AdRoll / troll

Erlang selective tracking

troll

A set of erlang debugging/tracing tools.

• troll: convenience wrappers for dbg, allowing simple tracing of functions/modules.
• troll_retro: "Retroactive" tracing:
  • Capture calls beginning when a certain condition is met.
  • Print captured trace when another condition obtains.

Build

$ rebar3 compile

Using

(These examples are out-of-date)

1> TF = fun({trace,_,call,{M=lists,F=seq,A=[1,_]}}, _) ->
             start_trace;
           ({trace,_,call,{M=lists,F=seq,A=[2,_]}}, _) ->
             print_trace;
           ({trace,_,call,{M=lists,F=seq,A=[3,_]}}, _) ->
             end_trace;
           ({trace,_,call,{M,F,A}}, _) ->
             end_trace;
           (_,_) ->
             none
        end.
#Fun<erl_eval.43.65746770>

2> troll_retro:start([{lists,seq}],[{some_key,{TF,undefined}}]).
{ok,<0.151.0>}

3> lists:seq(1,2).
[1,2]

4> lists:seq(2,3).
[<0.140.0>] call   lists:seq(2, 3)
[<0.140.0>] return lists:seq(…) -> [1,2]
[<0.140.0>] call   lists:seq(1, 2)
[2,3]

5> lists:seq(3,4).
[<0.140.0>] call   lists:seq(3, 4)
[<0.140.0>] return lists:seq(…) -> [2,3]
[3,4]

6> lists:seq(3,4).
[3,4]

7> lists:seq(2,4).
[2,3,4]

TODO:

• More overload protection, checking message queues of troll_retro gen_server and tracer (perhaps a separate monitoring process?)
• Shut down tracer when no active triggers.
  • undo dbg:tpl
• Performance improvements for shell funs:
  • Detect if supplied fun is an erl_eval fun
  • Try fun2ms
  • Try compiling to dynamic module
  • Warn or require a 'force' option to use shell funs that can't be compiled somehow
• Docs docs docs!
• Manually stop debugging
• Message send/receive functionality (tie together trace to sending/receiving process)