我得到的twisted.internet.error.ReactorNotRestartable错误，当我执行下面的代码：

from time import sleep
from scrapy import signals
from scrapy.crawler import CrawlerProcess
from scrapy.utils.project import get_project_settings
from scrapy.xlib.pydispatch import dispatcher

result = None

def set_result(item):
    result = item

while True:
    process = CrawlerProcess(get_project_settings())
    dispatcher.connect(set_result, signals.item_scraped)

    process.crawl('my_spider')
    process.start()

    if result:
        break
    sleep(3)

第一次起作用，然后出现错误。我process每次都创建变量，这是什么问题？