建站技术入门,重庆大渡口营销型网站建设价格,wordpress去掉rss订阅,淘宝官网首页登录semaphore是一个内置的计数器 每当调用acquire()时#xff0c;内置计数器-1
每当调用release()时#xff0c;内置计数器1 计数器不能小于0#xff0c;当计数器为0时#xff0c;acquire()将阻塞线程直到其他线程调用release()。 来看下面的代码#xff1a; import time
imp… semaphore是一个内置的计数器 每当调用acquire()时内置计数器-1
每当调用release()时内置计数器1 计数器不能小于0当计数器为0时acquire()将阻塞线程直到其他线程调用release()。 来看下面的代码 import time
import threadingdef foo():time.sleep(2) #程序休息2秒print(ok,time.ctime())for i in range(20):t1threading.Thread(targetfoo,args()) #实例化一个线程t1.start() #启动线程 执行结果 ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017
ok Tue Jul 18 20:05:58 2017 可以看到程序会在很短的时间内生成20个线程来打印一句话。 如果在主机执行IO密集型任务的时候再执行这种类型的程序时计算机就有很大可能会宕机。 这时候就可以为这段程序添加一个计数器功能来限制一个时间点内的线程数量。 代码如下 import time
import threadings1threading.Semaphore(5) #添加一个计数器def foo():s1.acquire() #计数器获得锁time.sleep(2) #程序休眠2秒print(ok,time.ctime())s1.release() #计数器释放锁for i in range(20):t1threading.Thread(targetfoo,args()) #创建线程t1.start() #启动线程 执行结果 ok Tue Jul 18 20:04:38 2017
ok Tue Jul 18 20:04:38 2017
ok Tue Jul 18 20:04:38 2017
ok Tue Jul 18 20:04:38 2017
ok Tue Jul 18 20:04:38 2017
ok Tue Jul 18 20:04:40 2017
ok Tue Jul 18 20:04:40 2017
ok Tue Jul 18 20:04:40 2017
ok Tue Jul 18 20:04:40 2017
ok Tue Jul 18 20:04:40 2017
ok Tue Jul 18 20:04:42 2017
ok Tue Jul 18 20:04:42 2017
ok Tue Jul 18 20:04:42 2017
ok Tue Jul 18 20:04:42 2017
ok Tue Jul 18 20:04:42 2017
ok Tue Jul 18 20:04:44 2017
ok Tue Jul 18 20:04:44 2017
ok Tue Jul 18 20:04:44 2017
ok Tue Jul 18 20:04:44 2017
ok Tue Jul 18 20:04:44 2017
