Deprecate lockfile.Locker.RecursiveLock (alternative to #1376)

[mtrmac]

It is not valid as currently implemented, and there is no known user.

Cc: @vrothberg : This was added in #347 , supposedly for the concurrent copy detection.

[vrothberg]

Why not fix it?

I didn't think it entirely through but assume we still need it for the concurrent pull work, don't we?

[mtrmac]

Why not fix it?

Sure, in principle.

I don’t immediately know how to do that

• Go does not provide a recursive locking primitive
• It does not even provide a goroutine ID, which would be necessary for my first guess at how to build one ourselves
• We need to somehow integrate that goroutine with non-recursive uses of the same locks — or maybe we don’t; what does the currently-nonexistent concurrent-pull implementation truly need?

… assume we still need it for the concurrent pull work, don't we?

I don’t know, I haven’t looked into that.

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… and I can’t spend time on this for the next few weeks (months?) at least. In the meantime, I want the problem to be recorded and documented, to prevent accidents.

We can always un-deprecate this after the implementation is fixed.

[mtrmac]

• and we need tests to actually exercise the recursiveness of the locks, contention in recursive situations, and interaction with non-recursive read/write lock owners; IIRC the current ones don’t do (at least some of?) that.

[vrothberg]

We can always un-deprecate this after the implementation is fixed.

Yes, that sounds like a good idea.

LGTM, @nalind are you on board?

[nalind]

It's fine, though the prospect of keeping an API around with known breakage is troubling. If it's only there for a WIP caller that hasn't been merged and isn't actively being worked on, I'm more inclined to just remove it outright and revisit it when it becomes relevant again.

[mtrmac]

I'm more inclined to just remove it outright

Sure: #1376 . I don’t have a strong preference.

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(I have updated this one to deprecate also the callers in C/I/L stores; they seem to be public but can’t actually be directly accessed by external users anyway.)

[rhatdan]

Lets remove it.