import time
import threading

sem = threading.Semaphore(2)  #限制线程最大数量
def function(c,d):
    with sem:  #锁定线程的最大数量
       print(str(c) +  ' '+ str(d))
       time.sleep(3)
       print('-----------------')

for c in range(1,255):
    ts=threading.Thread(target=function,args=(c,c))
    ts.start()