from concurrent.futures import ThreadPoolExecutor,ProcessPoolExecutor
import time

def func(i):
    print('star', i)
    time.sleep(2)
    return f'over,{i}'
def cb(res_obj):
    print('callback=====>',res_obj)     #callback=====> <Future at 0x21d7eb8 state=finished returned str>
    print('ccc===>',res_obj.result())   #ccc===> over,0
pool=ThreadPoolExecutor(3)      #(os.cpu_count() or 1) * 5，默认为当前CPU个数的5倍
#pool=ProcessPoolExecutor()      #os.cpu_count() or 1  ,默认为当前CPU的个数

for i in range(1):
    res=pool.submit(func, i)
    print(res)                  #<Future at 0x21d7eb8 state=running>
    res.add_done_callback(cb)   
    #pool.submit(func,i).add_done_callback(cb)