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- # mypy: allow-untyped-defs
- import os
- import time
- import warnings
- class FileBaton:
- """A primitive, file-based synchronization utility."""
- def __init__(self, lock_file_path, wait_seconds=0.1, warn_after_seconds=None):
- """
- Create a new :class:`FileBaton`.
- Args:
- lock_file_path: The path to the file used for locking.
- wait_seconds: The seconds to periodically sleep (spin) when
- calling ``wait()``.
- warn_after_seconds: The seconds to wait before showing
- lock file path to warn existing lock file.
- """
- self.lock_file_path = lock_file_path
- self.wait_seconds = wait_seconds
- self.fd = None
- self.warn_after_seconds = warn_after_seconds
- def try_acquire(self):
- """
- Try to atomically create a file under exclusive access.
- Returns:
- True if the file could be created, else False.
- """
- try:
- self.fd = os.open(self.lock_file_path, os.O_CREAT | os.O_EXCL)
- return True
- except FileExistsError:
- return False
- def wait(self):
- """
- Periodically sleeps for a certain amount until the baton is released.
- The amount of time slept depends on the ``wait_seconds`` parameter
- passed to the constructor.
- """
- has_warned = False
- start_time = time.time()
- while os.path.exists(self.lock_file_path):
- time.sleep(self.wait_seconds)
- if self.warn_after_seconds is not None:
- if time.time() - start_time > self.warn_after_seconds and not has_warned:
- warnings.warn(f'Waited on lock file "{self.lock_file_path}" for '
- f'{self.warn_after_seconds} seconds.')
- has_warned = True
- def release(self):
- """Release the baton and removes its file."""
- if self.fd is not None:
- os.close(self.fd)
- os.remove(self.lock_file_path)
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