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      1 #!/usr/bin/env python
      2 # Copyright (C) 2010 Gabor Rapcsanyi (rgabor (at] inf.u-szeged.hu), University of Szeged
      3 #
      4 # All rights reserved.
      5 #
      6 # Redistribution and use in source and binary forms, with or without
      7 # modification, are permitted provided that the following conditions
      8 # are met:
      9 # 1. Redistributions of source code must retain the above copyright
     10 #    notice, this list of conditions and the following disclaimer.
     11 # 2. Redistributions in binary form must reproduce the above copyright
     12 #    notice, this list of conditions and the following disclaimer in the
     13 #    documentation and/or other materials provided with the distribution.
     14 #
     15 # THIS SOFTWARE IS PROVIDED BY UNIVERSITY OF SZEGED ``AS IS'' AND ANY
     16 # EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     17 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     18 # PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL UNIVERSITY OF SZEGED OR
     19 # CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
     20 # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     21 # PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
     22 # PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
     23 # OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     24 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     25 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     26 
     27 """This class helps to lock files exclusively across processes."""
     28 
     29 import logging
     30 import os
     31 import sys
     32 import time
     33 
     34 
     35 _log = logging.getLogger("webkitpy.common.system.file_lock")
     36 
     37 
     38 class FileLock(object):
     39 
     40     def __init__(self, lock_file_path, max_wait_time_sec=20):
     41         self._lock_file_path = lock_file_path
     42         self._lock_file_descriptor = None
     43         self._max_wait_time_sec = max_wait_time_sec
     44 
     45     def _create_lock(self):
     46         if sys.platform in ('darwin', 'linux2', 'cygwin'):
     47             import fcntl
     48             fcntl.flock(self._lock_file_descriptor, fcntl.LOCK_EX | fcntl.LOCK_NB)
     49         elif sys.platform == 'win32':
     50             import msvcrt
     51             msvcrt.locking(self._lock_file_descriptor, msvcrt.LK_NBLCK, 32)
     52 
     53     def _remove_lock(self):
     54         if sys.platform in ('darwin', 'linux2', 'cygwin'):
     55             import fcntl
     56             fcntl.flock(self._lock_file_descriptor, fcntl.LOCK_UN)
     57         elif sys.platform == 'win32':
     58             import msvcrt
     59             msvcrt.locking(self._lock_file_descriptor, msvcrt.LK_UNLCK, 32)
     60 
     61     def acquire_lock(self):
     62         self._lock_file_descriptor = os.open(self._lock_file_path, os.O_TRUNC | os.O_CREAT)
     63         start_time = time.time()
     64         while True:
     65             try:
     66                 self._create_lock()
     67                 return True
     68             except IOError:
     69                 if time.time() - start_time > self._max_wait_time_sec:
     70                     _log.debug("File locking failed: %s" % str(sys.exc_info()))
     71                     os.close(self._lock_file_descriptor)
     72                     self._lock_file_descriptor = None
     73                     return False
     74 
     75     def release_lock(self):
     76         try:
     77             if self._lock_file_descriptor:
     78                 self._remove_lock()
     79                 os.close(self._lock_file_descriptor)
     80                 self._lock_file_descriptor = None
     81             os.unlink(self._lock_file_path)
     82         except (IOError, OSError):
     83             _log.debug("Warning in release lock: %s" % str(sys.exc_info()))
     84