使用“cv2.VideoCapture”（Python OpenCV）时如何正确终止“multiprocessing.Process”？答案

【问题标题】：How to terminate "multiprocessing.Process" correctly when using "cv2.VideoCapture" (Python OpenCV)?使用“cv2.VideoCapture”（Python OpenCV）时如何正确终止“multiprocessing.Process”？
【发布时间】：2018-06-21 08:46:52
【问题描述】：

我对这里发生的事情感到茫然。我正在尝试运行 opencv VideoCapture 进程来读取帧并放入队列以供工作人员处理。

应用程序永远不会完成运行，因为 CameraProcess 实例似乎永远不会终止。经过一番调查，看起来相机在调用#release（）后报告为关闭，但在主进程中被认为是打开的。

我不应该在 Process 中创建 VideoCapture 实例吗？

示例应用程序：

import cv2
from multiprocessing import Process, Event
from time import sleep

class CameraProcess(Process):
    def __init__(self, camera_id, *args, **kwargs):
        super(CameraProcess, self).__init__(*args, **kwargs)
        self.shutdown = Event()

        self.camera = cv2.VideoCapture(camera_id)
        sleep(1)
        print('Camera is opened? {}'.format(self.camera.isOpened()))

    def run(self):
        while not self.shutdown.wait(0.05):
            print('Doing camera stuff')
            sleep(1)

        self.camera.release()
        print('Camera is closed? {}'.format(not self.camera.isOpened()))

try:
    camera = CameraProcess(0)
    camera.start()
    sleep(5)
    camera.shutdown.set()
    sleep(2)
    print('Camera is closed? {}'.format(not camera.camera.isOpened()))
except KeyboardInterrupt:
    pass
finally:
    camera.terminate()

应用程序输出：

相机打开了？真的做相机的东西做相机的东西做相机的东西做相机的东西做相机的东西相机关了？真的相机关了？错误的

环境：

Debian 延伸
Python：3.5.3
cv2：3.4.0

【问题讨论】：

标签： python opencv multiprocessing

【解决方案1】：

奇怪的是，它应该被释放。但是相机资源仍然被占用。可能是一个错误？或者也许它是新事物......

为了正确释放资源，我定义了一个新方法如下。然后就可以了。

import cv2
from multiprocessing import Process, Event
from time import sleep

class CameraProcess(Process):
    def __init__(self, camera_id, *args, **kwargs):
        super(CameraProcess, self).__init__(*args, **kwargs)
        self.shutdown = Event()

        self.camera = cv2.VideoCapture(camera_id)
        print('Camera is opened? {}'.format(self.camera.isOpened()))

    def run(self):
        while not self.shutdown.wait(0.05):
            print('Doing camera stuff')
            sleep(1)
        self.camera.release()
        print('[run   ] Camera is closed? {}'.format(not self.camera.isOpened()))

    ## Defind a new method to release the resourse(again).
    def shutup(self):
        self.shutdown.set()
        if self.camera.isOpened():
            self.camera.release()
        print('[shutup] Camera is closed? {}'.format(not self.camera.isOpened()))

try:
    camera = CameraProcess(0)
    camera.start()
    sleep(5)
    camera.shutup()
    sleep(2)
    print('[main  ] Camera is closed? {}'.format(not camera.camera.isOpened()))
except KeyboardInterrupt:
    pass
finally:
    camera.terminate()

结果现在是OK。

Camera is opened? True
Doing camera stuff
Doing camera stuff
Doing camera stuff
Doing camera stuff
Doing camera stuff
[shutup] Camera is closed? True
[run   ] Camera is closed? True
[main  ] Camera is closed? True

【讨论】：