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我打印了所有加载的代码如下，为什么{lager_default_tracer，[]}，梁文件在哪里？

(lager_test_1@macbook.local)10> io:format("~p",[code:all_loaded()]).
[{io,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/io.beam"},
 {erl_distribution,"/usr/local/lib/erlang/lib/kernel-3.1/ebin/erl_distribution.beam"},
 {edlin,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/edlin.beam"},
 {beam_clean,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/beam_clean.beam"},
 {v3_core,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/v3_core.beam"},
 {erl_epmd,"/usr/local/lib/erlang/lib/kernel-3.1/ebin/erl_epmd.beam"},
 {love_misc,"/usr/local/bin/lager_test/lib/hanoch-0.0.1.6/ebin/love_misc.beam"},
 {zlib,preloaded},
 {error_handler,"/usr/local/lib/erlang/lib/kernel-3.1/ebin/error_handler.beam"},
 {io_lib,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/io_lib.beam"},
 {lib,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/lib.beam"},
 {mnesia,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia.beam"},
 {lager_test_app,"/usr/local/bin/lager_test/lib/lager_test-0.0.1.0/ebin/lager_test_app.beam"},
 {beam_jump,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/beam_jump.beam"},
 {v3_codegen,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/v3_codegen.beam"},
 {beam_flatten,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/beam_flatten.beam"},
 {mnesia_tm,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_tm.beam"},
 {prim_eval,preloaded},
 {beam_bool,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/beam_bool.beam"},
 {error_logger_lager_h,"/usr/local/bin/lager_test/lib/lager-2.0.0/ebin/error_logger_lager_h.beam"},
 {lager_msg,"/usr/local/bin/lager_test/lib/lager-2.0.0/ebin/lager_msg.beam"},
 {mnesia_frag,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_frag.beam"},
 {filename,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/filename.beam"},
 {lager_default_tracer,[]},
 {lager_default_formatter,"/usr/local/bin/lager_test/lib/lager-2.0.0/ebin/lager_default_formatter.beam"},
 {mnesia_locker,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_locker.beam"},
 {mnesia_recover,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_recover.beam"},
 {mnesia_dumper,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_dumper.beam"},
 {mnesia_kernel_sup,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_kernel_sup.beam"},
 {mnesia_sp,"/usr/local/lib/erlang/lib/mnesia-4.12.4/ebin/mnesia_sp.beam"},
 {erts_internal,preloaded},
 {unicode,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/unicode.beam"},
 {lager_backend_throttle,"/usr/local/bin/lager_test/lib/lager-2.0.0/ebin/lager_backend_throttle.beam"},
 {beam_type,"/usr/local/lib/erlang/lib/compiler-5.0.3/ebin/beam_type.beam"},
 {orddict,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/orddict.beam"},
 {gb_sets,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/gb_sets.beam"},
 {sofs,"/usr/local/lib/erlang/lib/stdlib-2.3/ebin/sofs.beam"},
 {inet_db,"/usr/local/lib/erlang/lib/kernel-3.1/ebin/inet_db.beam"},
 {lager_test_a,"/usr/local/bin/lager_test/lib/lager_test-0.0.1.0/ebin/lager_test_a.beam"},
 {inet,"/usr/local/lib/erlang/lib/kernel-3.1/ebin/inet.beam"},

当我调用 module_info() 时，如下所示：

(lager_test_1@macbook.local)11> lager_default_tracer:module_info().
[{exports,[{table,1},
           {handle,1},
           {module_info,0},
           {module_info,1},
           {info,1}]},
 {imports,[]},
 {attributes,[{vsn,[203040246025344403396962742072895880482]}]},
 {compile,[{options,[]},
           {version,"5.0.3"},
           {time,{2017,8,27,5,43,32}},
           {source,"/private/tmp/lager_test-0.0.1.0"}]}]

当我打电话lager_default_tracer:table(111)时，如下所示：

(lager_test_1@macbook.local)12> lager_default_tracer:table(aaa).
** exception error: bad argument
     in function  lager_default_tracer:table/1
4

