| """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 | |