Replace usage of sync/atomic with uber-go/atomic

[jvrplmlmn]

What this PR does: Replaces all direct usages of sync/atomic with go.uber.org/atomic. That way we ensure that all access to variables that have atomic access is in fact always atomic.

Which issue(s) this PR fixes:
Fixes #2923

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[jvrplmlmn]

@pracucci would you mind reviewing this PR?

[pstibrany]

Thanks for doing this! Would you mind looking at https://github.com/grafana/loki repository as well? Some of the code there is copied from Cortex.

[pracucci]

Fantastic job, well done, thanks! ❤️ 👏

@pstibrany Could you review this PR too, so we can get this merged?

[pstibrany]

LGTM. Thanks a lot!

There are some places where we should remove pointers to atomic types, and use them directly:

• pkg/ingester/ingester_v2.go:57
• pkg/querier/frontend/frontend.go:70
• pkg/querier/frontend/worker_frontend_manager.go:37
• pkg/ring/lifecycler.go:125
• pkg/ring/kv/multi.go:92
• pkg/ring/kv/multi.go:98

Do you think we can get it done as part of this PR?

[jvrplmlmn]

Hey @pstibrany, I would rather have this merged as it is and send those additional changes in a subsequent PR if that is okay with you.

[pstibrany]

Hey @pstibrany, I would rather have this merged as it is and send those additional changes in a subsequent PR if that is okay with you.

Sounds good to me.

[pstibrany]

Thanks for your PR and looking forward to the next one ;-)