RFR(M): JDK-8059036 : Implement Diagnostic Commands for heap and finalizerinfo

[Staffan Larsen]

Dmitry,

I think this should be reviewed on hotspot-gc and core-libs-dev as well considering the changes to Finalizer.

I’m a little worried about the potentially very large String that is returned from printFinalizationQueue(). A possible different approach would be to write printFinalizationQueue() in C++ inside Hotspot. That would allow for outputting one line at a time. The output would still be saved in memory (since the stream is buffered), but at least the data is only saved once in memory, then. It would make the code a bit harder to write, so its a question of how scared we are of running out of memory.

I see you are traversing the ‘unfinalized’ list in Finalizer, whereas the old SA code for ‘-finalizerinfo' traverses the ‘queue’ list. I am not sure of the difference, perhaps someone from the GC team can help out?

For the output, it would be a nice touch to sort it on the number of references for each type. Perhaps outputting it more like a table (see the old code again) would also make it easier to digest.

In diagnosticCommand.hpp, the new commands should override permission() and limit access:

  static const JavaPermission permission() {
    JavaPermission p = {"java.lang.management.ManagementPermission",
                        "monitor", NULL};
    return p;
  }

The two tests don’t validate the output in any way. Would it be possible to add validation? Perhaps hard to make sure an object is on the finalizer queue… Hmm.

Thanks,
/Staffan


> On 5 maj 2015, at 12:01, Dmitry Samersoff <dmitry.samersoff at oracle.com> wrote:
> 
> Everyone,
> 
> Please review the fix:
> 
> http://cr.openjdk.java.net/~dsamersoff/JDK-8059036/webrev.01/
> 
> heap dcmd outputs the same information as SIGBREAK
> 
> finalizerinfo dcmd outputs a list of all classes in finalization queue
> with count
> 
> -Dmitry
> 
> -- 
> Dmitry Samersoff
> Oracle Java development team, Saint Petersburg, Russia
> * I would love to change the world, but they won't give me the sources.