1 回答 1

4

该lager_default_tracer模块没有关联的梁文件，因为它是在运行时创建的。lager应用程序使用，goldrush它使用运行时代码编译和加载。

如果您查看goldrush源代码，您会发现它调用了compile:forms/2动态编译的标准。通过跟踪该调用，我们可以重构源代码以lager_default_tracer使用以下步骤，假设您已经克隆了lager源存储库并成功编译它。在某些步骤中，Erlang shell 命令的输出太大，无法放在这里，所以这些部分使用省略号进行缩写。

  1. 在您已经编译的克隆lagerrepo 目录中，运行rebar shell以启动 Erlang shell，它确保所有必要的目录都在 Erlang 加载路径中。

  2. 在 shell 中，打开dbg跟踪和跟踪compile:forms/2：

    1> dbg:tracer(), dbg:p(all, call).
{ok,[{matched,nonode@nohost,34}]}
2> dbg:tpl(compile, forms, []).
{ok,[{matched,nonode@nohost,2}]}

  3. 启动lager应用程序及其依赖项：

    3> application:ensure_all_started(lager).

    这将导致dbg跟踪产生一些冗长的输出，如下所示：

    (<0.94.0>) call compile:forms([{attribute,0,module,lager_default_tracer}, ... {tuple,0,[{integer,0,2},{integer,0,1}]}]}]}]}],[nowarn_unused_vars]) {ok,[syntax_tools,compiler,goldrush,lager]} 08:29:21.478 [info] Application lager started on node nonode@nohost

    在这里，输出被缩写为仅显示第一行和最后几行。最后两行是application:ensure_all_started/1. 这些行之上的所有内容都是模块的抽象格式。lager_default_tracer

  4. 将跟踪的输出从[{attribute,0,module,lager_default_tracer}输出跟踪的第一行一直复制到输出跟​​踪{tuple,0,[{integer,0,2},{integer,0,1}]}]}]}]}]的最后一行。不要在复制的内容中包含结尾文本[nowarn_unused_vars])。

  5. M粘贴复制的数据以将其分配给在 Erlang shell 中命名的变量：

    4> M = [{attribute,0,module,lager_default_tracer}, ... {tuple,0,[{integer,0,2},{integer,0,1}]}]}]}]}].

    不要忘记添加最后一个句点（又名句号）来完成表达式。

  6. 关闭dbg跟踪：

    5> dbg:stop_clear(). ok

  7. 编译摘要格式：

    6> {ok, _, B} = compile:forms(M, [no_unused_vars, debug_info]). {ok,lager_default_tracer, <<70,79,82,49,0,0,6,164,66,69,65,77,65,116,85,56,0,0,1,9, 0,0,0,23,20,108,...>>}

    该变量现在以二进制形式保存模块B的编译代码。lager_default_tracer

  8. 从存储在的已编译二进制文件中提取抽象代码块B：

    7> {ok,{_,[{abstract_code,{_,AC}}]}} = beam_lib:chunks(B,[abstract_code]). {ok,{lager_default_tracer, [{abstract_code, ... [{clause,0,[{var,0,'Event'}],[],[{call,...}]}]}]}}]}}

    该变量AC现在保存抽象代码。

  9. 使用抽象代码打印lager_default_tracer模块的重构源代码：

    8> io:fwrite("~s~n", [erl_prettypr:format(erl_syntax:form_list(AC))]). -module(lager_default_tracer). -export([info/1, reset_counters/1, table/1, handle/1]). ... handle_(Event) -> gr_counter:update_counter(table(counters), filter, {2, 1}). ok

    这最后一步和之前的一步取自beam_lib文档，在“重建源代码”下。

不出所料，重构的源代码显示了对其他函数的调用，因此如果您想尝试理解重构的代码，则goldrush需要访问goldrush源代码。

于 2017-08-27T13:23:39.550 回答