python 多线程启动多个摄像头，同时可以暂停摄像头线程

由于比赛需要用到3个摄像头，程序是多线程架构，即主线程开三个子摄像头线程；在主线程（主循环内同时跑另外3个死循环），这样摄像头拍照非常吃cpu为了减少资源和内存cpu忙碌，现在考虑在需要使用摄像头时打开，不使用时暂停相应的摄像头线程；

参考博客：https://blog.csdn.net/weixin_38650871/article/details/117625651?ops_request_misc=&request_id=&biz_id=102&utm_term=python threading暂停线程&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-5-117625651.142^v33^pc_rank_34,185^v2^control&spm=1018.2226.3001.4187

相机线程对象代码的改进：

由threading.Event()此标志位暂停并重新启动线程；具体代码解释见上述参考博客。

import cv2 import threading import time   class Camera:     def __init__(self, src=0, shape=[640, 480]):         self.__flag = threading.Event()         self.__flag.set()  # 设置为True         # 用于停止线程的标识         self.__running = threading.Event()         self.__running.set()  # 将running设置为True          self.src = src         self.stream = cv2.VideoCapture(src)         # self.stream.release()         if self.stream.isOpened():             self.stream.set(cv2.CAP_PROP_FRAME_WIDTH, 640)             self.stream.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)         else:             self.stream = cv2.VideoCapture(self.src   1)             self.stream.set(cv2.CAP_PROP_FRAME_WIDTH, 640)             self.stream.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)         # self.stream.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter::fourcc('M', 'J', 'P', 'G'));         # self.stream.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter_fourcc('Y', 'U', 'Y', 'V'));         self.stopped = False         for _ in range(20):  # warm up the camera             (self.grabbed, self.frame) = self.stream.read()      def start(self):         threading.Thread(target=self.update, args=()).start()      def update(self):         count = 0         while self.__running.isSet():             if self.stream.isOpened():                 self.__flag.wait()  # 为True立即返回， 为False阻塞直到内部标志位置为True后返回                 if self.stopped:                     return                 (self.grabbed, self.frame) = self.stream.read()             else:                 self.__flag.wait()  # 为True立即返回， 为False阻塞直到内部标志位置为True后返回                 print("The video{} is not open!!".format(self.src))                 self.stream = cv2.VideoCapture(self.src   1)                 self.stream.set(cv2.CAP_PROP_FRAME_WIDTH, 640)                 self.stream.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)      def read(self):         return self.frame      def pause(self):         self.__flag.clear()  # 设置为False, 让线程阻塞      def resume(self):         self.__flag.set()  # 设置为True, 阻止线程      def stop(self):          # self.__flag.set()  # 将线程从暂停状态恢复， 若已暂停         self.__running.clear()  # 设置为False         self.stream.release()         self.stopped = True         time.sleep(0.1)   if __name__ == "__main__":     camera = Camera(0)     camera1 = Camera(1)     camera2 = Camera(2)     camera.start()     camera1.start()     camera2.start()     start = end = time.time()     begin = endd = False     try:         while True:             end = time.time()             img = camera.read()             img1 = camera1.read()             img2 = camera2.read()             if end - start > 10 and begin == False:                 camera.pause()                 begin = True             if end - start > 20 and endd == False:                 endd = True                 camera.resume()     finally:         camera.stop()         camera1.stop()         camera2.stop()         # cv2.imshow("img", img)         # cv2.waitKey(1)