I've tested it on Windows XP. MSG_WAITALL is not supported, but I 
replaced it using a while loop. I didn't notice any extraneous delay.

500 packets @ 2 tokens each (500 very short lists)
0.140999794006
         16008 function calls in 0.146 CPU seconds

   Ordered by: internal time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     1500    0.036    0.000    0.036    0.000 {method 'recv' of 
'_socket.socket'
 objects}
     1500    0.033    0.000    0.033    0.000 <string>:1(sendall)
     1500    0.016    0.000    0.065    0.000 Client.py:15(read_int)
     1500    0.015    0.000    0.053    0.000 Client.py:7(send_int)
      500    0.009    0.000    0.077    0.000 
Client.py:22(read_int_list)
      500    0.007    0.000    0.060    0.000 
Client.py:10(send_int_list)
     1500    0.007    0.000    0.010    0.000 struct.py:77(unpack)
     1500    0.005    0.000    0.005    0.000 struct.py:54(pack)
      500    0.004    0.000    0.141    0.000 Client.py:31(spam)
     2001    0.004    0.000    0.004    0.000 {len}
        1    0.003    0.003    0.146    0.146 runme.py:11(bench)
     1500    0.003    0.000    0.003    0.000 {method 'unpack' of 
'Struct' objec
ts}
     1001    0.003    0.000    0.003    0.000 {range}
     1000    0.002    0.000    0.002    0.000 {method 'append' of 
'list' objects
}
        1    0.000    0.000    0.000    0.000 struct.py:35(_compile)
        2    0.000    0.000    0.000    0.000 {time.time}
        1    0.000    0.000    0.146    0.146 <string>:1(<module>)
        1    0.000    0.000    0.000    0.000 {method 'disable' of 
'_lsprof.Prof
iler' objects}


None
================================================================================


1 packet @ 50000 tokens (1 very long list)
4.89100003242
         450019 function calls in 4.893 CPU seconds

   Ordered by: internal time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
    50001    1.212    0.000    1.212    0.000 <string>:1(sendall)
    50001    1.062    0.000    1.062    0.000 {method 'recv' of 
'_socket.socket'
 objects}
    50001    0.594    0.000    2.282    0.000 Client.py:15(read_int)
    50001    0.517    0.000    1.982    0.000 Client.py:7(send_int)
        1    0.354    0.354    2.732    2.732 
Client.py:22(read_int_list)
    50001    0.335    0.000    0.524    0.000 struct.py:77(unpack)
    50001    0.253    0.000    0.253    0.000 struct.py:54(pack)
    50001    0.189    0.000    0.189    0.000 {method 'unpack' of 
'Struct' objec
ts}
        1    0.176    0.176    2.158    2.158 
Client.py:10(send_int_list)
    50002    0.102    0.000    0.102    0.000 {len}
    50000    0.097    0.000    0.097    0.000 {method 'append' of 
'list' objects
}
        2    0.002    0.001    0.002    0.001 {range}
        1    0.002    0.002    4.893    4.893 runme.py:19(bench2)
        1    0.000    0.000    4.890    4.890 Client.py:31(spam)
        2    0.000    0.000    0.000    0.000 {time.time}
        1    0.000    0.000    4.893    4.893 <string>:1(<module>)
        1    0.000    0.000    0.000    0.000 {method 'disable' of 
'_lsprof.Prof
iler' objects}