make GetUnusedPort concurrency safe

[muff1nman]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Kwok can be used nicely in go test with parallelism. However when running with -race, GetUnusedPort is flagged as a data race. Ancedotally, during our tests we have seen port contention and this might help resolve that.

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @muff1nman. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[wzshiming]

/ok-to-test

[wzshiming]

this function should never be used concurrently.

[muff1nman]

@wzshiming are you saying that I shouldn't be using kwok with https://pkg.go.dev/testing#T.Parallel? I'd find that surprising considering how easy it is to use kwok in testing and with parallelism it makes the tests run very quickly.

[muff1nman]

Actually I think there is more than just GetUnusedPorts that potentially is a problem.

[wzshiming]

Actually I think there is more than just GetUnusedPorts that potentially is a problem.

Yes, I know the kwokctl potentially has this problem, but there's no need for parallelism, right?

[muff1nman]

The difference with t.Parallel is 3.5 minutes vs 23 minutes test runtime. So I'd say its very nice to have.

[wzshiming]

Hello

I would like to verify what you said, and I have not found any way to do it in this codebase, how do you do it exactly, I would like to verify it.

[muff1nman]

I would like to verify what you said

Verify which part exactly?