locked_file.py 文件源码

def open_and_lock(self, timeout, delay):
            """Open the file and lock it.

            Args:
                timeout: float, How long to try to lock for.
                delay: float, How long to wait between retries

            Raises:
                AlreadyLockedException: if the lock is already acquired.
                IOError: if the open fails.
                CredentialsFileSymbolicLinkError: if the file is a symbolic
                                                  link.
            """
            if self._locked:
                raise AlreadyLockedException('File %s is already locked' %
                                             self._filename)
            start_time = time.time()

            validate_file(self._filename)
            try:
                self._fh = open(self._filename, self._mode)
            except IOError as e:
                # If we can't access with _mode, try _fallback_mode
                # and don't lock.
                if e.errno == errno.EACCES:
                    self._fh = open(self._filename, self._fallback_mode)
                    return

            # We opened in _mode, try to lock the file.
            while True:
                try:
                    hfile = win32file._get_osfhandle(self._fh.fileno())
                    win32file.LockFileEx(
                        hfile,
                        (win32con.LOCKFILE_FAIL_IMMEDIATELY |
                         win32con.LOCKFILE_EXCLUSIVE_LOCK), 0, -0x10000,
                        pywintypes.OVERLAPPED())
                    self._locked = True
                    return
                except pywintypes.error as e:
                    if timeout == 0:
                        raise

                    # If the error is not that the file is already
                    # in use, raise.
                    if e[0] != _Win32Opener.FILE_IN_USE_ERROR:
                        raise

                    # We could not acquire the lock. Try again.
                    if (time.time() - start_time) >= timeout:
                        logger.warn('Could not lock %s in %s seconds' % (
                            self._filename, timeout))
                        if self._fh:
                            self._fh.close()
                        self._fh = open(self._filename, self._fallback_mode)
                        return
                    time.sleep(delay)