First, I should note that I am not an expert on C$SOCKET, but I have used it, so I figure my skill level is intermediate.

Without blocking?  Effectively.  Technically, it will block for the timeout value when there is no data waiting to be read, but keep that small and you hardly block at all.  When waiting for a connection, keep the timeout small and add a sleep when nothing happens, to avoid wasting time just waiting for connection(s).  Please note, this assumes that your server side stuff needs to run while waiting for a connection.  You could simplify things if the server side required the client to be running/connected in order to do anything, but I think you would be better off letting the client disconnect/reconnect as needed.

With the AGS-READ, you can choose to block for a small timeout, or use the zero-size read trick to check for data, then read only that amount of data.  This results is a zero-wait read with a test/read (technically 2 reads, one to test for data, one to get it).  Given that this is a replacement for checking for messages, that should work.  (Warning: Since the packets could have only part of the message due to network traffic optimization etc, you will also have to test if the message is completely received, or if you have to save what you have so far, treat the message as not received yet, and check for more the next time you check for the message.  And handle a dropped connection by resetting the buffer info, and changing your internal flags that mark the connection as on or off.  You know, programming stuff.)

First, I should note that I am not an expert on C$SOCKET, but I have used it, so I figure my skill level is intermediate.

Without blocking?  Effectively.  Technically, it will block for the timeout value when there is no data waiting to be read, but keep that small and you hardly block at all.  When waiting for a connection, keep the timeout small and add a sleep when nothing happens, to avoid wasting time just waiting for connection(s).  Please note, this assumes that your server side stuff needs to run while waiting for a connection.  You could simplify things if the server side required the client to be running/connected in order to do anything, but I think you would be better off letting the client disconnect/reconnect as needed.

With the AGS-READ, you can choose to block for a small timeout, or use the zero-size read trick to check for data, then read only that amount of data.  This results is a zero-wait read with a test/read (technically 2 reads, one to test for data, one to get it).  Given that this is a replacement for checking for messages, that should work.  (Warning: Since the packets could have only part of the message due to network traffic optimization etc, you will also have to test if the message is completely received, or if you have to save what you have so far, treat the message as not received yet, and check for more the next time you check for the message.  And handle a dropped connection by resetting the buffer info, and changing your internal flags that mark the connection as on or off.  You know, programming stuff.)

THANK YOU, this is extremely helpful - exactly what we need.

Yes, I have decades of experience around performance and responsiveness. I know we have to sleep in every loop, and keep these blocks under a few milliseconds so we can respond to other demands quickly. And I know that socket messages can be received in pieces. But I am not sure I would have figured out the "zero-size read trick". Thanks for that, too.

I wish I had understood years ago the runtime has the ability to do socket communications without blocking. I swear I consulted Acucobol (the company name at the time) when we implemented this. But I have looked back to the 8.1.3 release notes and the documentation is the same as it is now, so I don't think this has changed.

Again, thank you!