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, 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, e:
          if timeout == 0:
            raise e

          # 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)