from threading import Thread,Semaphoreimport timedef func(sem,a,b):    sem.acquire()    time.sleep(0.5)    print(a+b)    sem.release()sem = Semaphore(4)t_lst = []for i in range(10):    t = Thread(target=func,args=(sem,i,i+5))    t.start()    t_lst.append(t)for t in t_lst: t.join()print('主线程')

 

import time,randomfrom threading import Thread,Eventdef connect_db(e):    count = 0    while count < 3:        e.wait(0.5)        if e.is_set() == True:            print('连接至数据库')            break        else:            count += 1            print('第%d次连接失败'%count)    else:        raise TimeoutError('连接超时')def check_web(e):    time.sleep(random.randint(0,3))    e.set()e = Event()t1 = Thread(target=connect_db,args=(e,))t2 = Thread(target=check_web,args=(e,))t1.start()t2.start()