1#!/usr/bin/env python
2# Copyright (C) 2010 Gabor Rapcsanyi (rgabor@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
29import logging
30import os
31import sys
32import time
33
34
35_log = logging.getLogger("webkitpy.common.system.file_lock")
36
37
38class 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