def spawn(self, func, *args, **kwargs):
        self.used = True
        self.counter += 1
        try:
            gt = self.pool.spawn(func, *args, **kwargs)
            self.waiters.put(gt)
        except:
            self.counter -= 1
            raise
Run `func` in its own GreenThread
dataset/ETHPy150Open veegee/guv/guv/greenpool.py/GreenPile.spawn