#3122: Using of Synced

[levBagryansky]

Closes #3122

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PR-Codex overview

This PR introduces a new Synced scalar to synchronize access in DcsWithRuntime class.

Detailed summary

• Added Synced scalar import
• Wrapped Sticky scalar in Synced scalar for synchronization

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[levBagryansky]

@yegor256 this case is similar to #3114. This bug is too difficult to show in tests, because this is Singleton + Sticky. However it has obvious cause: There are static Sticky objects that can be used by multiple threads. I have a test that fails if it was firtst, but the problem is that we cannot "reset" state of singleton to initial, and previous influence.

[levBagryansky]

@yegor256 Let's just merge this fix

[yegor256]

@rultor merge

[rultor]

@rultor merge

@yegor256 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@yegor256 Done! FYI, the full log is here (took me 18min)