socket.so_reuseaddr:每个vs由最新的侦听器接收的数据包

我有多个进程在订阅多播地址的同一端口上侦听。到这个地址的数据包到达每个进程。但是,当我通过单播与他们联系时,只有最新的进程会收到消息。在哪里记录这种行为?我怎样才能改变它?

演示程序(python):

import socket,os,struct,sys

def server():
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind(('', 4242))

    mreq = '\xef\x01\x02\x03' + struct.pack('=I', socket.INADDR_ANY)
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

    while True:
        d = sock.recvfrom(1024)
        print('[s' + str(os.getpid()) + '] ' + repr(d))

def client():
    caddr = '239.1.2.3'
    caddr = '127.0.0.1' # Uncomment this and all servers print
    csock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    csock.sendto('data from ' + str(os.getpid()), 0, (caddr, 4242))

def main():
    if sys.argv[1] == 's':
        server()
    else:
        client()

if __name__ == '__main__':
    main()