erlang-python port 程序

阿斯顿阿斯顿

把<Programming Erlang>书上第12章那个erlang-c的例子改编了下，把C程序改写成了python程序。在ubuntu8.04 + erlang5.6.5 + python2.5.2上调试通过。
erlang side: example2.erl
-module(example2).
-export([start/0, stop/0]).
-export([twice/1, sum/2]).
start() ->
spawn(fun() ->
register(example1, self()),
process_flag(trap_exit, true),
Port = open_port({spawn, "python -u ./example2.py"}, [{packet, 2}]),
loop(Port)
end).
stop() ->
example1 ! stop.
twice(X) -> call_port({twice, X}).
sum(X,Y) -> call_port({sum, X, Y}).
call_port(Msg) ->
example1 ! {call, self(), Msg},
receive
{example1, Result} ->
Result
end.
loop(Port) ->
receive
{call, Caller, Msg} ->
Port ! {self(), {command, encode(Msg)}},
receive
{Port, {data, Data}} ->
Caller ! {example1, decode(Data)}
end,
loop(Port);
stop ->
Port ! {self(), close},
receive
{Port, closed} ->
exit(normal)
end;
{'EXIT', Port, Reason} ->
exit({port_terminated,Reason})
end.
encode({twice, X}) -> [1, X];  
encode({sum, X, Y}) -> [2, X, Y].
decode([Int]) -> Int.

需要注意的是调用python程序，要使用参数－u。强制标准输入／输出不得有缓存，要立时反应。
python官方文档对-u的解释: Force stdin, stdout and stderr to be totally unbuffered.

python side: example2.py
import sys, os
import struct
def recv():
buf = sys.stdin.read(2)
if len(buf) == 2:
(sz, ) = struct.unpack("!h", buf)
payload = sys.stdin.read(sz)
return payload
else:
return None
def send(payload):
sz = len(payload)
header= struct.pack("!h", sz)
return sys.stdout.write( header + payload )
def twice(arg1):
return 2*arg1
def sum(arg1,arg2):
return arg1+arg2
def main_loop():
buf = recv()
while buf:
xa = struct.unpack("!%dB" % len(buf), buf)
if xa[0] == 1:
calc_res = twice(xa[1])
elif xa[0] == 2:
calc_res = sum(xa[1], xa[2])
result = struct.pack('!B', calc_res)
send(result)
buf = recv()
return None
if __name__ == '__main__':
main_loop()