https://github.com/ktoso/sbt-jol

Don't guess JVM object sizes. Get them on a silver platter.
https://github.com/ktoso/sbt-jol

Last synced: 2 months ago
JSON representation

Don't guess JVM object sizes. Get them on a silver platter.

• Host: GitHub
• URL: https://github.com/ktoso/sbt-jol
• Owner: ktoso
• Created: 2015-09-22T15:03:12.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2020-12-14T13:45:52.000Z (about 4 years ago)
• Last Synced: 2024-10-25T06:07:52.161Z (3 months ago)
• Language: Scala
• Homepage:
• Size: 16.6 KB
• Stars: 87
• Watchers: 9
• Forks: 7
• Open Issues: 5
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

README

        
# sbt-jol

[ ![Download](https://api.bintray.com/packages/ktosopl/sbt-plugins/sbt-jol/images/download.svg) ](https://bintray.com/ktosopl/sbt-plugins/sbt-jol/_latestVersion)

Trivial way to inspect OpenJDK's [*Java Object Layout*](http://openjdk.java.net/projects/code-tools/jol/) of your Scala classes.

Get the latest via:

 ```

 // project/plugins.sbt

 addSbtPlugin("pl.project13.sbt" % "sbt-jol" % pluginVersionHere)

 ```

 

 Which allows you to (note auto-completion works nicely):

 

 ```

 > jol:internals example.Entry

 

[info] # Running 64-bit HotSpot VM.

[info] # Using compressed oop with 3-bit shift.

[info] # Using compressed klass with 3-bit shift.

[info] # WARNING | Compressed references base/shifts are guessed by the experiment!

[info] # WARNING | Therefore, computed addresses are just guesses, and ARE NOT RELIABLE.

[info] # WARNING | Make sure to attach Serviceability Agent to get the reliable addresses.

[info] # Objects are 8 bytes aligned.

[info] # Field sizes by type: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]

[info] # Array element sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 [bytes]

[info]

[info] VM fails to invoke the default constructor, falling back to class-only introspection.

[info]

[info] example.Entry object internals:

[info]  OFFSET  SIZE   TYPE DESCRIPTION                    VALUE

[info]       0    12        (object header)                N/A

[info]      12     4    int Entry.value                    N/A

[info]      16     4 String Entry.key                      N/A

[info]      20     4        (loss due to the next object alignment)

[info] Instance size: 24 bytes

[info] Space losses: 0 bytes internal + 4 bytes external = 4 bytes total

 ```

 

  Currently uses jol `0.5`.

Contribute!

-----------

Please note that this plugin is mostly developed on a "on demand" basis by and for myself, contributions are very (!) welcome 

since I most likely will not focus much on it unless I need more features (and for now estimates and internal are all I needed).

 

 License

 -------

 

 Apache v2