dbg模块 [1]¶

实例:

> dbg:start().   % start dbg
> dbg:tracer().  % start a simple tracer process
> dbg:tp(Module, Function, Arity, []).   % specify MFA you are interested in
> dbg:p(all, c).   % trace calls (c) of that MFA for all processes.

... trace here

> dbg:stop_clear().   % stop tracer and clear effect of tp and p calls.

想trace模块中没有导出的函数，请使用tpl:

> dbg:tpl(Module, '_', []).  % all calls in Module
> dbg:tpl(Module, Function, '_', []).   % all calls to Module:Function with any arity.
> dbg:tpl(Module, Function, Arity, []). % all calls to Module:Function/Arity.
> dbg:tpl(M, F, A, [{'_', [], [{return_trace}]}]).   % same as before, but also show return value.

使用dbg:fun2ms来生成函数入参的匹配模式:

1> dbg:fun2ms(fun([M,N]) when N > 3 -> return_trace() end).
[{['$1','$2'],[{'>','$2',3}],[{return_trace}]}]

可以使用dbg:p函数来指定特定的进程:

> dbg:p(all, c).   % trace calls to selected functions by all functions
> dbg:p(new, c).   % trace calls by processes spawned from now on
> dbg:p(Pid, c).   % trace calls by given process
> dbg:p(Pid, [c, m]).  % trace calls and messages of a given process

备注

1.由于trace时产生的日志非常多,通常需要把它放到一个文件汇总后再分析(而不是直接输出到shell中):

生成多个文件保存日志: >dbg:tracer(port,dbg:trace_port(file,{“/log/trace”,wrap,atom_to_list(node())})). 这点也说明了dbg太放纵使用者,一不小心就会产生大量的日志,导致节点异常生产环境中慎用

2.所有的tp,p都是在在dbg:start/0,dbg:trace/0开启后才能起作用的

实例-监听指定进程:

Pid = pid(0, 56, 0).
FileName = "/tmp/dbg.log".
dbg:start().
{ok, IO} = file:open(FileName, [append]).
{ok, TPid} = dbg:tracer(process, {fun dbg:dhandler/2, IO}).
dbg:p(Pid,[m,p]).
dbg:stop().