Avoid buffer race conditions in CGroups

[RussKie]

Fixes #5114

Microsoft Reviewers: Open in CodeFlow

[mobratil]

@RussKie can we use object pool instead of having it thread local?
I'm a bit worried that if the methods are invoked each time from a different thread it will create a new buffer every time.
Having an object pool instead will reuse the same buffer. The new buffer will be created only when there' no buffer in the pool which will rarely happen (only in case of contention).

[RussKie]

@mobratil what you think of this?

[mobratil]

@RussKie Now it looks good, thanks