• 【10.6】线程同步--Semaphore 使用以及源码分析


     1 #!/user/bin/env python
     2 # -*- coding:utf-8 -*-
     3 
     4 # Semaphore 是用于控制进入数量的锁
     5 # 文件、读、写、写一般只是用于一个线程写,读可以允许有多个
     6 
     7 # 做爬虫
     8 import threading
     9 import time
    10 
    11 
    12 class HtmlSpider(threading.Thread):
    13     def __init__(self, url, sem):
    14         super().__init__()
    15         self.url = url
    16         self.sem = sem
    17 
    18     def run(self):
    19         time.sleep(2)
    20         print('got html text success')
    21         self.sem.release()
    22 
    23 
    24 class UrlProducer(threading.Thread):
    25     def __init__(self, sem):
    26         super().__init__()
    27         self.sem = sem
    28 
    29     def run(self):
    30         for i in range(20):
    31             # 每次调用Semaphore的acquire方法,sem = threading.Semaphore(3)设置的次数都会减一
    32             self.sem.acquire()
    33             html_thread = HtmlSpider('http://www.baidu.com/{}'.format(i), self.sem)
    34             html_thread.start()
    35 
    36 
    37 if __name__ == '__main__':
    38     # 一次允许3个并发
    39     sem = threading.Semaphore(3)
    40     url_producer = UrlProducer(sem)
    41     url_producer.start()
    got html text success
    got html text success
    got html text success
    got html text successgot html text success
    
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    got html text success
    

     每2秒弹出一组3个的 ‘got html text success’

    Semaphore底层是用Condition实现的

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  • 原文地址:https://www.cnblogs.com/zydeboke/p/11298706.html
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