Semaphore semaphore is a variable that controls access to a public resource or critical section. Semaphore maintains a counter, specify the number of threads that can simultaneously access a resource or enter the critical region. The following article is mainly to introduce the use of thread on Python3.X semaphore, a friend in need can refer to learn, let's look at it.
Foreword
Python recent study, found that basic knowledge about the thread semaphore, in-depth understanding of python thread will be of great help. Therefore, this article will introduce you Python3.X thread semaphore use the following word does not say, take a look at the detailed description together:
Method Example
Threads, semaphores are used primarily to maintain a limited resource, so that the thread uses the resource at a certain time only the designated number
# -*- 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()
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summary
That's all for this article, I hope the content of this paper, we study or work can bring some help
