When the TCP Agent listener crashes, it prints:

2022-12-22 01:29:20.541+0000 [id=632]	WARNING	hudson.TcpSlaveAgentListener$1#run: Connection handler failed, restarting listener

However, it never seems to be restarted.

How to Reproduce

(thanks duemir for providing those steps)

It can be reproduced with a debugger (at least an IntelliJ one)

• Start a 2.375.1 Jenkins instance with debugger enabled
• Prepare the IDE
• Checkout tag jenkins-2.375.1 from the jenkinsci/jenkins repo
• Open hudson.TcpSlaveAgentListener
• Set breakpoint somewhere in the run method of the ConnectionHandler (line 279)
• Enable the TCP port
• Set up an inbound agent and test that it connects
• Connect the debugger to the controller
• Use Throw an exception to throw some exception that is not handled in the run, e.g. new IllegalStateException("BOOM")

As a result, something similar to the lines below should be printed in the controller logs

2022-12-22 01:29:20.540+0000 [id=632]	SEVERE	h.TcpSlaveAgentListener$ConnectionHandler#lambda$new$0: Uncaught exception in TcpSlaveAgentListener ConnectionHandler Thread[TCP agent connection handler #6 with /127.0.0.1:61392,5,main]
java.lang.IllegalStateException: BOOM
	at hudson.TcpSlaveAgentListener$ConnectionHandler.run(TcpSlaveAgentListener.java:280)
2022-12-22 01:29:20.541+0000 [id=632]	WARNING	hudson.TcpSlaveAgentListener$1#run: Connection handler failed, restarting listener
java.lang.IllegalStateException: BOOM
	at hudson.TcpSlaveAgentListener$ConnectionHandler.run(TcpSlaveAgentListener.java:280)

May need to fiddle a bit with a breakpoint (it didn't work the first time for me for some reason. I ended up with a breakpoint that only suspended a Thread, and I had to do the "Throw exception" action twice)

Expected: As the log says, the TCP Agent listener is restarted after the crash
Actual: It is not. The Port is not up, and agents cannot connect.

The workaround is to disable the port and then enable it again.