Understanding Singleflight in Go

I wrote that library originally for dl.google.com: https://go.dev/talks/2013/oscon-dl.slide#1

I then open sourced it in Jan 2013 in what was then named Camlistore (now Perkeep) in https://github.com/perkeep/perkeep/commit/6f9f0bdda9c9c1f147... d

And later I put it in https://pkg.go.dev/github.com/golang/groupcache/singleflight (groupcache was written for dl.google.com)

And a private copy in Go's net package in Jun 2013: https://github.com/golang/go/commit/61d3b2db6292581fc07a3767...

It later moved to golang.org/x/net, and later to the Go standard library (well, internal: https://pkg.go.dev/internal/singleflight)

We now even have a copy with generics in Tailscale's tree at https://pkg.go.dev/tailscale.com/util/singleflight

So many variants of that code :)

"Understanding _using_ singleflight in Go" would be a better title. This generated article doesn't give the reader a real understanding of the implementation and its various tradeoffs that you might care about depending on your workload (e.g. should the first execution to reach a key spawn a goroutine or is that allocation too much)

That being said, singleflight is a fantastic library and pattern that helps so much with p95 latency. It's a little noisy code-wise, but if you use it in the right places the gains are huge.

Also, totally agree with the below comment that recommends janos/singleflight -- start there, but most of the critical projects at my company, AuthZed, have reimplementations with tailored semantics.

This implementation is better than stdlib's implementation in my opinion, since it respects context:

https://github.com/janos/singleflight

First I've heard of this. Lazyweb, why would I use this over sync.Once?