【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()
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每2秒弹出一组3个的 ‘got html text success’
Semaphore底层是用Condition实现的
