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51 lines
1.5 KiB
Python
51 lines
1.5 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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import fcntl
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from collections.abc import Iterator
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from contextlib import contextmanager
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from typing import IO, Any
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@contextmanager
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def flock(lockfile: int | IO[Any], shared: bool = False) -> Iterator[None]:
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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: str, shared: bool = False) -> Iterator[None]:
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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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with open(filename, "w") as lock, flock(lock, shared=shared):
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yield
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@contextmanager
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def lockfile_nonblocking(filename: str) -> Iterator[bool]: # nocoverage
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"""Lock a file using flock(2) for the duration of a 'with' statement.
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Doesn't block, yields False immediately if the lock can't be acquired."""
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with open(filename, "w") as f:
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lock_acquired = False
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try:
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fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
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lock_acquired = True
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yield lock_acquired
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except BlockingIOError:
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yield False
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finally:
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if lock_acquired:
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fcntl.flock(f, fcntl.LOCK_UN)
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