| # Copyright (c) 2009, Evan Fosmark |
| # All rights reserved. |
| # |
| # Redistribution and use in source and binary forms, with or without |
| # modification, are permitted provided that the following conditions are met: |
| # * Redistributions of source code must retain the above copyright |
| # notice, this list of conditions and the following disclaimer. |
| # * Redistributions in binary form must reproduce the above copyright |
| # notice, this list of conditions and the following disclaimer in the |
| # documentation and/or other materials provided with the distribution. |
| # * Neither the name of the <organization> nor the |
| # names of its contributors may be used to endorse or promote products |
| # derived from this software without specific prior written permission. |
| # |
| # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| # ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY |
| # DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
| # (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND |
| # ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
| # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| import os |
| import time |
| import errno |
| |
| |
| class FileLockException(Exception): |
| pass |
| |
| |
| class FileLock(object): |
| """A file locking mechanism that has context-manager support so |
| you can use it in a with statement. This should be relatively cross |
| compatible as it doesn't rely on msvcrt or fcntl for the locking. |
| """ |
| |
| def __init__(self, file_name, timeout=10, delay=0.05): |
| """Prepare the file locker. Specify the file to lock and optionally |
| the maximum timeout and the delay between each attempt to lock. |
| """ |
| if timeout is not None and delay is None: |
| raise ValueError( |
| "If timeout is not None, then delay must not be None." |
| ) |
| self.is_locked = False |
| self.lockfile = os.path.join(os.getcwd(), "%s.lock" % file_name) |
| self.file_name = file_name |
| self.timeout = timeout |
| self.delay = delay |
| |
| def acquire(self): |
| """Acquire the lock, if possible. If the lock is in use, it check again |
| every `wait` seconds. It does this until it either gets the lock or |
| exceeds `timeout` number of seconds, in which case it throws |
| an exception. |
| """ |
| start_time = time.time() |
| while True: |
| try: |
| self.fd = os.open( |
| self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR |
| ) |
| self.is_locked = True # moved to ensure tag only when locked |
| break |
| except OSError as e: |
| if e.errno != errno.EEXIST: |
| raise |
| if self.timeout is None: |
| raise FileLockException( |
| "Could not acquire lock on {}".format(self.file_name) |
| ) |
| if (time.time() - start_time) >= self.timeout: |
| raise FileLockException("Timeout occured.") |
| time.sleep(self.delay) |
| |
| # self.is_locked = True |
| |
| def release(self): |
| """Get rid of the lock by deleting the lockfile. |
| When working in a `with` statement, this gets automatically |
| called at the end. |
| """ |
| if self.is_locked: |
| os.close(self.fd) |
| os.unlink(self.lockfile) |
| self.is_locked = False |
| |
| def __enter__(self): |
| """Activated when used in the with statement. |
| Should automatically acquire a lock to be used in the with block. |
| """ |
| if not self.is_locked: |
| self.acquire() |
| return self |
| |
| def __exit__(self, type, value, traceback): |
| """Activated at the end of the with statement. |
| It automatically releases the lock if it isn't locked. |
| """ |
| if self.is_locked: |
| self.release() |
| |
| def __del__(self): |
| """Make sure that the FileLock instance doesn't leave a lockfile |
| lying around. |
| """ |
| self.release() |