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bpo-40692: Run more test_concurrent_futures tests (GH-20239)

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In the case of multiprocessing.synchronize() being missing, the
test_concurrent_futures test suite now skips only the tests that
require multiprocessing.synchronize().

Validate that multiprocessing.synchronize exists as part of
_check_system_limits(), allowing ProcessPoolExecutor to raise
NotImplementedError during __init__, rather than crashing with
ImportError during __init__ when creating a lock imported from
multiprocessing.synchronize.

Use _check_system_limits() to disable tests of
ProcessPoolExecutor on systems without multiprocessing.synchronize.

Running the test suite without multiprocessing.synchronize reveals
that Lib/compileall.py crashes when it uses a ProcessPoolExecutor.
Therefore, change Lib/compileall.py to call _check_system_limits()
before creating the ProcessPoolExecutor.

Note that both Lib/compileall.py and Lib/test/test_compileall.py
were attempting to sanity-check ProcessPoolExecutor by expecting
ImportError. In multiprocessing.resource_tracker, sem_unlink() is also absent
on platforms where POSIX semaphores aren't available. Avoid using
sem_unlink() if it, too, does not exist.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
This commit is contained in:
Asheesh Laroia 2021-02-07 19:15:51 -08:00 • committed by GitHub
parent 30a8b28396
commit bf2e7e55d7
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6 changed files with 49 additions and 10 deletions
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8
Lib/concurrent/futures/process.py
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@ -532,6 +532,14 @@ def _check_system_limits():
if _system_limited:
raise NotImplementedError(_system_limited)
_system_limits_checked = True
try:
import multiprocessing.synchronize
except ImportError:
_system_limited = (
"This Python build lacks multiprocessing.synchronize, usually due "
"to named semaphores being unavailable on this platform."
)
raise NotImplementedError(_system_limited)
try:
nsems_max = os.sysconf("SC_SEM_NSEMS_MAX")
except (AttributeError, ValueError):