python - python Queue.Queue 和 multiprocessing.Queue 的区别

Question

当我使用多处理模块(Windows 上的 Python 2.7)中的队列代替 Queue.Queue 时，我的程序没有完全关闭。

最终，我想使用 multiprocessing.Process 处理 imgbuffer 中的帧，然后使用第二个队列拉回显示数据。这还不起作用 - 似乎 Process.start() 什么都不做 - 但由于我在调试多处理代码时遇到了麻烦，我想我会削减我拥有的最简单的代码，看看是否有人有关于下一步尝试的想法。

import sys
from PySide import QtGui, QtCore
import cv2
import time, datetime
import multiprocessing
import Queue #needed separately for the Empty exception

def imageOpenCv2ToQImage(cv_img):
   height, width, bytesPerComponent = cv_img.shape
   bytesPerLine = bytesPerComponent * width;
   cv2.cvtColor(cv_img, cv2.cv.CV_BGR2RGB, cv_img)
   return QtGui.QImage(cv_img.data, width, height, bytesPerLine, QtGui.QImage.Format_RGB888)

class VideoWidget(QtGui.QLabel):
   def __init__(self):
      super(VideoWidget, self).__init__()

      self.imgbuffer = multiprocessing.Queue() 
      ############################################
      # hangs on quit using multiprocessing.Queue
      # works fine when I use Queue.Queue
      #########################################

      self.camera = cv2.VideoCapture(1) # camera ID depends on system: 0, 1, etc

      self.setGeometry(100, 100, 640, 480)
      self.setScaledContents(True)

      target_FPS = 30.0
      self.camera_timer = QtCore.QTimer()
      self.camera_timer.timeout.connect(self.on_camera_timer)
      self.camera_timer.start(1000.0/target_FPS)

      target_FPS = 40.0
      self.repaint_timer = QtCore.QTimer()
      self.repaint_timer.timeout.connect(self.on_repaint_timer)
      self.repaint_timer.start(1000.0/target_FPS)

   def shutdown(self):
      self.camera.release()

   def on_camera_timer(self):
      hello, cv_img = self.camera.read()
      tstamp = datetime.datetime.now()
      self.imgbuffer.put((tstamp, cv_img))

   def on_repaint_timer(self):
      try:
         tstamp, cv_img = self.imgbuffer.get(False)
         pixmap = QtGui.QPixmap.fromImage(imageOpenCv2ToQImage(cv_img))
         self.setPixmap(pixmap)
      except Queue.Empty:
         pass

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    widget = VideoWidget()
    app.aboutToQuit.connect(widget.shutdown)
    widget.show()
    sys.exit(app.exec_())

Answer 1

我想通了……答案毕竟在文档中:

https://docs.python.org/3/library/multiprocessing.html#pipes-and-queues

尤其:

They differ in that Queue lacks the task_done() and join() methods introduced into Python 2.5’s queue.Queue class.

就我而言，解决方案似乎是将其添加到关闭代码中:

self.imgbuffer.cancel_join_thread()