tests: use semaphore instead of lock for Endpoint.running

[jcsp]

Problem

Ahem, let's try this again.

#8110 had a spooky failure in test_multi_attach where a call to Endpoint.stop() timed out waiting for a lock, even though we can see an earlier call completing and releasing the lock. I suspect something weird is going on with the way pytest runs tests across processes, or use of asyncio perhaps.

Anyway: the simplest fix is to just use a semaphore instead: if we don't lock we can't deadlock.

Summary of changes

• Make Endpoint.running a semaphore, where we add a unit to its counter when starting the process and atomically decrement it when stopping.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3228 tests run: 3111 passed, 0 failed, 117 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_timeline_size_quota_on_startup: release

Code coverage* (full report)

• functions: 32.4% (6848 of 21165 functions)
• lines: 49.7% (53399 of 107360 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
8cc4c9d at 2024-06-19T15:46:27.823Z :recycle:}