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本文链接地址: trace机制新增exception_trace
我们在使用Erlang的时候，经常会发现exception被静悄悄得忽略掉了，这点对于诊断问题非常的不友好。R14B04新添加exception_trace帮助用户在异常的时候，得到异常得调用栈，就马上可以解决问题。 这个功能主要面对高级用户，文档里面没怎么描述这个事情，主要的实现在erts的trace模块里面，有兴趣的同学可以自己看看。
我来演示下这个功能：
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本文链接地址: Erlang match_spec引擎介绍和应用
match_spec是什么呢？
A “match specification” (match_spec) is an Erlang term describing a small “program” that will try to match something (either the parameters to a function as used in the erlang:trace_pattern/2 BIF, or the objects in an ETS table.). The match_spec in many ways works like a small function in Erlang, but is interpreted/compiled by the Erlang runtime system to something much more efficient than calling an Erlang function. The match_spec is also very limited compared to the expressiveness of real Erlang functions.
具体参见这里
说白了它就是个erlang term得过滤器，可以让用户来自己选择需要匹配什么，需要从term里面抽取什么数据。那同学可能就有疑问了,Erlang的函数不是很强大吗,它能做的函数也能做，那为什么要重新费劲做一个呢？
Erlang实现这个match_spec得原因有2个：1. 运行效率 2. 小巧可以在运行期使用。
它的实现思路是: match_spec是个引擎，有自己的语法，先把语句编译成专用的opcode, 然后在在匹配的时候运行opcode,获取结果，可以理解为erlang的DSL。
接下来我带大家先感性的认识下这个DSL：
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本文链接地址: seq_trace集群消息链跟踪利器
做过网络集群服务器的的同学都知道，集群服务通常由不同的服务器组成，这些不同角色的服务器组合在一起共同完成了特定的服务。一个服务通常需要一个协调者，和不同的工作者。 协调者负责派发任务，接收工作者的完成情况，最终回馈给用户。举个例子来讲，拨打电话：首先需要确认你的号码是在有效的，同时还要看下你的帐号里面有钱不，还要看下你拨打的电话号码是不是由权限，电话打的时候需要扣钱，等等。 这些服务中间的任何一个环节出问题了，服务就不正常了。那么我们在服务出问题的时候，如何定位问题呢？通常的办法是打日志，在所有的参与服务的节点上打开日志记录，之后到所有的节点上收集日志，集中分析日志，相当的麻烦。
这时候seq_trace来救助了，seq_trace的目标就是能够跟踪一条消息经过的所有环节，最终把路径展现给用户。
铺垫材料：
seq_trace工作原理，请参考这里
ttb对seq_trace的支持参考这里
tdbg对seq_trace的支持参考这里
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本文链接地址: 如何找出异常所在的行(新思路)
在Erlang-china的邮件列表上看到这样的问题:
我的服务经常发生这样的错误,举例:
Error in process <0.33.0> with exit value: {badarg,[{erlang,’++’,[undefined,[{“37”}]]},{groups,doWork,1},
{groups,doWork,1},{groups,manage_clients,1}]}大意明白,但问题是我使用匹配机制时没考虑到多个函数”doWork/1″出错无法定位到其中一个,这该如何是好?
Erlang是否会像其它语言一样提示某一行出错?
这个问题确实很常见, Erlang的运行期没有给出出错的具体行数, 这给我们定位问题带来了很大的麻烦.
有先驱给出了这样的解决方案 http://mryufeng.javaeye.com/blog/368507 但是这个模块已经很老了, 过时不维护了.
这里我给出另外一个方案, 利用erlang现有的模块来实现的: cover + dbg
cover的工作原理可以参考这篇文章 http://mryufeng.javaeye.com/blog/482204.
原理就是cover编译过的模块会在每行执行前, 先执行ets:update_counter(cover_internal_data_table,{bump,Mod,Fun,1,1,Line},1) 来更新模块某行的执行次数.
那么我们只要截取 ets:update_counter这个动作, 我们就知道改模块最后的执行行, 也就是异常所在的行.
Ok, 原理介绍完毕, 上菜.
[root@centos ~]# cat line.erl
-module(line).
-export([dbg/1]).
-include_lib("stdlib/include/ms_transform.hrl").
dbg(Mod)->
cover:compile(Mod),
dbg:tracer(),
dbg:p(all, [call]),
dbg:tpl(ets,
update_counter,
dbg:fun2ms(fun([_,{bump,Mod,_,_,_,_},1]) ->
return_trace()
end)),
ok.
[root@centos ~]# cat hello.erl
-module(hello).
