一、介紹

線程是什么？線程有啥用？線程和進程的區別是什么？

線程是操作系統能夠進行運算調度的最小單位。被包含在進程中，是進程中的實際運作單位。一條線程指的是進程中一個單一順序的控制流，一個進程中可以并發多個線程，每條線程并行執行不同的任務。

二、Python如何創建線程2.1 方法一：

創建Thread對象

步驟：

1.目標函數

2.實例化Thread對象

3.調用start()方法

import threading# 目標函數1def fun1(num): for i in range(num):print(’線程1: 第%d次循環:’ % i)# 目標函數2def fun2(lst): for ele in lst:print(’線程2: lst列表中元素 %d’ % ele)def main(): num = 10 # 實例化Thread對象 # target參數一定為一個函數，且不帶括號 # args參數為元組類型，參數為一個時一定要加逗號 t1 = threading.Thread(target=fun1, args=(num,)) t2 = threading.Thread(target=fun2, args=([1, 2, 3, 4, 5],)) # 調用start方法 t1.start() t2.start()if __name__ == ’__main__’: main()2.2 方法二：

創建子類繼承threading.Thread類

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

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=’線程1’, target=fun1) t2 = threading.Thread(name=’線程2’, target=fun2) t1.start() t2.start()if __name__ == ’__main__’: main()3.2 守護線程

區別

普通線程：主線程等待子線程關閉后關閉 守護線程：管你子線程關沒關，主線程到時間就關閉

守護線程如何搞

方法1：構造線程時傳入dameon=True 方法2：調用setDaemon()方法并提供參數True

import threadingimport timeimport loggingdef daemon(): logging.debug(’starting’) # 添加延時，此時主線程已經退出，exiting不會打印 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=’線程1’, target=daemon) # t1.setDaemon(True) t1 = threading.Thread(name=’線程1’, target=daemon, daemon=True) t2 = threading.Thread(name=’線程2’, target=non_daemon) t1.start() t2.start() # 等待守護線程完成工作需要調用join()方法，默認情況join會無限阻塞，可以傳入浮點值，表示超時時間 t1.join(0.2) t2.join(0.1)if __name__ == ’__main__’: main()3.3 控制資源訪問

目的：

Python線程中資源共享，如果不對資源加上互斥鎖，有可能導致數據不準確。

import threadingimport timeg_num = 0def fun1(num): global g_num for i in range(num):g_num += 1 print(’線程1 g_num = %d’ % g_num)def fun2(num): global g_num for i in range(num):g_num += 1 print(’線程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(’主線程 g_num = %d’ % g_num)

互斥鎖

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(’線程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(’線程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(’主線程 g_num = %d’ % g_num)

互斥鎖引發的另一個問題：死鎖

死鎖產生的原理：

import threadingimport timeg_num = 0L1 = threading.Lock()L2 = threading.Lock()def fun1(): L1.acquire(timeout=5) time.sleep(1) L2.acquire() print(’產生死鎖，并不會打印信息’) L2.release() L1.release()def fun2(): L2.acquire(timeout=5) time.sleep(1) L1.acquire() print(’產生死鎖，并不會打印信息’) 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(’主線程 g_num = %d’ % g_num)

如何避免產生死鎖：

鎖超時操作

import threadingimport timeg_num = 0L1 = threading.Lock()L2 = threading.Lock()def fun1(): L1.acquire() time.sleep(1) L2.acquire(timeout=5) print(’超時異常打印信息1’) L2.release() L1.release()def fun2(): L2.acquire() time.sleep(1) L1.acquire(timeout=5) print(’超時異常打印信息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(’主線程 g_num = %d’ % g_num)

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