ConcurrentT.Stage: Why does it not spawn a go routine by itself?

[matthiasgeihs]

@RmbRT During a code review, I saw that method Stage of ConcurrentT is usually run in a go routine:

go ct.Stage(...)
...
ct.Wait(...)

I wonder: Why don't we provide a method that spawns a go routine by default?

ct.StartStage(...)
...
ct.Wait(...)

Is there at all a need for a method that runs in the same routine?

[ggwpez]

We do have code where we already have a go-routine spawned, eg:

go func() {
    // Other Code
    ct.Stage(…)
    // Other Code
}()

It also makes sense to have it when using ctxtest.AssertTerminates.

I think changing it to implicit go-routine spawning would also make the usage less obvious to the user. Since Stage(N) is often used in for loops, a user always has to capture the variables via copy instead of reference since they would otherwise change.
That is only necessary when running in a separate go-routine.

The following code would be wrong without raising much suspicion:

for i := 0;; i++ {
    ct.StartStage(/* use i */)
}

Where as the following pattern is often found in the code:

for i := 0;; i++ {
    i := i
    go ct.Stage(/* use i */)
}