python的线程池使用

from concurrent.futures import ThreadPoolExecutor
import time


def say_hello(a, s):
    print("hello: "+a)
    print(s)
    time.sleep(4)
    return {"code": 111}


def main():
    seed=["a","b","c", "d"]
    start2=time.time()
    future = {}
    # 创建包含3个线程的线程池
    executor = ThreadPoolExecutor(3)
    for each in seed:
        # 提交任务到线程池
        a = executor.submit(say_hello, each, 4)
        # 保存提交后返回的对象用来查询结果(A Future representing the given call)
        future[each] = a
    # shutdown用来保证不会在向线程池中新增任务,其内参数为False表示不会等待线程池内任务结束,直接返回(常用于不需要返回结果时),参数为True时(默认为True),会等待线程池内任务执行完毕才会继续向下走
    executor.shutdown(False)
    # 当使用future["a"].result()时,无论shutdown内参数是True还是False,都会阻塞至直到该任务执行完.
    # result()内的数字为超时时间,单位是s,默认值为None,无超时时间
    print(future["a"].result(5))
    end2=time.time()
    print("time2: "+str(end2-start2))
    return


if __name__ == '__main__':
    main()