Class Event

Lib/threading.py:584–664

Class implementing event objects. Events manage a flag that can be set to true with the set() method and reset to false with the clear() method. The wait() method blocks until the flag is true. The flag is initially false.

class Event:
    """Class implementing event objects.

    Events manage a flag that can be set to true with the set() method and reset
    to false with the clear() method. The wait() method blocks until the flag is
    true.  The flag is initially false.

    """

    # After Tim Peters' event class (without is_posted())

    def __init__(self):
        self._cond = Condition(Lock())
        self._flag = False

    def __repr__(self):
        cls = self.__class__
        status = 'set' if self._flag else 'unset'
        return f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}: {status}>"

    def _at_fork_reinit(self):
        # Private method called by Thread._after_fork()
        self._cond._at_fork_reinit()

    def is_set(self):
        """Return true if and only if the internal flag is true."""
        return self._flag

    def isSet(self):
        """Return true if and only if the internal flag is true.

        This method is deprecated, use is_set() instead.

        """
        import warnings
        warnings.warn('isSet() is deprecated, use is_set() instead',
                      DeprecationWarning, stacklevel=2)
        return self.is_set()

    def set(self):
        """Set the internal flag to true.

        All threads waiting for it to become true are awakened. Threads
        that call wait() once the flag is true will not block at all.

        """
        with self._cond:
            self._flag = True
            self._cond.notify_all()

    def clear(self):
        """Reset the internal flag to false.

        Subsequently, threads calling wait() will block until set() is called to
        set the internal flag to true again.

        """
        with self._cond: