drf*_*oob 8 erlang erlang-otp gen-server erlang-supervisor
我正在研究Erlang文档,试图了解设置OTP gen_server和supervisor的基础知识.每当我的gen_server崩溃时,我的主管也会崩溃.事实上,每当我在命令行上出错时,我的主管就会崩溃.
我希望gen_server在崩溃时重新启动.我希望命令行错误对我的服务器组件没有任何影响.我的主管不应该崩溃.
我正在使用的代码是一个基本的"回声服务器",它回复你发送的任何内容,以及一个主管,它最多每分钟重启一次echo_server 5次(one_for_one).我的代码:
echo_server.erl
-module(echo_server).
-behaviour(gen_server).
-export([start_link/0]).
-export([echo/1, crash/0]).
-export([init/1, handle_call/3, handle_cast/2]).
start_link() ->
gen_server:start_link({local, echo_server}, echo_server, [], []).
%% public api
echo(Text) ->
gen_server:call(echo_server, {echo, Text}).
crash() ->
gen_server:call(echo_server, crash)..
%% behaviours
init(_Args) ->
{ok, none}.
handle_call(crash, _From, State) ->
X=1,
{reply, X=2, State}.
handle_call({echo, Text}, _From, State) ->
{reply, Text, State}.
handle_cast(_, State) ->
{noreply, State}.
echo_sup.erl
-module(echo_sup).
-behaviour(supervisor).
-export([start_link/0]).
-export([init/1]).
start_link() ->
supervisor:start_link(echo_sup, []).
init(_Args) ->
{ok, {{one_for_one, 5, 60},
[{echo_server, {echo_server, start_link, []},
permanent, brutal_kill, worker, [echo_server]}]}}.
编译使用erlc *.erl,这是一个示例运行:
Erlang R13B01 (erts-5.7.2) [source] [smp:2:2] [rq:2] [async-threads:0] [kernel-p
oll:false]
Eshell V5.7.2 (abort with ^G)
1> echo_sup:start_link().
{ok,<0.37.0>}
2> echo_server:echo("hi").
"hi"
3> echo_server:crash().
=ERROR REPORT==== 5-May-2010::10:05:54 ===
** Generic server echo_server terminating
** Last message in was crash
** When Server state == none
** Reason for termination ==
** {'function not exported',
[{echo_server,terminate,
[{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]},
none]},
{gen_server,terminate,6},
{proc_lib,init_p_do_apply,3}]}
=ERROR REPORT==== 5-May-2010::10:05:54 ===
** Generic server <0.37.0> terminating
** Last message in was {'EXIT',<0.35.0>,
{{{undef,
[{echo_server,terminate,
[{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]},
none]},
{gen_server,terminate,6},
{proc_lib,init_p_do_apply,3}]},
{gen_server,call,[echo_server,crash]}},
[{gen_server,call,2},
{erl_eval,do_apply,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
** When Server state == {state,
{<0.37.0>,echo_sup},
one_for_one,
[{child,<0.41.0>,echo_server,
{echo_server,start_link,[]},
permanent,brutal_kill,worker,
[echo_server]}],
{dict,0,16,16,8,80,48,
{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],
[]},
{{[],[],[],[],[],[],[],[],[],[],[],[],[],[],
[],[]}}},
5,60,
[{1273,79154,701110}],
echo_sup,[]}
** Reason for termination ==
** {{{undef,[{echo_server,terminate,
[{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]},
none]},
{gen_server,terminate,6},
{proc_lib,init_p_do_apply,3}]},
{gen_server,call,[echo_server,crash]}},
[{gen_server,call,2},
{erl_eval,do_apply,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}
** exception exit: {{undef,
[{echo_server,terminate,
[{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]},
none]},
{gen_server,terminate,6},
{proc_lib,init_p_do_apply,3}]},
{gen_server,call,[echo_server,crash]}}
in function gen_server:call/2
4> echo_server:echo("hi").
** exception exit: {noproc,{gen_server,call,[echo_server,{echo,"hi"}]}}
in function gen_server:call/2
5>
小智 15
测试来自shell的主管的问题是主管进程链接到shell进程.当gen_server进程崩溃时,退出信号会传播到shell崩溃并重新启动.
为避免此问题,请向主管添加以下内容:
start_in_shell_for_testing() ->
{ok, Pid} = supervisor:start_link(echo_sup, []),
unlink(Pid).
我建议你调试/跟踪你的应用程序以检查发生了什么.这对于了解OTP中的工作原理非常有帮助.
在您的情况下,您可能希望执行以下操作.
启动跟踪器:
dbg:tracer().
跟踪您的主管和gen_server的所有函数调用:
dbg:p(all,c).
dbg:tpl(echo_server, x).
dbg:tpl(echo_sup, x).
检查进程传递的消息:
dbg:p(new, m).
查看您的流程发生了什么(崩溃等):
dbg:p(new, p).
有关跟踪的更多信息:
http://www.erlang.org/doc/man/dbg.html
http://aloiroberto.wordpress.com/2009/02/23/tracing-erlang-functions/
希望这可以为这个和未来的情况提供帮助.
提示: gen_server行为期望定义和导出回调终止/ 2;)
更新:在终止/ 2的定义之后,从跟踪中可以看出崩溃的原因.这是它的样子:
我们(75)调用crash/0函数.这由gen_server(78)接收.
(<0.75.0>) call echo_server:crash()
(<0.75.0>) <0.78.0> ! {'$gen_call',{<0.75.0>,#Ref<0.0.0.358>},crash}
(<0.78.0>) << {'$gen_call',{<0.75.0>,#Ref<0.0.0.358>},crash}
(<0.78.0>) call echo_server:handle_call(crash,{<0.75.0>,#Ref<0.0.0.358>},none)
呃,句柄调用问题.我们有一个坏人......
(<0.78.0>) exception_from {echo_server,handle_call,3} {error,{badmatch,2}}
调用terminate函数.服务器退出并且未注册.
(<0.78.0>) call echo_server:terminate({{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]},none)
(<0.78.0>) returned from echo_server:terminate/2 -> ok
(<0.78.0>) exit {{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]}
(<0.78.0>) unregister echo_server
Supervisor(77)从gen_server接收退出信号并完成其工作:
(<0.77.0>) << {'EXIT',<0.78.0>,
{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]}}
(<0.77.0>) getting_unlinked <0.78.0>
(<0.75.0>) << {'DOWN',#Ref<0.0.0.358>,process,<0.78.0>,
{{badmatch,2},
[{echo_server,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]}}
(<0.77.0>) call echo_server:start_link()
嗯,它试图...因为它发生了菲利波所说的......