python threading Future源码解析

1. Future内部还是用了condition这个锁

2. Cancel

# future在执行时，会一直更新这个状态    
def cancel(self):
        """Cancel the future if possible.

        Returns True if the future was cancelled, False otherwise. A future
        cannot be cancelled if it is running or has already completed.
        """
        with self._condition:
            if self._state in [RUNNING, FINISHED]:
                return False

            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
                return True

            self._state = CANCELLED
            self._condition.notify_all()

        self._invoke_callbacks()
        return True

2. result

    def result(self, timeout=None):
        """Return the result of the call that the future represents.

        Args:
            timeout: The number of seconds to wait for the result if the future
                isn't done. If None, then there is no limit on the wait time.

        Returns:
            The result of the call that the future represents.

        Raises:
            CancelledError: If the future was cancelled.
            TimeoutError: If the future didn't finish executing before the given
                timeout.
            Exception: If the call raised then that exception will be raised.
        """
        with self._condition:
            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
                raise CancelledError()
            elif self._state == FINISHED:
                return self.__get_result()

            self._condition.wait(timeout)

            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
                raise CancelledError()
            elif self._state == FINISHED:
                return self.__get_result()
            else:
                raise TimeoutError()

3. set_result

    def set_result(self, result):
        """Sets the return value of work associated with the future.

        Should only be used by Executor implementations and unit tests.
        """
        with self._condition:
            self._result = result
            self._state = FINISHED
            for waiter in self._waiters:
                waiter.add_result(self) #通知主线程
            self._condition.notify_all() # 通知其他使用了condition这个锁的，比如result
        self._invoke_callbacks()