Question

我已经打印了所有加载的代码，原因如下 {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，它如下：

(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"}]}]

当我致电lager_default_tracer:table(111)时，它如下：

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

Answer 1

lager_default_tracer模块没有关联的beam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。

如果查看goldrush sources，您会看到它调用标准compile:forms/2进行动态编译。通过跟踪该调用，我们可以使用以下步骤重建lager_default_tracer的源代码，假设您已经克隆了lager source repository并成功编译了它。在某些步骤中，Erlang shell命令的输出太大而无法放在此处，因此这些部分使用省略号缩写。

在已编译的克隆lager repo目录中，运行rebar shell以启动Erlang shell，确保所有必需的目录都在Erlang加载路径中。

在shell中，启用dbg tracing并跟踪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}]}

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

这里，输出缩写为仅显示第一行和最后几行。最后两行是application:ensure_all_started/1的结果。这些行之上的所有内容都是lager_default_tracer模块的abstract format。
将跟踪输出从输出跟踪的第一行中的[{attribute,0,module,lager_default_tracer}一直复制到输出跟踪的最后一行中的{tuple,0,[{integer,0,2},{integer,0,1}]}]}]}]}]。不要在您复制的内容中包含结尾文本[nowarn_unused_vars])。
粘贴复制的数据，将其分配给Erlang shell中名为M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段时间（也就是句号）来完成表达。
关闭dbg跟踪：

5> dbg:stop_clear(). ok
编译抽象格式：

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,...>>}

变量B现在作为二进制文件保存lager_default_tracer模块的编译代码。
从B：
中存储的已编译二进制文件中提取抽象代码块
7> {ok,{_,[{abstract_code,{_,AC}}]}} = beam_lib:chunks(B,[abstract_code]). {ok,{lager_default_tracer, [{abstract_code, ... [{clause,0,[{var,0,'Event'}],[],[{call,...}]}]}]}}]}}

变量AC现在包含抽象代码。
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

最后一步和之前的步骤取自beam_lib documentation，在“重构源代码”下。

不出所料，重建的源代码会显示其他goldrush函数的调用，因此如果您想尝试理解重构的代码，则需要访问goldrush sources。

代码梁文件在哪里？

1 个答案: