SickGear/lib/filelock/_api.py

from __future__ import annotations

import contextlib
import logging
import os
import time
import warnings
from abc import ABC, abstractmethod
from threading import Lock
from types import TracebackType
from typing import Any

from ._error import Timeout

_LOGGER = logging.getLogger("filelock")


# This is a helper class which is returned by :meth:`BaseFileLock.acquire` and wraps the lock to make sure __enter__
# is not called twice when entering the with statement. If we would simply return *self*, the lock would be acquired
# again in the *__enter__* method of the BaseFileLock, but not released again automatically. issue #37 (memory leak)
class AcquireReturnProxy:
    """A context aware object that will release the lock file when exiting."""

    def __init__(self, lock: BaseFileLock) -> None:
        self.lock = lock

    def __enter__(self) -> BaseFileLock:
        return self.lock

    def __exit__(
        self,
        exc_type: type[BaseException] | None,  # noqa: U100
        exc_value: BaseException | None,  # noqa: U100
        traceback: TracebackType | None,  # noqa: U100
    ) -> None:
        self.lock.release()


class BaseFileLock(ABC, contextlib.ContextDecorator):
    """Abstract base class for a file lock object."""

    def __init__(self, lock_file: str | os.PathLike[Any], timeout: float = -1) -> None:
        """
        Create a new lock object.

        :param lock_file: path to the file
        :param timeout: default timeout when acquiring the lock, in seconds. It will be used as fallback value in
        the acquire method, if no timeout value (``None``) is given. If you want to disable the timeout, set it
        to a negative value. A timeout of 0 means, that there is exactly one attempt to acquire the file lock.
        """
        # The path to the lock file.
        self._lock_file: str = os.fspath(lock_file)

        # The file descriptor for the *_lock_file* as it is returned by the os.open() function.
        # This file lock is only NOT None, if the object currently holds the lock.
        self._lock_file_fd: int | None = None

        # The default timeout value.
        self._timeout: float = timeout

        # We use this lock primarily for the lock counter.
        self._thread_lock: Lock = Lock()

        # The lock counter is used for implementing the nested locking mechanism. Whenever the lock is acquired, the
        # counter is increased and the lock is only released, when this value is 0 again.
        self._lock_counter: int = 0

    @property
    def lock_file(self) -> str:
        """:return: path to the lock file"""
        return self._lock_file

    @property
    def timeout(self) -> float:
        """
        :return: the default timeout value, in seconds

        .. versionadded:: 2.0.0
        """
        return self._timeout

    @timeout.setter
    def timeout(self, value: float | str) -> None:
        """
        Change the default timeout value.

        :param value: the new value, in seconds
        """
        self._timeout = float(value)

    @abstractmethod
    def _acquire(self) -> None:
        """If the file lock could be acquired, self._lock_file_fd holds the file descriptor of the lock file."""
        raise NotImplementedError

    @abstractmethod
    def _release(self) -> None:
        """Releases the lock and sets self._lock_file_fd to None."""
        raise NotImplementedError

    @property
    def is_locked(self) -> bool:
        """

        :return: A boolean indicating if the lock file is holding the lock currently.

        .. versionchanged:: 2.0.0

            This was previously a method and is now a property.
        """
        return self._lock_file_fd is not None

    def acquire(
        self,
        timeout: float | None = None,
        poll_interval: float = 0.05,
        *,
        poll_intervall: float | None = None,
        blocking: bool = True,
    ) -> AcquireReturnProxy:
        """
        Try to acquire the file lock.

        :param timeout: maximum wait time for acquiring the lock, ``None`` means use the default :attr:`~timeout` is and
         if ``timeout < 0``, there is no timeout and this method will block until the lock could be acquired
        :param poll_interval: interval of trying to acquire the lock file
        :param poll_intervall: deprecated, kept for backwards compatibility, use ``poll_interval`` instead
        :param blocking: defaults to True. If False, function will return immediately if it cannot obtain a lock on the
         first attempt. Otherwise this method will block until the timeout expires or the lock is acquired.
        :raises Timeout: if fails to acquire lock within the timeout period
        :return: a context object that will unlock the file when the context is exited

        .. code-block:: python

            # You can use this method in the context manager (recommended)
            with lock.acquire():
                pass

            # Or use an equivalent try-finally construct:
            lock.acquire()
            try:
                pass
            finally:
                lock.release()

        .. versionchanged:: 2.0.0

            This method returns now a *proxy* object instead of *self*,
            so that it can be used in a with statement without side effects.

        """
        # Use the default timeout, if no timeout is provided.
        if timeout is None:
            timeout = self.timeout

        if poll_intervall is not None:
            msg = "use poll_interval instead of poll_intervall"
            warnings.warn(msg, DeprecationWarning, stacklevel=2)
            poll_interval = poll_intervall

        # Increment the number right at the beginning. We can still undo it, if something fails.
        with self._thread_lock:
            self._lock_counter += 1

        lock_id = id(self)
        lock_filename = self._lock_file
        start_time = time.monotonic()
        try:
            while True:
                with self._thread_lock:
                    if not self.is_locked:
                        _LOGGER.debug("Attempting to acquire lock %s on %s", lock_id, lock_filename)
                        self._acquire()

                if self.is_locked:
                    _LOGGER.debug("Lock %s acquired on %s", lock_id, lock_filename)
                    break
                elif blocking is False:
                    _LOGGER.debug("Failed to immediately acquire lock %s on %s", lock_id, lock_filename)
                    raise Timeout(self._lock_file)
                elif 0 <= timeout < time.monotonic() - start_time:
                    _LOGGER.debug("Timeout on acquiring lock %s on %s", lock_id, lock_filename)
                    raise Timeout(self._lock_file)
                else:
                    msg = "Lock %s not acquired on %s, waiting %s seconds ..."
                    _LOGGER.debug(msg, lock_id, lock_filename, poll_interval)
                    time.sleep(poll_interval)
        except BaseException:  # Something did go wrong, so decrement the counter.
            with self._thread_lock:
                self._lock_counter = max(0, self._lock_counter - 1)
            raise
        return AcquireReturnProxy(lock=self)

    def release(self, force: bool = False) -> None:
        """
        Releases the file lock. Please note, that the lock is only completely released, if the lock counter is 0. Also
        note, that the lock file itself is not automatically deleted.

        :param force: If true, the lock counter is ignored and the lock is released in every case/
        """
        with self._thread_lock:

            if self.is_locked:
                self._lock_counter -= 1

                if self._lock_counter == 0 or force:
                    lock_id, lock_filename = id(self), self._lock_file

                    _LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename)
                    self._release()
                    self._lock_counter = 0
                    _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)

    def __enter__(self) -> BaseFileLock:
        """
        Acquire the lock.

        :return: the lock object
        """
        self.acquire()
        return self

    def __exit__(
        self,
        exc_type: type[BaseException] | None,  # noqa: U100
        exc_value: BaseException | None,  # noqa: U100
        traceback: TracebackType | None,  # noqa: U100
    ) -> None:
        """
        Release the lock.

        :param exc_type: the exception type if raised
        :param exc_value: the exception value if raised
        :param traceback: the exception traceback if raised
        """
        self.release()

    def __del__(self) -> None:
        """Called when the lock object is deleted."""
        self.release(force=True)


__all__ = [
    "BaseFileLock",
    "AcquireReturnProxy",
]