-export([start/0]).
start()->
a=a,
A=2,
C=3,
A=C-1,
C=A+1,
io:format("hello world~n",[]),
test(C),
ok.
test(C)->
A=4,
A=C, % Error is on this line.
ok.
我们可以看到这个hello模块会在hello:test发生异常, A=C这个地方是具体位置. 现在让我们找到行号:
[root@centos ~]# erl
Erlang R13B02 (erts-5.7.3) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
Eshell V5.7.3 (abort with ^G)
1> line:dbg(hello).
ok
2> hello:start().
hello world
** exception error: no match of right hand side value 3
in function hello:test/1
in call from hello:start/0
4> (<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,5},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,6},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,7},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,8},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,9},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,10},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,start,0,1,11},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,test,1,1,16},1)
(<0.34.0>) returned from ets:update_counter/3 -> 1
(<0.34.0>) call ets:update_counter(cover_internal_data_table,{bump,hello,test,1,1,17},1) %这里我们看到出错的行号
(<0.34.0>) returned from ets:update_counter/3 -> 1
3>
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
(v)ersion (k)ill (D)b-tables (d)istribution
我们可以看到最后一次执行hello模块的行数是17.
Bingo!
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本文链接地址: 从FTP模块学习先进的诊断技术(Erlang Trace机制)
我们开发好了一个软件的时候,通常是经过严格测试的,才分发给用户使用, 但是即使这样也不能保证用户的环境和我们的相同, 我们的软件还是会失败的. 问题是如何诊断这些问题.
通常的做法是写log,这是个很有效的方式. 但是写log要代码支持,而且会带来负面的性能影响. Erlang提供了强大的Trace机制, 帮助我们解决这个问题. OTP本身有很多模块利用了这个技术手段,我们从ftp模块学习下:
上代码:
lib/inets/src/ftp/ftp.erl
771 %% Maybe activate dbg
772 case key_search(debug, Options, disable) of
773 trace ->
774 dbg:tracer(),
775 dbg:p(all, [call]), %% 我们关心函数调用
776 dbg:tpl(ftp, [{'_', [], [{return_trace}]}]), %%以及返回值
777 dbg:tpl(ftp_response, [{'_', [], [{return_trace}]}]),
778 dbg:tpl(ftp_progress, [{'_', [], [{return_trace}]}]);
779 debug ->
780 dbg:tracer(),
781 dbg:p(all, [call]),
782 dbg:tp(ftp, [{'_', [], [{return_trace}]}]),
783 dbg:tp(ftp_response, [{'_', [], [{return_trace}]}]),
784 dbg:tp(ftp_progress, [{'_', [], [{return_trace}]}]);
785 _ ->
786 %% Keep silent
787 ok
788 end,
我们可以在启动参数里面加上debug标志, 在需要的时候打开这些诊断功能!
现在我们演示下,代码片段从inets userguide来的, 用户名密码不用试验了, 我不会告诉你的, 呵呵:
root@ubuntu:~# erl
Erlang R14A (erts-5.8) [source] [smp:2:2] [rq:2] [async-threads:0] [kernel-poll:false]
Eshell V5.8 (abort with ^G)
1> inets:start().
ok
2> {ok,Pid} = inets:start(ftpc, [{host,"ftp.yufeng.info"},{debug,debug}])
2> .
(<0.45.0>) call ftp:handle_call({<0.31.0>,
{open,ip_comm,
[{host,"ftp.yufeng.info"},
{progress,ignore},
{timeout,60000},
{ipfamily,inet},
{port,21},
{mode,passive}]}},{<0.31.0>,#Ref<0.0.0.45>},{state,undefined,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,inet,ignore})
(<0.45.0>) call ftp_progress:start_link(ignore)
(<0.45.0>) returned from ftp_progress:start_link/1 -> ignore
(<0.45.0>) returned from ftp:handle_call/3 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.45>},
open,inet,ignore},
59493}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,
<<"220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------\r\n220-You are user number 7 of 1000 allowed.\r\n220-Local time is now 02:33. Server port: 21.\r\n220-IPv6 connections are also welcome on this server.\r\n220 You will be disconnected after 15 minutes of inactivity.\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.45>},
open,inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------\r\n220-You are user number 7 of 1000 allowed.\r\n220-Local time is now 02:33. Server port: 21.\r\n220-IPv6 connections are also welcome on this server.\r\n220 You will be disconnected after 15 minutes of inactivity.\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------\r\n220-You are user number 7 of 1000 allowed.\r\n220-Local time is now 02:33. Server port: 21.\r\n220-IPv6 connections are also welcome on this server.\r\n220 You will be disconnected after 15 minutes of inactivity.\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------\r\n220-You are user number 7 of 1000 allowed.\r\n220-Local time is now 02:33. Server port: 21.\r\n220-IPv6 connections are also welcome on this server.\r\n220 You will be disconnected after 15 minutes of inactivity.\r\n")
{ok,<0.45.0>}
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_compl,
"---------- Welcome to Pure-FTPd [privsep] [TLS] ----------\r\n220-You are user number 7 of 1000 allowed.\r\n220-Local time is now 02:33. Server port: 21.\r\n220-IPv6 connections are also welcome on this server.\r\n220 You will be disconnected after 15 minutes of inactivity.\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,
inet,ignore}}
3> ftp:user(Pid, "username", "password").
