Operating System and Platform

Oct 13, 2025 by pinkandtrash.com 25 views

Introduction

In this article, we will explore an issue with JRuby's TracePoint feature, specifically when using the :call event and the --debug flag. We will examine a small code snippet that demonstrates the problem and discuss the expected and actual behavior.

The Problem

The issue arises when tracing code with :call and using the --debug flag. The code snippet below illustrates the problem:

t = TracePoint.new(:call) do |tp|
end
t.enable

def some_method(a, b: true)
  p [:a, a, b]
end

some_method(10, b: 20)

When run with jruby foo.rb, the code works as expected, printing [:a, 10, 20] to the screen. However, when run with jruby --debug foo.rb, the code crashes with an ArgumentError:

ArgumentError: wrong number of arguments (given 2, expected 1)
  some_method at /tmp/foo.rb:6
       <main> at /tmp/foo.rb:9

Expected Behavior

The expected behavior is that both with and without the --debug flag, the result should be [:a, 10, 20] printed to the screen.

Actual Behavior

The actual behavior is that with the --debug flag, the code crashes with an ArgumentError.

Investigation

To investigate this issue, we will examine the JRuby version and operating system used.

JRuby Version

The JRuby version used is jruby 9.4.12.0 (3.1.4) 2025-02-11 f4ab75096a OpenJDK 64-Bit Server VM 20.0.2+9-78 on 20.0.2+9-78 +jit [x86_64-linux].

Operating System and Platform

The operating system and platform used are Ubuntu 22.04, x86_64.

Conclusion

In conclusion, tracing :call with TracePoint and the --debug flag makes kwargs unusable in JRuby. This issue is specific to the :call event and the --debug flag. The expected behavior is that the code should work with and without the --debug flag, but the actual behavior is that the code crashes with an ArgumentError when run with the --debug flag.

Workaround

A workaround for this issue is to comment out the lines that enable the TracePoint, as shown below:

# t = TracePoint.new(:call) do |tp|
# end
# t.enable

This will allow the code to run with the --debug flag without crashing.

Future Development

This issue should be addressed in future versions of JRuby. In the meantime, developers can use the workaround mentioned above to avoid this issue.

Recommendations

Developers using JRuby should be aware of this issue and take necessary precautions when using the :call event and the --debug flag. The workaround mentioned above can be used to avoid this issue.

Additional Information

For more information on JRuby and its features, please refer to the official JRuby documentation.

References

JRuby documentation: https://jruby.org/documentation/
TracePoint documentation: https://jruby.org/docs/jruby-9.4.12.0/html/tracepoint.html

Acknowledgments

The author would like to thank the JRuby community for their contributions and support.

License

Introduction

In our previous article, we explored an issue with JRuby's TracePoint feature, specifically when using the :call event and the --debug flag. We examined a small code snippet that demonstrated the problem and discussed the expected and actual behavior. In this article, we will answer some frequently asked questions (FAQs) related to this issue.

Q: What is the issue with tracing `:call` with TracePoint and the `--debug` flag?

A: The issue is that tracing :call with TracePoint and the --debug flag makes kwargs (keyword arguments) unusable in JRuby. This means that when you use the :call event and the --debug flag, any code that uses kwargs will crash with an ArgumentError.

Q: What is the expected behavior?

A: The expected behavior is that both with and without the --debug flag, the code should work as expected, without crashing.

Q: What is the actual behavior?

A: The actual behavior is that with the --debug flag, the code crashes with an ArgumentError.

Q: What is the workaround for this issue?

A: A workaround for this issue is to comment out the lines that enable the TracePoint, as shown below:

# t = TracePoint.new(:call) do |tp|
# end
# t.enable

This will allow the code to run with the --debug flag without crashing.

Q: Is this issue specific to the `:call` event and the `--debug` flag?

A: Yes, this issue is specific to the :call event and the --debug flag. Other events and flags may not exhibit this behavior.

Q: Can I use kwargs with other events and flags?

A: Yes, you can use kwargs with other events and flags. The issue is specific to the :call event and the --debug flag.

Q: How can I avoid this issue?

A: To avoid this issue, you can use the workaround mentioned above, or you can avoid using the :call event and the --debug flag altogether.

Q: Is this issue fixed in future versions of JRuby?

A: This issue should be addressed in future versions of JRuby. However, until then, developers should be aware of this issue and take necessary precautions.

Q: Where can I find more information on JRuby and its features?

A: You can find more information on JRuby and its features in the official JRuby documentation.

Q: Can I contribute to the JRuby project?

A: Yes, you can contribute to the JRuby project by reporting issues, submitting patches, or participating in the JRuby community.

Conclusion

In conclusion, tracing :call with TracePoint and the --debug flag makes kwargs unusable in JRuby. This issue is specific to the :call event and the --debug flag. We hope that this Q&A article has provided you with the information you need to understand and work around this issue.

Additional Resources

JRuby documentation: https://jruby.org/documentation/
TracePoint documentation: https://jruby.org/docs/jruby-9.4.12.0/html/tracepoint.html
JRuby community: https://jruby.org/community/

License

This article is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License.