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50 lines
1.6 KiB
50 lines
1.6 KiB
"""Helper module to factorize the conditional multiprocessing import logic
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We use a distinct module to simplify import statements and avoid introducing
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circular dependencies (for instance for the assert_spawning name).
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"""
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import os
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import sys
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import warnings
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# Obtain possible configuration from the environment, assuming 1 (on)
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# by default, upon 0 set to None. Should instructively fail if some non
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# 0/1 value is set.
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mp = int(os.environ.get('JOBLIB_MULTIPROCESSING', 1)) or None
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if mp:
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try:
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import multiprocessing as mp
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except ImportError:
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mp = None
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# 2nd stage: validate that locking is available on the system and
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# issue a warning if not
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if mp is not None:
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try:
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# Use the spawn context
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if sys.version_info < (3, 3):
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Semaphore = mp.Semaphore
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else:
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# Using mp.Semaphore has a border effect and set the default
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# backend for multiprocessing. To avoid that, we use the 'spawn'
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# context which is available on all supported platforms.
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ctx = mp.get_context('spawn')
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Semaphore = ctx.Semaphore
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_sem = Semaphore()
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del _sem # cleanup
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except (ImportError, OSError) as e:
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mp = None
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warnings.warn('%s. joblib will operate in serial mode' % (e,))
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# 3rd stage: backward compat for the assert_spawning helper
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if mp is not None:
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try:
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# Python 3.4+
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from multiprocessing.context import assert_spawning
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except ImportError:
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from multiprocessing.forking import assert_spawning
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else:
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assert_spawning = None
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