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"""Helper module to factorize the conditional multiprocessing import logic
We use a distinct module to simplify import statements and avoid introducing
circular dependencies (for instance for the assert_spawning name).
"""
import os
import warnings
# Obtain possible configuration from the environment, assuming 1 (on)
# by default, upon 0 set to None. Should instructively fail if some non
# 0/1 value is set.
mp = int(os.environ.get("JOBLIB_MULTIPROCESSING", 1)) or None
if mp:
try:
import _multiprocessing # noqa
import multiprocessing as mp
except ImportError:
mp = None
# 2nd stage: validate that locking is available on the system and
# issue a warning if not
if mp is not None:
try:
# try to create a named semaphore using SemLock to make sure they are
# available on this platform. We use the low level object
# _multiprocessing.SemLock to avoid spawning a resource tracker on
# Unix system or changing the default backend.
import tempfile
from _multiprocessing import SemLock
_rand = tempfile._RandomNameSequence()
for i in range(100):
try:
name = "/joblib-{}-{}".format(os.getpid(), next(_rand))
_sem = SemLock(0, 0, 1, name=name, unlink=True)
del _sem # cleanup
break
except FileExistsError as e: # pragma: no cover
if i >= 99:
raise FileExistsError("cannot find name for semaphore") from e
except (FileExistsError, AttributeError, ImportError, OSError) as e:
mp = None
warnings.warn("%s. joblib will operate in serial mode" % (e,))
# 3rd stage: backward compat for the assert_spawning helper
if mp is not None:
from multiprocessing.context import assert_spawning
else:
assert_spawning = None
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