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
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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
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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
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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
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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。
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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
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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：
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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
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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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原文链接：https://blog.csdn.net/qq_31385393/article/details/115873831
