RFR(S): 8168305 GC.class_stats should not require -XX:+UnlockDiagnosticVMOptions

[David Holmes]

On 27/10/2016 6:36 PM, Staffan Larsen wrote:
> All,
>
> Please review this small patch to remove the requirement -XX:+UnlockDiagnosticVMOptions when running the GC.class_stats diagnostic command. Diagnostic commands are used for diagnosing problems and should not require restarting the JVM with a different command line flag if this can be avoided.

Right - it doesn't make sense to have to use UnlockDiagnosticVMOptions 
to run any diagnostic Dcmd. Otherwise it should be a requirement for all.

> While fixing this I also noticed that VM.print_touched_methods said it required -XX:+UnlockDiagnosticVMOptions, while what it really required was -XX:+LogTouchedMethods (which in turn requires -XX:+UnlockDiagnosticVMOptions) so I changed the error message here. In this case I think it is ok to require a special command line flag since collecting the information comes with an overhead.

The only reason a Dcmd should require a specific VM option is if the 
Dcmd will not be able to function unless the VM was started with that 
option - IMHO :) Is that the case for LogTouchedMethods?

Thanks,
David

> I have verified the fix manually and by running these tests: hotspot/test/runtime/CommandLine/PrintTouchedMethods.java hotspot/test/serviceability/sa/TestInstanceKlassSize.java hotspot/test/serviceability/sa/TestInstanceKlassSizeForInterface.java
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8168305
> webrev: http://cr.openjdk.java.net/~sla/8168305/webrev.01/
>
> Thanks,
> /Staffan
>