RFR: 8275185: Remove dead code and clean up jvmstat LocalVmManager

[Kevin Walls]

On Wed, 13 Oct 2021 04:17:25 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> LocalVmManager and PerfDataFile have APIs that are supposed to look for VMs owned by a specific user. No one uses these APIs, and they don't work anyway.
> 
> The current code is very confusing to look at. Since we're likely to change code in this area for further container support, it's better to clean up the code now.
> 
> - Remove all APIs that take a user name
> - Also removed PerfDataFile.getFile() methods that are unused
> - Cleaned up the code that looks up the hsperfdata_xxx files
>   - Fix comments to explain what's happening
>   - Avoid using Matcher.reset which is not thread-safe
>   - Renamed confusing variables such as `userFilter` to make the code more readable
>   - LocalVmManager.activeVms() probably doesn't need to be synchronized, but I kept it anyway to avoid unnecessary risks.
> 
> Testing with Oracle CI: tiers1-4, plus hs-tier5-rt (which tests containers and have extensive use of the management tools).

Nice cleanup - although was it not better for PerfDataFile.java to "own" the definitions of what a perfdata filename looks like?
That might be what Chris was hinting at.  There isn't really that _much_ flipping between two files. 8-)

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PR: https://git.openjdk.java.net/jdk/pull/5923