def scale_in(self, blocks):
to_kill = self.blocks[:blocks]<EOL>if self.provider:<EOL><INDENT>r = self.provider.cancel(to_kill)<EOL><DEDENT>return r<EOL>
Scale in the number of active blocks by specified amount.

        The scale in method here is very rude. It doesn't give the workers
        the opportunity to finish current tasks or cleanup. This is tracked
        in issue #530

        Raises:
             NotImplementedError