performance problem of streaming data over TCP

[Changhao]

Hi, friends,

     I am implementing a protocol on top of 'asyncore.dispatcher' to 
send streaming multimedia data over TCP socket. However, I found that 
the throughput of my current implementation is surprisingly low.

     Below is a snippet of my code with a note that: the packet sent 
over the socket is of variable length, of which the first a couple bytes 
indicates the length of the packet. I implemented a 'var_str_to_int' 
function to get the 'length' and the offset of the payload.

###############################################
   def handle_read(self):
     self.socket.setblocking(1)
     while (True) :
 
 
                                                                data = 
self.assemble_msg()
         if (not data) :
             self.socket.setblocking(0)
             return
         (length,index) = var_str_to_int(data)
         self._dispatch_cmd(data[index:])
         if (not self.recv_buffer) :
            break
     self.socket.setblocking(0)

   def assemble_msg(self) :
      if (self.recv_buffer) :
           data = self.recv_buffer
      else :
           data = self.socket.recv(self.BUFFER_SIZE)
           if (len(data) == 0) :
               return None
      length,index = var_str_to_int(data)
      while (length +index > len(data)) :
          data += self.socket.recv(self.BUFFER_SIZE)
      if (length + index == len(data)) :
          self.recv_buffer = ''
      else :
          self.recv_buffer = data[length+index:]
          data = data[:length+index]
      return data
###############################################

     I found it took around 7 seconds to receive a packet of 40KB sent 
from localhost. The throughput is even not enough to support any 
streaming multimedia file for live playback in a LAN.

     I read some threads in the group. It sounds like the problem might 
have to do with the TCP option, setting TCP_NODELAY probably could solve 
the problem. But I tried the following on both a Linux and a windows XP 
machine. Neither of them worked:

##############################################
self.socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
##############################################

     Any comments or suggests is highly appreciated.

     Thanks,
     Changhao