在Python中使用多处理时，只执行两个进程

Question

我在python中使用套接字编写了两个系统之间的视频共享代码。我分叉了4个进程，每个进程执行以下任务：记录帧，发送记录的帧，接收帧，播放接收的帧。 这是我的代码：

import socket
import cv2
import time
from threading import Thread
from multiprocessing import Process, Queue
import sys
import pickle
import numpy as np
import zlib

HOST="192.168.43.42"
PORT=1060
MAX=65535
frames_record=Queue()
frames_play=Queue()
s=socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

#data_to_decomp=""

def record(frames_record):
    cap = cv2.VideoCapture(0)
    cap.set(3, 160)#reducing width
    cap.set(4, 120)#reducing height
    compressed_frame=""#frames to compress

    while (cap.isOpened()):
        ret, frame=cap.read()
        print "HERE 1"
        compressed_frame=zlib.compress(pickle.dumps(frame))+"end"
        frames_record.put(compressed_frame)
        compressed_frame=""
        #if cv2.waitKey(0) & 0xFF == ord('q'):
        #   break
        time.sleep(0.0001)
    cap.release()


def send(sock, addr, frames_record):
    while True:
        if not frames_record.empty():
            print "in send"
            #print sys.getsizeof(frames_record[0])
            #print len(frames_record[0])
            #print frames_record[0]
            sock.sendto((frames_record.get()), addr)
            time.sleep(0.0001)

def play(frames_play):
    print "in play"
    while True:
        if not frames_play.empty()>0:
            print "in playing"
            frame=frames_play.get()
            cv2.imshow("chat", frame)           
            if cv2.waitKey(1) & 0xFF == ord('q'):
                break
            time.sleep(0.0001)
    cv2.destroyAllWindows()

def recv_all(sock, frames_play):
    print "in recv_all"
    msg=""
    while True:     
        while "end" not in msg:
            print "in recv_all"
            data, addr=sock.recvfrom(MAX)       
            msg+=data
        index=msg.find("end")
        decompressed_frame=zlib.decompress(msg[:index])#frames to decompress

        frames_play.put(pickle.loads(decompressed_frame))
        if not msg.endswith("end"):         
            msg=msg[index+3:]
        else:
            msg=""
        time.sleep(0.0001)


if sys.argv[1] == "server":
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind(("", PORT))

    t_recv=Process(target=recv_all, args=(s, frames_play,))
    t_play=Process(target=play, args=(frames_play,))
    #t_recv.setDaemon(True)
    #t_play.setDaemon(True)

    t_record=Process(target=record, args=(frames_record,))
    t_send=Process(target=send, args=(s,(HOST, PORT), frames_record,))
    #t_record.setDaemon(True)
    #t_send.setDaemon(True)
    t_record.start()    
    t_recv.start()
    t_play.start()
    t_send.start()


    t_record.join()
    t_send.join()

    t_recv.join()
    t_play.join()
    s.close()


elif sys.argv[1] == "client":
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind(("", PORT))  
    #s.connect((HOST, PORT))    

    t_record=Process(target=record, args=(frames_record,))
    t_send=Process(target=send, args=(s,(HOST, PORT), frames_record,))
    #t_record.setDaemon(True)
    #t_send.setDaemon(True)


    t_recv=Process(target=recv_all, args=(s, frames_play,))
    t_play=Process(target=play, args=(frames_play,))
    #t_recv.setDaemon(True)
    #t_play.setDaemon(True)

    t_record.start()
    t_send.start()
    t_recv.start()
    t_play.start()


    t_recv.join()
    t_play.join()
    t_record.join()
    t_send.join()
    s.close()
else:
    print "Error: Usage: python filename.py <server/client>"

当我在两个独立的系统上运行此代码时，我发现（使用print语句）大多数情况下程序在两个系统中都卡在t_record和t_send中。我无法理解为什么控件不会转移到其他两个进程（t_recv和t_play）。

PS：我也尝试过线程，它也没有用。两个系统上的视频都在第一帧上冻结，我不得​​不强制停止这个过程。