(<0.31.0>) call ftp:user(<0.45.0>,"username","password")
(<0.45.0>) call ftp:handle_call({<0.31.0>,{user,"username","password"}},{<0.31.0>,#Ref<0.0.0.64>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,inet,ignore})
(<0.45.0>) returned from ftp:handle_call/3 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.64>},
{handle_user,"password",[]},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,<<"331 User yufengin OK. Password required\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.64>},
{handle_user,"password",[]},
inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"331 User yufengin OK. Password required\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"331 User yufengin OK. Password required\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("331 User yufengin OK. Password required\r\n")
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_interm,
" User yufengin OK. Password required\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.64>},
{handle_user_passwd,[]},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,
<<"230-User yufengin has group access to: yufengin \r\n230 OK. Current restricted directory is /\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.64>},
{handle_user_passwd,[]},
inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"230-User yufengin has group access to: yufengin \r\n230 OK. Current restricted directory is /\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"230-User yufengin has group access to: yufengin \r\n230 OK. Current restricted directory is /\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("230-User yufengin has group access to: yufengin \r\n230 OK. Current restricted directory is /\r\n")
ok
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_compl,
"-User yufengin has group access to: yufengin \r\n230 OK. Current restricted directory is /\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,
inet,ignore}}
(<0.31.0>) returned from ftp:user/3 -> ok
4>
4> ftp:pwd(Pid).
(<0.31.0>) call ftp:pwd(<0.45.0>)
(<0.45.0>) call ftp:handle_call({<0.31.0>,pwd},{<0.31.0>,#Ref<0.0.0.84>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,inet,ignore})
(<0.45.0>) returned from ftp:handle_call/3 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.84>},
pwd,inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,<<"257 \"/\" is your current location\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.84>},
pwd,inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"257 \"/\" is your current location\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"257 \"/\" is your current location\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("257 \"/\" is your current location\r\n")
{ok,"/"}
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_compl,
" \"/\" is your current location\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,
inet,ignore}}
(<0.31.0>) returned from ftp:pwd/1 -> {ok,"/"}
7> ftp:recv(Pid, "favicon.ico").
(<0.31.0>) call ftp:recv(<0.45.0>,"favicon.ico")
(<0.45.0>) call ftp:handle_call({<0.31.0>,{recv,"favicon.ico","favicon.ico"}},{<0.31.0>,#Ref<0.0.0.120>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.112>},
undefined,inet,ignore})
(<0.45.0>) returned from ftp:handle_call/3 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{setup_data_connection,
{recv_file,"favicon.ico",
{file_descriptor,prim_file,
{#Port<0.1087>,9}}}},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,
<<"227 Entering Passive Mode (74,220,215,202,156,59)\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{setup_data_connection,
{recv_file,"favicon.ico",
{file_descriptor,prim_file,{#Port<0.1087>,9}}}},
inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"227 Entering Passive Mode (74,220,215,202,156,59)\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"227 Entering Passive Mode (74,220,215,202,156,59)\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("227 Entering Passive Mode (74,220,215,202,156,59)\r\n")
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_compl,
" Entering Passive Mode (74,220,215,202,156,59)\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
#Port<0.1093>,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,
{file_descriptor,prim_file,
