Thank you so much. with selectNow, Not blocked. My program was in while (true) {...;readCount = selector.select();...;}, but to short the code for post in this group, make one call to see if it can go through. I am working based on a very old app, it was NIO no-block with org.xsocket. call selector.select(), so I took it, but upgraded the dependencies, replace org.xsocket with java.nio. your are great!! Thank you again,