使函数线程安全 [英] Make a function thread safe

问题描述

我试图理解为什么某些函数在 python 中线程失败.例如，我正在尝试使用 VideoCapture 从网络摄像头抓取图像.这个例子工作正常:

from VideoCapture 导入设备凸轮 = 设备()cam.saveSnapshot('image.jpg')

但是当我把它放在一个线程上时，我得到了一个错误.

导入线程从 VideoCapture 导入设备定义抓取():凸轮 = 设备()cam.saveSnapshot('image.jpg')thr = threading.Thread(target=grab)thr.start()thr.join()

<块引用>

文件C:\ProgramFiles\Python36\lib\site-packages\VideoCapture__init__.py"，第 60 行，在初始化self.dev = vidcap.new_Dev(devnum, showVideoWindow) vidcap.Error: 创建过滤器图失败.

根据这个参考，这个函数不是线程安全的.那么是否有任何解决方法可以绕过类似的问题?我尝试使用 threading.lock 但得到了同样的错误.如果我需要更改代码，我应该检查哪个部分?

解决方案

我找不到直接的方法来修复它，但是在线程中导入模块修复了这个问题，我不确定这是否适用于其他模块.

导入线程定义抓取():从 VideoCapture 导入设备凸轮 = 设备()cam.saveSnapshot('image.jpg')德尔卡姆thr = threading.Thread(target=grab)thr.start()thr.join()

I'm trying to understand why some functions fail with threading in python. For example, I'm trying to use VideoCapture to grab an image from a webcam. This example works fine:

from VideoCapture import Device

cam = Device()
cam.saveSnapshot('image.jpg')

But when I put it on a thread I get an error.

import threading
from VideoCapture import Device

def grab():
    cam = Device()
    cam.saveSnapshot('image.jpg')

thr = threading.Thread(target=grab)
thr.start()
thr.join()

File "C:\Program Files\Python36\lib\site-packages\VideoCapture__init__.py", line 60, in init self.dev = vidcap.new_Dev(devnum, showVideoWindow) vidcap.Error: Creation of the filter graph failed.

According to this reference, this function is not thread-safe. So is there any workaround to bypass similar issues like this? I tried to use threading.lock but got the same error. If I need to change the code, which part should I check?

解决方案

I couldn't find a direct way to fix it, but importing the module inside the thread fixed that, I'm not sure if this applies to other modules.

import threading

def grab():
    from VideoCapture import Device
    cam = Device()
    cam.saveSnapshot('image.jpg')
    del cam
thr = threading.Thread(target=grab)
thr.start()
thr.join()

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