{#Port<0.1087>,9}}},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,<<"150 Accepted data connection\r\n">>},{state,#Port<0.1086>,#Port<0.1093>,false,"/root",ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,{file_descriptor,prim_file,{#Port<0.1087>,9}}},
inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"150 Accepted data connection\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"150 Accepted data connection\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("150 Accepted data connection\r\n")
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_prel,
" Accepted data connection\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
#Port<0.1093>,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,
{file_descriptor,prim_file,
{#Port<0.1087>,9}}},
inet,ignore}}
ok
8> (<0.45.0>) call ftp:handle_info({tcp,#Port<0.1093>,
<<71,73,70,56,57,97,1,0,1,0,128,0,0,255,255,255,255,255,255,33,249,4,1,7,
0,1,0,44,0,0,0,0,1,0,1,0,0,2,2,76,1,0,59>>},{state,#Port<0.1086>,#Port<0.1093>,false,"/root",ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,{file_descriptor,prim_file,{#Port<0.1087>,9}}},
inet,ignore})
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
#Port<0.1093>,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,
{file_descriptor,prim_file,
{#Port<0.1087>,9}}},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp_closed,#Port<0.1093>},{state,#Port<0.1086>,#Port<0.1093>,false,"/root",ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,{file_descriptor,prim_file,{#Port<0.1087>,9}}},
inet,ignore})
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,
{file_descriptor,prim_file,
{#Port<0.1087>,9}}},
inet,ignore}}
(<0.45.0>) call ftp:handle_info({tcp,#Port<0.1086>,
<<"226-File successfully transferred\r\n226 0.020 seconds (measured here), 2.07 Kbytes per second\r\n">>},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,
{<0.31.0>,#Ref<0.0.0.120>},
{recv_file,{file_descriptor,prim_file,{#Port<0.1087>,9}}},
inet,ignore})
(<0.45.0>) call ftp_response:parse_lines(<<"226-File successfully transferred\r\n226 0.020 seconds (measured here), 2.07 Kbytes per second\r\n">>,[],start)
(<0.45.0>) returned from ftp_response:parse_lines/3 -> {ok,
"226-File successfully transferred\r\n226 0.020 seconds (measured here), 2.07 Kbytes per second\r\n",
<<>>}
(<0.45.0>) call ftp_response:interpret("226-File successfully transferred\r\n226 0.020 seconds (measured here), 2.07 Kbytes per second\r\n")
(<0.45.0>) returned from ftp_response:interpret/1 -> {pos_compl,
"-File successfully transferred\r\n226 0.020 seconds (measured here), 2.07 Kbytes per second\r\n"}
(<0.45.0>) returned from ftp:handle_info/2 -> {noreply,
{state,#Port<0.1086>,
undefined,false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,
inet,ignore}}
(<0.31.0>) returned from ftp:recv/2 -> ok
8> inets:stop(ftpc, Pid).
ok
9> (<0.31.0>) call ftp:stop_service(<0.45.0>)
(<0.31.0>) returned from ftp:stop_service/1 -> ok
(<0.45.0>) call ftp:handle_cast({<0.31.0>,close},{state,#Port<0.1086>,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,inet,ignore})
(<0.45.0>) returned from ftp:handle_cast/2 -> {stop,normal,
{state,undefined,undefined,
false,"/root",
ftp_server_default,false,
passive,60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,
inet,ignore}}
(<0.45.0>) call ftp:terminate(normal,{state,undefined,undefined,false,"/root",ftp_server_default,false,passive,
60000,<<>>,
{<<>>,[],start},
<0.31.0>,undefined,undefined,inet,ignore})
(<0.45.0>) returned from ftp:terminate/2 -> ok
9> h().
1: inets:start()
-> ok
2: {ok,Pid} =
inets:start(ftpc, [{host,"ftp.yufeng.info"},{debug,debug}])
-> {ok,<0.45.0>}
3: ftp:user(Pid, "username", "password")
-> ok
4: ftp:pwd(Pid)
-> {ok,"/"}
5: ftp:cd(Pid, "public_html")
-> ok
6: ftp:lpwd(Pid)
-> {ok,"/root"}
7: ftp:recv(Pid, "favicon.ico")
-> ok
8: inets:stop(ftpc, Pid)
-> ok
Bingo! 我们非常的清楚了看到了整个系统交互的流程. 不废吹灰之力.
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原创文章，转载请注明： 转载自系统技术非业余研究
本文链接地址: erlang的profile工具原理和优缺点
erlang的tools application下包含了一系列的profile工具， 包括 eprof cprof fprof， 具体的使用可以参看文档和<< erlang effective guide>>.
我这里要说的是他们的工作原理。 这些模块的核心都是根据erlang的trace机制实现的。在模块执行的时候，trace机制会通知那个函数被调用 返回。根据这些信息就可以统计出来函数调用的频度，调用栈等。
但是利用这个机制会有严重的性能损失。因为每个函数调用都要发送一条trace信息，每个trace 信息会引起上下文切换 而且要耗费2-3的时间。这个对大型的系统是不可接受的。
所以知道这些原理以后， 我们在profile大型的系统的时候，我们可以在dbg模块的帮助下， 只收集我们感兴趣的东西，而且严格限定范围，避免对系统造成大的干扰，这样收集出来的东西才有意义。
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