Integrated: 8254001: [Metrics] Enhance parsing of cgroup interface files for version detection

[Severin Gehwolf]

On Mon, 23 Nov 2020 15:46:56 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> This is an enhancement which solves two issues:
> 
> 1. Multiple reads of relevant cgroup interface files. Now interface files are only read once per file (just like Hotspot).
> 2. Proxies creation of the impl specific subsystem via `determineType()` as before, but now reads all relevant interface files: `/proc/cgroups`, `/proc/self/mountinfo` and `/proc/self/cgroup`. Once read it passes the parsed information to the impl specific subsystem classes for instantiation. This allows for more flexibility of testing as interface files can be mocked and, thus, more cases can be tested that way without having access to these specific systems. For example, proper regression tests for JDK-8217766 and JDK-8253435 have been added now with this in place.
> 
> * [x] Tested on Linux x86_64 on cgroups v1 and cgroups v2. Container tests pass.

This pull request has now been integrated.

Changeset: a50725db
Author:    Severin Gehwolf <sgehwolf at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/a50725db
Stats:     596 lines in 5 files changed: 323 ins; 144 del; 129 mod

8254001: [Metrics] Enhance parsing of cgroup interface files for version detection

Reviewed-by: hseigel, andrew

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PR: https://git.openjdk.java.net/jdk/pull/1393