`test_profiling` sometimes times out under TSan

[colesbury]

We don't currently run test_profiling in the TSan CI, but the context is that I'm trying to get the entire test suite running under thread sanitizer (TSan).

Some of the tests in test_profiling fail to attach in time when run with thread sanitizer, because the sanitizer makes everything slower. This is especially the case when running tests in parallel with -j.

Here's a example:

ERROR: test_run_failed_script_live (test.test_profiling.test_sampling_profiler.test_live_collector_ui.TestLiveModeErrors.test_run_failed_script_live)
Test that running a failing script exits with clean error.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/sgross/tsan-cpython/Lib/profiling/sampling/cli.py", line 279, in _run_with_sync
    _wait_for_ready_signal(sync_sock, process, _SYNC_TIMEOUT_SEC)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sgross/tsan-cpython/Lib/profiling/sampling/cli.py", line 223, in _wait_for_ready_signal
    raise socket.timeout("timed out")
TimeoutError: timed out

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/sgross/tsan-cpython/Lib/profiling/sampling/cli.py", line 1110, in _handle_live_run
    process = _run_with_sync(cmd, suppress_output=True)
  File "/home/sgross/tsan-cpython/Lib/profiling/sampling/cli.py", line 289, in _run_with_sync
    raise RuntimeError(
        "Process failed to signal readiness within timeout"
    )
RuntimeError: Process failed to signal readiness within timeout

I think the problem is that the the _SYNC_TIMEOUT_SEC of 5 seconds isn't enough in this case:

cpython/Lib/profiling/sampling/cli.py

Line 78 in 4f9a8d0

_SYNC_TIMEOUT_SEC = 5.0

Here are some options to consider:

1. Make _SYNC_TIMEOUT_SEC configurable via a command line option and specify a larger value for the tests (i.e., SHORT_TIMEOUT)
2. Make _SYNC_TIMEOUT_SEC configurable via environment variable
3. Skip these tests under TSan
4. ???

cc @pablogsal

[Yashp002]

I could take a crack at this, I'll update Lib/profiling/sampling/cli.py to accept a timeout argument (likely via a new CLI flag) instead of relying solely on the hardcoded _SYNC_TIMEOUT_SEC.

then i can update the tests in test_sampling_profiler.py to pass test.support.SHORT_TIMEOUT so they adapt to the slower environment of TSan.

If this sounds like the right approach, I'd like to go forward with this?

[colesbury]

Thanks @Yashp002, but I'd like @pablogsal's feedback first on what he thinks is the right approach