ThreadPoolExecutor 线程池

# coding: utf-8
from concurrent.futures import ThreadPoolExecutor, as_completed
import time
 
 
def spider(page):
    time.sleep(page)
    print(f"crawl task{page} finished")
    return page
 
def main():
    with ThreadPoolExecutor(max_workers=5) as t:
        obj_list = []
        for page in range(1, 5):
            obj = t.submit(spider, page)
            obj_list.append(obj)
 
        for future in as_completed(obj_list):
            data = future.result()
            print(f"main: {data}")

as_completed() 方法是一个生成器，在没有任务完成的时候，会一直阻塞，除非设置了 timeout。

当有某个任务完成的时候，会 yield 这个任务，就能执行 for 循环下面的语句，然后继续阻塞住，循环到所有的任务结束。同时，先完成的任务会先返回给主线程。

from concurrent.futures import ThreadPoolExecutor, wait, FIRST_COMPLETED, ALL_COMPLETED
import time
 
def test(page):
    time.sleep(page)
    print(f"crawl task{page} finished")
    return page
 
with ThreadPoolExecutor(max_workers=5) as t: 
    all_task = [t.submit(test, page) for page in range(1, 5)]
    wait(all_task, return_when=FIRST_COMPLETED)
    print('finished')
    print(wait(all_task, timeout=2.5))