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# filelocker.py - Cross-platform (posix/nt) API for flock-style file locking.
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#                 Requires python 1.5.2 or better.
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"""Cross-platform (posix/nt) API for flock-style file locking.
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Synopsis:
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    import filelocker
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    with filelocker.lock("lockfile", filelocker.LOCK_EX):
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        print "Got it"
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Methods:
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   lock ( file, flags, tries=10 )
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Constants:
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   LOCK_EX
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   LOCK_SH
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   LOCK_NB
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Exceptions:
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    LockException
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Notes:
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For the 'nt' platform, this module requires the Python Extensions for Windows.
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Be aware that this may not work as expected on Windows 95/98/ME.
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History:
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I learned the win32 technique for locking files from sample code
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provided by John Nielsen <nielsenjf@my-deja.com> in the documentation
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that accompanies the win32 modules.
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Author: Jonathan Feinberg <jdf@pobox.com>,
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        Lowell Alleman <lalleman@mfps.com>
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Version: $Id: filelocker.py 5474 2008-05-16 20:53:50Z lowell $
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Modified to work as a contextmanager
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"""
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import os
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from contextlib import contextmanager
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class LockException(Exception):
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    # Error codes:
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    LOCK_FAILED = 1
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# Import modules for each supported platform
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if os.name == 'nt':
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    import win32con
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    import win32file
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    import pywintypes
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    LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
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    LOCK_SH = 0  # the default
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    LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
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    # is there any reason not to reuse the following structure?
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    __overlapped = pywintypes.OVERLAPPED()
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elif os.name == 'posix':
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    import fcntl
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    LOCK_EX = fcntl.LOCK_EX
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    LOCK_SH = fcntl.LOCK_SH
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    LOCK_NB = fcntl.LOCK_NB
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else:
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    raise RuntimeError("FileLocker only defined for nt and posix platforms")
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# --------------------------------------
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# Implementation for NT
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if os.name == 'nt':
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    @contextmanager
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    def lock(filename, flags):
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        file = open(filename, "w+")
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        hfile = win32file._get_osfhandle(file.fileno())
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        try:
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            win32file.LockFileEx(hfile, flags, 0, -0x10000, __overlapped)
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            try:
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                yield
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            finally:
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                file.close()
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        except pywintypes.error, exc_value:
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            # error: (33, 'LockFileEx',
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            #         'The process cannot access the file because another
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            #          process has locked a portion of the file.')
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            file.close()
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            if exc_value[0] == 33:
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                raise LockException(LockException.LOCK_FAILED, exc_value[2])
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            else:
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                # Q:  Are there exceptions/codes we should be dealing with?
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                raise
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# --------------------------------------
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# Implementation for Posix
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elif os.name == 'posix':
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    @contextmanager
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    def lock(filename, flags):
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        file = open(filename, "w+")
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        try:
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            fcntl.flock(file.fileno(), flags)
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            try:
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                yield
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            finally:
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                file.close()
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        except IOError, exc_value:
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            #  IOError: [Errno 11] Resource temporarily unavailable
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            file.close()
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            if exc_value[0] == 11:
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                raise LockException(LockException.LOCK_FAILED, exc_value[1])
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            else:
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                raise