Python3.X 线程中信号量的使用方法示例

前言

最近在学习python，发现了解线程信号量的基础知识，对深入理解python的线程会大有帮助。所以本文将给大家介绍Python3.X线程中信号量的使用方法，下面话不多说，来一起看看详细的介绍：

方法示例

线程中，信号量主要是用来维持有限的资源，使得在一定时间使用该资源的线程只有指定的数量

# -*- coding:utf-8 -*-
""" Created by FizLin on 2017/07/23/-下午10:59
mail: https://github.com/Fiz1994
信号量

maxconnections = 5
...
pool_sema = BoundedSemaphore(value=maxconnections)
Once spawned, worker threads call the semaphore's acquire and release methods when they need to connect to the server:

pool_sema.acquire()
conn = connectdb()
... use connection ...
conn.close()
pool_sema.release()

"""
import threading
import time
import random

sites = ["https://www.baidu.com/", "https://github.com/Fiz1994", "https://stackoverflow.com/",
  "https://www.sogou.com/",
  "http://english.sogou.com/?b_o_e=1&ie=utf8&fr=common_index_nav&query="] * 20
sites_index = 0
maxconnections = 2
pool_sema = threading.BoundedSemaphore(value=maxconnections)

def test():
with pool_sema:
 global sites_index, sites
 url = str(sites[sites_index])
 k = random.randint(10, 20)
 print("爬去： " + url + " 需要时间 : " + str(k))
 sites_index += 1
 # print(url)
 time.sleep(k)
 print('退出 ', url)

for i in range(100):
threading.Thread(target=test).start()

可以发现该程序中，永远只有2个爬虫是处于活动状态

来源：https://segmentfault.com/a/1190000010314270