def recvfds(sock, size):
'''Receive an array of fds over an AF_UNIX socket.'''
a = array.array('i') #声明一个整型数组，itemsize
bytes_size = a.itemsize * size #数组容量设置
msg, ancdata, flags, addr = sock.recvmsg(1, socket.CMSG_LEN(bytes_size)) #从套接字中读取数据到msg，ancdata,recvmsg函数是标准posix函数，可以参阅：http://pubs.opengroup.org/onlinepubs/009695399/functions/recvmsg.html
if not msg and not ancdata:
raise EOFError
try:
if len(ancdata) != 1: #对于接收到的附加数据，长度不为1个元组的情况下退出
raise RuntimeError('received %d items of ancdata' %
len(ancdata))
cmsg_level, cmsg_type, cmsg_data = ancdata[0] #从附加数据中提取（cmsg_level, cmsg_type, cmsg_data）元组
if (cmsg_level == socket.SOL_SOCKET and
cmsg_type == socket.SCM_RIGHTS):
if len(cmsg_data) % a.itemsize != 0:
raise ValueError
a.frombytes(cmsg_data) #从cmsg_data中提取fd到数组a
assert len(a) % 256 == msg[0]
return list(a)
except (ValueError, IndexError):
pass
raise RuntimeError('Invalid data received')
