Class _ReadWriteLockMeta

src/filelock/_read_write.py:59–96

Metaclass that handles singleton resolution when is_singleton=True. Singleton logic lives here rather than in ReadWriteLock.get_lock so that ``ReadWriteLock(path)`` transparently returns cached instances without a 2-arg ``super()`` call that type checkers cannot verify.

class _ReadWriteLockMeta(type):
    """
    Metaclass that handles singleton resolution when is_singleton=True.

    Singleton logic lives here rather than in ReadWriteLock.get_lock so that ``ReadWriteLock(path)`` transparently
    returns cached instances without a 2-arg ``super()`` call that type checkers cannot verify.

    """

    _instances: WeakValueDictionary[pathlib.Path, ReadWriteLock]
    _instances_lock: threading.Lock

    def __call__(
        cls,
        lock_file: str | os.PathLike[str],
        timeout: float = -1,
        *,
        blocking: bool = True,
        is_singleton: bool = True,
    ) -> ReadWriteLock:
        if not is_singleton:
            return super().__call__(lock_file, timeout, blocking=blocking, is_singleton=is_singleton)

        normalized = pathlib.Path(lock_file).resolve()
        with cls._instances_lock:
            if normalized not in cls._instances:
                instance = super().__call__(lock_file, timeout, blocking=blocking, is_singleton=is_singleton)
                cls._instances[normalized] = instance
            else:
                instance = cls._instances[normalized]

            if instance.timeout != timeout or instance.blocking != blocking:
                msg = (
                    f"Singleton lock created with timeout={instance.timeout}, blocking={instance.blocking},"
                    f" cannot be changed to timeout={timeout}, blocking={blocking}"
                )
                raise ValueError(msg)
            return instance


class ReadWriteLock(metaclass=_ReadWriteLockMeta):