信号量

import random
import time
from multiprocessing import Process
from multiprocessing import Semaphore    #信号量类

def ktv(i,sem):
    sem.acquire()
    print('%s走进KTV'%i)
    time.sleep(random.randint(60,120))
    print('%s走出KTV'%i)
    sem.release()

if __name__=='__main__':
    sem = Semaphore(4)
    for i in range(20):
        p=Process(target = ktv,args=(i,sem))
        p.start()