Raspberry Pi cv2.VideoCapture stuck at the second time init with same id

user_5530315 0
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I'm facing problem when build my source code to Raspberry Pi.

OpenCV can't init new instance and stuck at step call cv2.VideoCapture.

Here is my source code:

import threading
import time
import cv2

CAPTURE_HZ = 30.0

class Person(object):
    def __init__(self, name, id):
        self._camera = cv2.VideoCapture(id)
        print("Debug")
        self.name = name
        self._capture_frame = None
        # Use a lock to prevent access concurrent access to the camera.
        self._capture_lock = threading.Lock()
        self._capture_thread = threading.Thread(target=self._grab_frames)
        self._capture_thread.daemon = True
        self._capture_thread.start()

    def _grab_frames(self):
        while True:
            with self._capture_lock:
                self._capture_frame = self.name
            time.sleep(1.0 / CAPTURE_HZ)

    def speak(self):
        print("Hi! My name is {self.name}.".format(self=self))

Here is result I'm testing:

$ python3
Python 3.5.3 (default, Sep 27 2018, 17:25:39)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import camera
>>> camera1 = camera.Camera("Cam1", 0)
Debug
>>> camera2 = camera.Camera("Cam2", 0) <<<<< It's stuck at here

And this process take 100% CPU of Raspberry. I must using sudo kill

Thank you because read my issue!

raspberry-pi opencv python
1 Answers

I found solution for solving this problem is using: Multiprocessing

We will create a server for manage camera for make sure in once time have only one camera running and can share camera between processes.

For example:

manager.py

import threading
import time
import cv2
from multiprocessing import Process
from multiprocessing.managers import BaseManager

CAPTURE_HZ = 30.0

class Camera(object):
    def __init__(self, name, id):
        self._camera = cv2.VideoCapture(id)
        print("Debug")
        self.name = name
        self._capture_frame = None
        # Use a lock to prevent access concurrent access to the camera.
        self._capture_lock = threading.Lock()
        self._capture_thread = threading.Thread(target=self._grab_frames)
        self._capture_thread.daemon = True
        self._capture_thread.start()

    def _grab_frames(self):
        while True:
            with self._capture_lock:
                self._capture_frame = self.name
            time.sleep(1.0 / CAPTURE_HZ)

    def speak(self):
        return self.name

class CameraManager(BaseManager):
   def __init__(self, address=None, authkey=''):
      BaseManager.__init__(self, address, authkey)
      self.camera = {}

   def addCamera(self, name, texture):
      self.camera[name] = texture

   def hasCamera(self, name):
      return name in self.camera

server.py

from multiprocessing import Process
from multiprocessing.managers import BaseManager
from manager import Camera, CameraManager

manager = CameraManager(address=('127.0.0.1', 50000), authkey=b'hello')

def getCamera(name): # Client always call to one function is getCamera
    if manager.hasCamera(name): # If camera already running -> return that camera
        print("Exist Camera")
        return manager.camera[name]
    else: # If camera not exist -> create the new one
        print("Create New Camera")
        camera = Camera(name, 0)
        manager.addCamera(name, camera)
        manager.register(name, lambda: camera)
        return manager.camera[name]

CameraManager.register("getCamera", getCamera)

if __name__ == "__main__":
    server = manager.get_server()
    server.serve_forever()

client.py

from multiprocessing import Process
from multiprocessing.managers import BaseManager
from manager import Camera, CameraManager

if __name__ == "__main__":
    manager = CameraManager(address=('127.0.0.1', 50000), authkey=b'hello')
    manager.connect()
    CameraManager.register("getCamera")
    camera = manager.getCamera("camera01")
    print("data = %s" % (camera.speak()))

And here is result I was tested:

$ python3 server.py

And run two process for client.py

$ python3 client.py

At that time my server.py will be

python3 server.py
Create New Camera
Debug
Exist Camera
Exist Camera

I was learned this tutorial from This Stackoverflow Thread. Thank you so much!

user_55303150
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