Using JITWatch programmatically (API usage instead of UI)

[c71n93]

Hi!
I’m exploring the possibility of using JITWatch programmatically — as a library — to automatically analyze HotSpot JIT logs (e.g., extract compiled method info, main code size, inlining data, etc.), rather than through the UI.

Before diving too deep, I’d like to clarify:

1. Was it ever intended by design that JITWatch could be used directly as an API/library (for example, via classes like LogParser, JITDataModel, NMethod, AssemblyMethod, etc.)?
2. Are there any existing examples, documentation, or recommended patterns for using JITWatch this way?
   I’ve checked some sources but only found materials related to the UI, not API usage.

Thanks in advance — I’d like to understand whether such usage is supported or considered out of scope for JITWatch.

[chriswhocodes]

Hi Roman,

Yes, the source code is split into 2 sub-projects, core and ui. You can call the APIs in core without using the ui classes.

Check out the class org.adoptopenjdk.jitwatch.launch.LaunchHeadless in the core tree.

Kind regards,

Chris

[c71n93]

@chriswhocodes Thanks a lot for your answer!

Could you please tell me if there is any documentation or example code demonstrating how to use the core API?
I haven’t been able to find any so far. Browsing the source and experimenting may eventually work, but I’d really appreciate knowing if there are any official or reliable references on how to use the JITWatch API programmatically.

Thanks again!

[chriswhocodes]

Hi Roman,

Did you check the wiki? https://github.com/AdoptOpenJDK/jitwatch/wiki/Headless-Mode

The source code for https://github.com/AdoptOpenJDK/jitwatch/blob/master/core/src/main/java/org/adoptopenjdk/jitwatch/launch/LaunchHeadless.java is pretty clear on how to load the log file into the parser, handle JIT events, and produce a report.

I'd be happy to accept a PR if you would like to improve the documentation.

Kind regards,

Chris

[c71n93]

@chriswhocodes Thank you, Chris.

Wiki https://github.com/AdoptOpenJDK/jitwatch/wiki/Headless-Mode is helpful, but it’s not exactly what I’m looking for. My goal is to use JITWatch as a library within my own Java application, so I’m mainly interested in documentation about the following:

• How to include JITWatch as an external dependency (via Maven or Gradle).
• Which parts of the core module are considered stable API and safe for external use, so I don’t rely on internal implementation details that may change.
• Example code showing how the API is typically intended to be used, since otherwise I’d need to explore the JITWatch source to infer that myself.

Thanks to your explanations, I’m now confident that I can experiment with integrating JITWatch into my project. I’ll start by studying the code in https://github.com/AdoptOpenJDK/jitwatch/blob/master/core/src/main/java/org/adoptopenjdk/jitwatch/launch/LaunchHeadless.java, and once I get things working, I’d be glad to contribute documentation covering these points above.