Eclipse not stopping at java breakpoints during remote debug

Question

I'm running into a really strange error when trying to debug an application deployed to a jetty (9.4) server. I followed the instructions here: https://www.eclipse.org/jetty/documentation/jetty-9/index.html#advanced-debugging for setting up remote debugging with eclipse. I added the debugging arguments to my startup script and if I make a status call on jetty I can see them listed:

RUN_CMD = /opt/java/8/bin/java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=9999 -Djetty.home=/opt/jetty/9.4 -Djetty.base=/opt/web/jetty -Djava.io.tmpdir=/opt/jetty/temp -jar /opt/jetty/9.4/start.jar jetty.http.host=my ip adr jetty.http.port=my port jetty.spdyPort=my spd port jetty.state=/opt/web/jetty/jetty.state jetty-started.xml

If I run my start script it will pause and wait for me to launch the eclipse debugger before continuing. If I navigate to my app in the browser, I can see from the log output that my methods are running. However, breakpoints inside those methods are never getting hit and the execution never pauses.

I have tried everything I can think of and I just cannot see what I am doing wrong here. I've done this before and it worked, so I can only assume it is something about the way my application is deployed to jetty. Any suggestions would be appreciated.

UPDATE: I have narrowed down what I think is the source of the problem, but I still don't know how to fix it. I recently switched the logging module for jetty from log4j to logback. As soon as I disabled the logback module the debugging worked again. Unfortunately, simply disabling logging is not a long term solution. I still need some way of being able to debug AND have logging enabled.

Can you create a break on the method itself (right click it in the panel)? — Thorbjørn Ravn Andersen, Dec 15 '21 at 20:35
@ThorbjørnRavnAndersen I tried adding a method breakpoint but the outcome was the same. The only major changes I can think of would be switching the logging implementation from log4j to logback, but I can't see why that would interfere with eclipse breakpoints. — pbuchheit, Dec 15 '21 at 20:46
Is it just a problem with existing breakpoints, or do ones added *after* connecting properly halt? — nitind, Dec 15 '21 at 20:50
@ nitind It never stops at the breakpoints, it doesn't matter when I add them. — pbuchheit, Dec 15 '21 at 20:53
@ ThorbjørnRavnAndersen @ nitind Remember when I said I switched to logback, but that couldn't be the cause? Turns out that was in fact the cause. I still don't know WHY using logback would cause problems or what to do to fix this other than disabling my logging module. — pbuchheit, Dec 16 '21 at 16:54
can this help? https://stackoverflow.com/questions/44232723/intellij-remote-debugger-connects-but-breakpoints-are-not-working — murtiko, Dec 16 '21 at 18:05

pbuchheit · Answer 1 · 2021-12-17T15:59:16.437

Thanks to the jetty community I was finally able to track down an answer. See this thread: https://github.com/eclipse/jetty.project/issues/7299 for more details, but the short answer is that it was a jvm forking issue, similar to the question murtiko suggested.

Using any logging framework other than the basic slf4j-impl causes a jvm fork and requires a different approach to make the debugging work. Rather than specifying the debug arguments (-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=9999 ) in the setup script, they need to be set in the start.ini along with the --exec flag. something like:

# --------------------------------------- 
# Module: logging-logback
# Configure jetty logging to use Logback Logging.
# SLF4J is used as the core logging mechanism.
# --------------------------------------- 
--module=logging-logback

--exec
-Xdebug
-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=9999

If you don't want to have to edit the start.ini every time you want to turn debugging on or off, you can create a custom jetty module instead. I created a file called remote-debug.mod in $JETTY_HOME/modules with the contents

[exec]
-Xdebug
-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=9999

To enable debugging I simply have to add the argument --module=remote-debug to the startup command.

Eclipse not stopping at java breakpoints during remote debug

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