text: """
  owtf.lib.filelock
  ~~~~~~~~~~~~~~~~~
  
  Implementation of a simple cross-platform file locking mechanism.
  This is a modified version of code retrieved on 2013-01-01 from
  http://www.evanfosmark.com/2009/01/cross-platform-file-locking-support-in-python.
  The original code was released under the BSD License, as is this modified version.
  Modifications in this version:
   - Tweak docstrings for sphinx.
   - Accept an absolute path for the protected file (instead of a file name relative to cwd).
   - Allow timeout to be None.
   - Fixed a bug that caused the original code to be NON-threadsafe when the same FileLock instance was
     shared by multiple threads in one process.
     (The original was safe for multiple processes, but not multiple threads in a single process.
     This version is safe for both cases.)
   - Added ``purge()`` function.
   - Added ``available()`` function.
   - Expanded API to mimic ``threading.Lock interface``:
     - ``__enter__`` always calls ``acquire()``, and therefore blocks if ``acquire()`` was called previously.
     - ``__exit__`` always calls ``release()``.  It is therefore a bug to call ``release()`` from within a
     context manager.
     - Added ``locked()`` function.
     - Added blocking parameter to ``acquire()`` method
  
  # taken from https://github.com/ilastik/lazyflow/blob/master/lazyflow/utility/fileLock.py
  # original version from http://www.evanfosmark.com/2009/01/cross-platform-file-locking-support-in-python/
  """
  
  import os
  import sys
  import time
  import errno
  
  
  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.
      """
  
      class FileLockException(Exception):
          pass
  
      def __init__(self, protected_file_path, timeout=None, delay=1, lock_file_contents=None):
          """ Prepare the file locker. Specify the file to lock and optionally
              the maximum timeout and the delay between each attempt to lock.
          """
          self.is_locked = False
          self.lockfile = protected_file_path + ".lock"
          self.timeout = timeout
          self.delay = delay
          self._lock_file_contents = lock_file_contents
          if self._lock_file_contents is None:
              self._lock_file_contents = "Owning process args:\n"
              for arg in sys.argv:
                  self._lock_file_contents += arg + "\n"
  
      def locked(self):
          """Returns True iff the file is owned by THIS FileLock instance.
          (Even if this returns false, the file could be owned by another FileLock instance,
          possibly in a different thread or process).
  
          :return: True if file owned by Filelock instance
          :rtype: `bool`
          """
          return self.is_locked
  
      def available(self):
          """Returns True iff the file is currently available to be locked.
  
          :return: True if lockfile is available
          :rtype: `bool`
          """
          return not os.path.exists(self.lockfile)
  
      def acquire(self, blocking=True):
          """Acquire the lock, if possible. If the lock is in use, and `blocking` is False, return False.
              Otherwise, check again every `self.delay` seconds until it either gets the lock or
              exceeds `timeout` number of seconds, in which case it raises an exception.
  
          :param blocking: File blocked or not
          :type blocking: `bool`
          :return: True if lock is acquired, else False
          :rtype: `bool`
          """
  
          start_time = time.time()
          while True:
              try:
                  # Attempt to create the lockfile.
                  # These flags cause os.open to raise an OSError if the file already exists.
                  fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
                  with os.fdopen(fd, 'a') as f:
                      # Print some info about the current process as debug info for anyone who bothers to look.
                      f.write(self._lock_file_contents)
                  break
              except OSError as e:
                  if e.errno != errno.EEXIST:
                      raise
                  if self.timeout is not None and (time.time() - start_time) >= self.timeout:
                      raise FileLock.FileLockException("Timeout occurred for lock '%s'." % self.lockfile)
                  if not blocking:
                      return False
                  time.sleep(self.delay)
          self.is_locked = True
          return 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.
  
          :return: None
          :rtype: None
          """
          self.is_locked = False
          os.unlink(self.lockfile)
  
      def __enter__(self):
          """ Activated when used in the with statement.
              Should automatically acquire a lock to be used in the with block.
          """
          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.
          """
          self.release()
  
      def __del__(self):
          """ Make sure this ``FileLock`` instance doesn't leave a .lock file
              lying around.
          """
          if self.is_locked:
              self.release()
  
      def purge(self):
          """
          For debug purposes only.  Removes the lock file from the hard disk.
          """
          if os.path.exists(self.lockfile):
              self.release()
              return True
          return False
  