derp/derphttp: de-flake TestBreakWatcherConnRecv with memnet and synctest #17356
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alexwlchan
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Okay, so this doesn't fully fix it, but the data race now reproduces reliably locally, where previously it was flaky: Progress! |
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Exciting! |
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I think the data race is fixed, so this is ready for review. ✨ |
mikeodr
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Oct 1, 2025
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This is awesome thanks! ✨ |
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Pushed a new commit which uses |
mikeodr
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bradfitz
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bradfitz
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Oct 1, 2025
Yup, that's the plan, but I thought all the indentation changes in the |
Using memnet and synctest removes flakiness caused by real networking and subtle timing differences. Additionally, remove the `t.Logf` call inside the server's shutdown goroutine that was causing a false positive data race detection. The race detector is flagging a double write during this `t.Logf` call. This is a common pattern, noted in golang/go#40343 and elsehwere in this file, where using `t.Logf` after a test has finished can interact poorly with the test runner. This is a long-standing issue which became more common after rewriting this test to use memnet and synctest. Fixed #17355 Signed-off-by: Alex Chan <alexc@tailscale.com>
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TestBreakWatcherConnRecvhas been flaky for a while (#17355), which you can reliably reproduce locally withgolang.org/x/tools/cmd/stress.There's a TODO comment in those tests: "use memnet and synctest". Rewriting the test to use both of those seems to fix the flakiness. I've done 150,000 runs locally with no failures, where previously the tests would fail within a few hundred runs. The test also seems to run a lot faster now. 💪
I recommend reviewing the commits separately – the memnet changes are much easier to read in their own commit. I'll squash them into a single commit when I merge.
Updates #17355