Class Event

python/python3/tornado/locks.py:158–255

An event blocks coroutines until its internal flag is set to True. Similar to `threading.Event`. A coroutine can wait for an event to be set. Once it is set, calls to ``yield event.wait()`` will not block unless the event has been cleared: .. testcode:: import asyncio

class Event(object):
    """An event blocks coroutines until its internal flag is set to True.

    Similar to `threading.Event`.

    A coroutine can wait for an event to be set. Once it is set, calls to
    ``yield event.wait()`` will not block unless the event has been cleared:

    .. testcode::

        import asyncio
        from tornado import gen
        from tornado.locks import Event

        event = Event()

        async def waiter():
            print("Waiting for event")
            await event.wait()
            print("Not waiting this time")
            await event.wait()
            print("Done")

        async def setter():
            print("About to set the event")
            event.set()

        async def runner():
            await gen.multi([waiter(), setter()])

        asyncio.run(runner())

    .. testoutput::

        Waiting for event
        About to set the event
        Not waiting this time
        Done
    """

    def __init__(self) -> None:
        self._value = False
        self._waiters = set()  # type: Set[Future[None]]

    def __repr__(self) -> str:
        return "<%s %s>" % (
            self.__class__.__name__,
            "set" if self.is_set() else "clear",
        )

    def is_set(self) -> bool:
        """Return ``True`` if the internal flag is true."""
        return self._value

    def set(self) -> None:
        """Set the internal flag to ``True``. All waiters are awakened.

        Calling `.wait` once the flag is set will not block.