Feature request: singleflight to return refcount vs shared bool

[gleonid]

Background:

We are using singleflight to run expensive procedure that creates a temporary resource (temp file)
Our challenge - we need to determine when it is safe to cleanup this temp resource
Currently Group.Do/DoChan calls only return a shared bool indicator, but they do not surface to caller how many actual caller will be using this result.

Proposal to consider:

Currently implementation maintains "dups int" property for each call, semantically it is almost exactly a "reference counter" except in case of single caller it holds value 0 instead of 1.
I propose, to slightly change signature of Group.Do/DoChan: in addition to "shared bool" also return the actual reference counter (pointer to call.dups ?)

This PR provides an implementation for above
In short it does 2 things:

• defines a refShared type and changes Group.Do signature to use in lace of shared bool
• "refactor Group.Do implement via Group.Dochan call" (commit 4eee079)
  This slightly reduces duplicated code and will prevent a race condition on computation of shared flag. This race condition is introduced by previous item, as calculation of shared bool depends on value call.dups and that value could get changed by caller now.

Note

It might be easier to review this PR on per commit basis

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(6 comments)

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[gleonid]

declining this PR in favor of #9