RFR: 8287073: NPE from CgroupV2Subsystem.getInstance() [v2]

[Ioi Lam]

On Thu, 26 May 2022 09:42:22 GMT, Maxim Kartashev <mkartashev at openjdk.org> wrote:

>> Following the logic from the comment directly above the changed line, since it doesn't matter which controller we pick, pick any available controller instead of the one called "memory" specifically. This way we are guarded against getting `null` as `anyController`, which is being immediately passed down to `CgroupV2Subsystem.getInstance()` that is unprepared to accept `null` values. 
>> 
>> It is also worth noting that the previous checks (such as that at line 89) make sure that there exist at least one controller in the map.
>
> Maxim Kartashev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Removed unnecessary null checks

Changes requested by iklam (Reviewer).

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java line 113:

> 111:             CgroupInfo anyController = infos.values().iterator().next();
> 112:             CgroupSubsystem subsystem = CgroupV2Subsystem.getInstance(anyController);
> 113:             return new CgroupMetrics(subsystem);

Should add `Objects.requireNonNull(anyController)` and `Objects.requireNonNull(subsystem)`.

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java line 116:

> 114:         } else {
> 115:             CgroupV1Subsystem subsystem = CgroupV1Subsystem.getInstance(infos);
> 116:             return new CgroupV1MetricsImpl(subsystem);

This shouldn't be changed because the current implementation of `CgroupV1Subsystem.getInstance(infos)` has a path that returns null.

Maybe that's impossible, because when we call `CgroupV1Subsystem.getInstance`, we must have at least one v1 subsystem in `infos`. However, that's not related to this issue.  Please fix that in a separate RFE. For example, `CgroupV1Subsystem.getInstance(infos)`  can be changed to throw an exception instead if return null.

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PR: https://git.openjdk.java.net/jdk/pull/8803