proposal: testing: add TB.SetGOMAXPROCS

[sivchari]

I propose adding a SetGOMAXPROCS. This idea is inspired by TB.Setenv.

As seen Go source codes, too, if it sets GOMAXPROCS and it unsets this value after cleanup, we must write the following ways.

defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(n))

prev := runtime.GOMAXPROCS(n)
defer runtime.GOMAXPROCS(prev)

The writing style is general, if you know Go specification. But I think we can provide better way to achieve.

I submitted a CL. If this CL isn't been necessary, I don't mind to close it. Thanks.

[earthboundkid]

Does this come up very often? You can also define a third party helper like

func MaxProcs(t testing.TB, n int) {
  prev := runtime.GOMAXPROCS(n)
  t.Cleanup(func() { runtime.GOMAXPROCS(prev) })
}

// in a test
testhelpers.MaxProcs(t, 1)

[gopherbot]

Change https://go.dev/cl/519235 mentions this issue: testing: add TB.SetGOMAXPROCS function

[ianlancetaylor]

That CL should not have been committed. My mistake. Sent a revert.

[gopherbot]

Change https://go.dev/cl/573516 mentions this issue: Revert "testing: add TB.SetGOMAXPROCS function"

[sivchari]

@earthboundkid @ianlancetaylor

I thank you for working. I want to discuss whether this new API is necessary.
When the time comes to review this proposal, please discuss this with me.
Thanks again.