Reproduction escript for trace/3 wierdness

trace_issue.escript

#!/usr/bin/env escript
%% -*- erlang -*-
%%! -smp enable -sname wtf
main(_) ->
    process_flag(trap_exit, true),
    ToMap = lists:seq(1, 50),
    MapFun = fun() ->
               lists:map(fun(N) -> N end, ToMap)
             end,
    start_runner(MapFun),
    timer:sleep(5000).

start_runner(MapFun) ->
    spawn_link(fun() ->
                  Printer = start_printer(),
                  start_tracer(self(), Printer),
                  measure_memory(MapFun, Printer)
               end).

measure_memory(MapFun, Printer) ->
    Printer ! process_info(self(), garbage_collection_info),
    MapFun(),
    Printer ! process_info(self(), garbage_collection_info).

start_printer() ->
    spawn(fun() -> print_loop() end).

print_loop() ->
    receive
        Elem ->
            io:format("~w\n\n", [Elem]),
            print_loop()
    end.

start_tracer(Runner, Printer) ->
    Tracer = spawn(fun() ->
                           tracer_loop(Printer)
                   end),
    erlang:trace(self(), true, [garbage_collection, {tracer, Tracer}]).

tracer_loop(Printer) ->
    receive
        Elem ->
            Printer ! Elem,
            tracer_loop(Printer)
    end.