Debugging v2.0 With Chronon

1. December, 2011

“… Okay, let’s just set a breakpoint there … run again … continue continue continue next next next *argh* run again … continue continue continue next next … Why is it still null?? Who changes this field? Oh, damn … breakpoint … run again … where is that coming from? … oh no …”

Sound familiar? How often do you rerun your code just because you can’t step backwards in time? How often did you ask yourself “who is calling this method?” Or “where did this value come from?”

Meet Chronon. In a nutshell, Chronon runs your code, saves all state changes (method calls, variable assignments) somewhere and allows you to browse the result.

So with this tool, the text above would have been: “… Okay, it’s null here. Where does that value come from? *click* Oh, ok. Who called this method? *click* Oh, I see.”

This makes you find the source of an error much more quickly. Other questions that Chronon can answer:

  • Find all instances of a class that were created. A special window lists all exceptions that were thrown.
  • Step backwards (just like stepping forward)
  • Go to the code that printed a certain output on the Console (just click on the output in the Console window!)
  • Show me all the values of some variable (Post Execution Logging)

The tool is surprisingly fast. You’d expect something like that to hog your computer but collecting the data is pretty quick (just a small increase in the time it takes to execute the code; I didn’t time it).

It does take a mental leap, though. Stop thinking like you were executing the code. It’s more a specialized database browser where the data is all the states of your application.

Things that I don’t like:

  1. Opening a recording takes a few moments (<< 1 minute) while it “decompresses” the recording. I’m not sure what happens here. It seems stupid to compress the latest recording because chances are that you probably want to use it soon. But I guess this stage creates a couple of indexes so the UI can quickly navigate the data, so it’s just an unhappy label.
  2. The plug-in messes with my eclipse.ini! Bad plug-in, down! I understand that Chronon needs lots of RAM. And I think it does take your total memory into account (it allocated 2.5GB of my 8GB). Still, it should ask before doing something like that. And it absolutely should not do it again, after I reset the values to something sane. GCing 2.5GB of RAM does take a long time!

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