sense.