114 lines
3.4 KiB
Python
114 lines
3.4 KiB
Python
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"""
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Portable file locking utilities.
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Based partially on an example by Jonathan Feignberg in the Python
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Cookbook [1] (licensed under the Python Software License) and a ctypes port by
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Anatoly Techtonik for Roundup [2] (license [3]).
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[1] http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/65203
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[2] https://sourceforge.net/p/roundup/code/ci/default/tree/roundup/backends/portalocker.py
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[3] https://sourceforge.net/p/roundup/code/ci/default/tree/COPYING.txt
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Example Usage::
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>>> from django.core.files import locks
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>>> with open('./file', 'wb') as f:
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... locks.lock(f, locks.LOCK_EX)
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... f.write('Django')
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"""
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import os
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__all__ = ('LOCK_EX', 'LOCK_SH', 'LOCK_NB', 'lock', 'unlock')
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def _fd(f):
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"""Get a filedescriptor from something which could be a file or an fd."""
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return f.fileno() if hasattr(f, 'fileno') else f
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if os.name == 'nt':
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import msvcrt
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from ctypes import (sizeof, c_ulong, c_void_p, c_int64,
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Structure, Union, POINTER, windll, byref)
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from ctypes.wintypes import BOOL, DWORD, HANDLE
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LOCK_SH = 0 # the default
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LOCK_NB = 0x1 # LOCKFILE_FAIL_IMMEDIATELY
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LOCK_EX = 0x2 # LOCKFILE_EXCLUSIVE_LOCK
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# --- Adapted from the pyserial project ---
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# detect size of ULONG_PTR
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if sizeof(c_ulong) != sizeof(c_void_p):
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ULONG_PTR = c_int64
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else:
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ULONG_PTR = c_ulong
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PVOID = c_void_p
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# --- Union inside Structure by stackoverflow:3480240 ---
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class _OFFSET(Structure):
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_fields_ = [
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('Offset', DWORD),
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('OffsetHigh', DWORD)]
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class _OFFSET_UNION(Union):
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_anonymous_ = ['_offset']
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_fields_ = [
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('_offset', _OFFSET),
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('Pointer', PVOID)]
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class OVERLAPPED(Structure):
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_anonymous_ = ['_offset_union']
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_fields_ = [
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('Internal', ULONG_PTR),
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('InternalHigh', ULONG_PTR),
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('_offset_union', _OFFSET_UNION),
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('hEvent', HANDLE)]
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LPOVERLAPPED = POINTER(OVERLAPPED)
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# --- Define function prototypes for extra safety ---
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LockFileEx = windll.kernel32.LockFileEx
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LockFileEx.restype = BOOL
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LockFileEx.argtypes = [HANDLE, DWORD, DWORD, DWORD, DWORD, LPOVERLAPPED]
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UnlockFileEx = windll.kernel32.UnlockFileEx
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UnlockFileEx.restype = BOOL
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UnlockFileEx.argtypes = [HANDLE, DWORD, DWORD, DWORD, LPOVERLAPPED]
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def lock(f, flags):
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hfile = msvcrt.get_osfhandle(_fd(f))
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overlapped = OVERLAPPED()
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ret = LockFileEx(hfile, flags, 0, 0, 0xFFFF0000, byref(overlapped))
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return bool(ret)
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def unlock(f):
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hfile = msvcrt.get_osfhandle(_fd(f))
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overlapped = OVERLAPPED()
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ret = UnlockFileEx(hfile, 0, 0, 0xFFFF0000, byref(overlapped))
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return bool(ret)
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else:
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try:
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import fcntl
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LOCK_SH = fcntl.LOCK_SH # shared lock
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LOCK_NB = fcntl.LOCK_NB # non-blocking
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LOCK_EX = fcntl.LOCK_EX
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except (ImportError, AttributeError):
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# File locking is not supported.
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LOCK_EX = LOCK_SH = LOCK_NB = 0
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# Dummy functions that don't do anything.
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def lock(f, flags):
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# File is not locked
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return False
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def unlock(f):
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# File is unlocked
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return True
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else:
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def lock(f, flags):
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ret = fcntl.flock(_fd(f), flags)
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return ret == 0
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def unlock(f):
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ret = fcntl.flock(_fd(f), fcntl.LOCK_UN)
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return ret == 0
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