Python多线程编程之threading模块详解

一、介绍

线程是什么？线程有啥用？线程和进程的区别是什么？

线程是操作系统能够进行运算调度的最小单位。被包含在进程中，是进程中的实际运作单位。一条线程指的是进程中一个单一顺序的控制流，一个进程中可以并发多个线程，每条线程并行执行不同的任务。

二、Python如何创建线程2.1 方法一：

创建Thread对象

步骤：

1.目标函数

2.实例化Thread对象

3.调用start()方法

import threading# 目标函数1def fun1(num): for i in range(num):print(’线程1: 第%d次循环:’ % i)# 目标函数2def fun2(lst): for ele in lst:print(’线程2: lst列表中元素 %d’ % ele)def main(): num = 10 # 实例化Thread对象 # target参数一定为一个函数，且不带括号 # args参数为元组类型，参数为一个时一定要加逗号 t1 = threading.Thread(target=fun1, args=(num,)) t2 = threading.Thread(target=fun2, args=([1, 2, 3, 4, 5],)) # 调用start方法 t1.start() t2.start()if __name__ == ’__main__’: main()2.2 方法二：

创建子类继承threading.Thread类

import threadingimport osclass Person(threading.Thread): def run(self):self.sing(5)self.cook() @staticmethod def sing(num):for i in range(num): print(’线程[%d]: The person sing %d song.’ % (os.getpid(), i)) @staticmethod def cook():print(’线程[%d]:The person has cooked breakfast.’ % os.getpid())def main(): p1 = Person() p1.start() p2 = Person() p2.start()if __name__ == ’__main__’: main()三、线程的用法3.1 确定当前的线程

import threadingimport timeimport loggingdef fun1(): print(threading.current_thread().getName(), ’starting’) time.sleep(0.2) print(threading.current_thread().getName(), ’exiting’)def fun2(): # print(threading.current_thread().getName(), ’starting’) # time.sleep(0.3) # print(threading.current_thread().getName(), ’exiting’) logging.debug(’starting’) time.sleep(0.3) logging.debug(’exiting’)logging.basicConfig( level=logging.DEBUG, format=’[%(levelname)s] (%(threadName)-10s) %(message)s’)def main(): t1 = threading.Thread(name=’线程1’, target=fun1) t2 = threading.Thread(name=’线程2’, target=fun2) t1.start() t2.start()if __name__ == ’__main__’: main()3.2 守护线程

区别

普通线程：主线程等待子线程关闭后关闭 守护线程：管你子线程关没关，主线程到时间就关闭

守护线程如何搞

方法1：构造线程时传入dameon=True 方法2：调用setDaemon()方法并提供参数True

import threadingimport timeimport loggingdef daemon(): logging.debug(’starting’) # 添加延时，此时主线程已经退出，exiting不会打印 time.sleep(0.2) logging.debug(’exiting’)def non_daemon(): logging.debug(’starting’) logging.debug(’exiting’)logging.basicConfig( level=logging.DEBUG, format=’[%(levelname)s] (%(threadName)-10s) %(message)s’)def main(): # t1 = threading.Thread(name=’线程1’, target=daemon) # t1.setDaemon(True) t1 = threading.Thread(name=’线程1’, target=daemon, daemon=True) t2 = threading.Thread(name=’线程2’, target=non_daemon) t1.start() t2.start() # 等待守护线程完成工作需要调用join()方法，默认情况join会无限阻塞，可以传入浮点值，表示超时时间 t1.join(0.2) t2.join(0.1)if __name__ == ’__main__’: main()3.3 控制资源访问

目的：

Python线程中资源共享，如果不对资源加上互斥锁，有可能导致数据不准确。

import threadingimport timeg_num = 0def fun1(num): global g_num for i in range(num):g_num += 1 print(’线程1 g_num = %d’ % g_num)def fun2(num): global g_num for i in range(num):g_num += 1 print(’线程2 g_num = %d’ % g_num)def main(): t1 = threading.Thread(target=fun1, args=(1000000,)) t2 = threading.Thread(target=fun1, args=(1000000,)) t1.start() t2.start()if __name__ == ’__main__’: main() time.sleep(1) print(’主线程 g_num = %d’ % g_num)

互斥锁

import threadingimport timeg_num = 0L = threading.Lock()def fun1(num): global g_num L.acquire() for i in range(num):g_num += 1 L.release() print(’线程1 g_num = %d’ % g_num)def fun2(num): global g_num L.acquire() for i in range(num):g_num += 1 L.release() print(’线程2 g_num = %d’ % g_num)def main(): t1 = threading.Thread(target=fun1, args=(1000000,)) t2 = threading.Thread(target=fun1, args=(1000000,)) t1.start() t2.start()if __name__ == ’__main__’: main() time.sleep(1) print(’主线程 g_num = %d’ % g_num)

互斥锁引发的另一个问题：死锁

死锁产生的原理：

import threadingimport timeg_num = 0L1 = threading.Lock()L2 = threading.Lock()def fun1(): L1.acquire(timeout=5) time.sleep(1) L2.acquire() print(’产生死锁，并不会打印信息’) L2.release() L1.release()def fun2(): L2.acquire(timeout=5) time.sleep(1) L1.acquire() print(’产生死锁，并不会打印信息’) L1.release() L2.release()def main(): t1 = threading.Thread(target=fun1) t2 = threading.Thread(target=fun2) t1.start() t2.start()if __name__ == ’__main__’: main() time.sleep(1) print(’主线程 g_num = %d’ % g_num)

如何避免产生死锁：

锁超时操作

import threadingimport timeg_num = 0L1 = threading.Lock()L2 = threading.Lock()def fun1(): L1.acquire() time.sleep(1) L2.acquire(timeout=5) print(’超时异常打印信息1’) L2.release() L1.release()def fun2(): L2.acquire() time.sleep(1) L1.acquire(timeout=5) print(’超时异常打印信息2’) L1.release() L2.release()def main(): t1 = threading.Thread(target=fun1) t2 = threading.Thread(target=fun2) t1.start() t2.start()if __name__ == ’__main__’: main() time.sleep(1) print(’主线程 g_num = %d’ % g_num)

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