Unexpected ENOTTY in sys::test_termios::test_tcgetattr about nix HOT 3 CLOSED

Is this related to #155?

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I believe this is a separate issue. If I comment out test_wait from #155 this issue still reproduces.

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@carllerche, actually looks like this is sort of related to #155 at least in that it does not reproduce if I set RUST_TEST_THREADS=1. I ran cargo test in a loop for 2 hours with over 11,000 runs before I stopped it. I never saw a failure. Without the environment variable it never ran anywhere near this long without an error.

I don't think this is the same wait problem from #155 - it's a different race against other tests. test_tcgetattr iterates over file descriptors 0..5. What are fds 3, 4 and 5? I believe these fds are being opened and closed by other tests. Here's an example of a possible race:

• Thread 1: runs some other test which opens fd 3 which is not a TTY
• Thread 2: runs test_tcgetattr
• Thread 2: calls tcgetattr on fd 3 which fails with ENOTTY
• Thread 1: closes fd 3
• Thread 2: calls isatty on fd 3 which fails with EBADF
• Thread 2: test_tcgetattr compares the error codes and the assert fails.

Anyway, setting RUST_TEST_THREADS=1 avoids these races.

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