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39 lines
1.1 KiB
Python
39 lines
1.1 KiB
Python
"""
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Context managers, i.e. things you can use with the 'with' statement.
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"""
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from __future__ import absolute_import
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import fcntl
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import os
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from contextlib import contextmanager
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@contextmanager
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def flock(lockfile, shared=False):
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"""Lock a file object using flock(2) for the duration of a 'with' statement.
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If shared is True, use a LOCK_SH lock, otherwise LOCK_EX."""
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fcntl.flock(lockfile, fcntl.LOCK_SH if shared else fcntl.LOCK_EX)
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try:
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yield
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finally:
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fcntl.flock(lockfile, fcntl.LOCK_UN)
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@contextmanager
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def lockfile(filename, shared=False):
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"""Lock a file using flock(2) for the duration of a 'with' statement.
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If shared is True, use a LOCK_SH lock, otherwise LOCK_EX.
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The file is given by name and will be created if it does not exist."""
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if not os.path.exists(filename):
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with open(filename, 'w') as lock:
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lock.write('0')
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# TODO: Can we just open the file for writing, and skip the above check?
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with open(filename, 'r') as lock:
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with flock(lock, shared=shared):
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yield
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