a pitfall in passing socket via processes
November 28th, 2007 :: jackyz
被问到一个奇怪的问题，做了一番探索，觉得还是有必要记录下来，以供来者参考。
如下的一个简单程序，会有什么问题？
下载: r3.erl
- -module(r3).
- -compile(export_all).
- start() ->
- spawn(r3, start, ["www.yahoo.com", 80]).
- start(RHost, RPort) ->
- io:format("start:pid=~p~n", [self()]),
- {ok, Sock} = gen_tcp:connect(RHost, RPort, [list, {packet, 0}, {active, false}, {reuseaddr, true}]),
- io:format("start:socket=~p~n", [erlang:port_info(Sock)]),
- spawn(r3, test, [Sock]).
- test(Sock) ->
- io:format("test:pid=~p~n", [self()]),
- io:format("socket=~p~n", [erlang:port_info(Sock)]),
- ok = gen_tcp:send(Sock, "GET / HTTP/1.0\r\n\r\n"),
- case gen_tcp:recv(Sock, 0) of
- {ok, Pack} ->
- io:format("recv:ok:~p~n", [Pack]);
- Any ->
- io:format("recv:~p~n", [Any])
- end,
- ok = gen_tcp:close(Sock).
OK，我知道这个简单的例子中，两个 spawn 都是没有必要的，实际上，不加这两个 spawn 一点问题也不会有，但是，加了似乎也没有什么明显的错误，不是么。那么，运行起来是怎样的呢？
1> r3:start().
start:pid=<0.33.0>
<0.33.0>
start:socket=[{name,"tcp_inet"},
{links,[<0.33.0>]},
{id,100},
{connected,<0.33.0>},
{input,0},
{output,0}]
test:pid=<0.37.0>
socket=undefined
2>
=ERROR REPORT==== 27-Nov-2007::22:04:57 ===
Error in process <0.37.0> with exit value: {{badmatch,{error,closed}},[{r3,test,1}]}
start:pid=<0.33.0>
<0.33.0>
start:socket=[{name,"tcp_inet"},
{links,[<0.33.0>]},
{id,100},
{connected,<0.33.0>},
{input,0},
{output,0}]
test:pid=<0.37.0>
socket=undefined
2>
=ERROR REPORT==== 27-Nov-2007::22:04:57 ===
Error in process <0.37.0> with exit value: {{badmatch,{error,closed}},[{r3,test,1}]}
是的，报了一个错，莫名奇妙啊，这是为什么呢？
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）表示感谢！
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