start at least one async thread in async thread pool

fixes an issue when shell is terminated with an error "Bus error: 10",
on attempt to run rebar shell with verbose logging

priv/templates/escript_rebar.config

@@ -5,7 +5,7 @@
  [{{name}}]}.
 {escript_main_app, {{name}}}.
 {escript_name, {{name}}}.
-{escript_emu_args, "%%! +sbtu +A0\n"}.
+{escript_emu_args, "%%! +sbtu +A1\n"}.
 
 %% Profiles
 {profiles, [{test,

rebar.config

@@ -22,7 +22,7 @@
              ]}.
 
 {escript_name, rebar3}.
-{escript_emu_args, "%%! +sbtu +A0\n"}.
+{escript_emu_args, "%%! +sbtu +A1\n"}.
 %% escript_incl_extra is for internal rebar-private use only.
 %% Do not use outside rebar. Config interface is not stable.
 {escript_incl_extra, [{"relx/priv/templates/*", "_build/default/lib/"},
@@ -78,4 +78,3 @@
                     {add, relx, [{erl_opts, [no_debug_info]}]}]}
             ]}
            ]}.
-

src/rebar3.erl

@@ -54,7 +54,7 @@
 %% ====================================================================
 
 %% @doc For running with:
-%% erl +sbtu +A0 -noinput -mode minimal -boot start_clean -s rebar3 main -extra "$@"
+%% erl +sbtu +A1 -noinput -mode minimal -boot start_clean -s rebar3 main -extra "$@"
 -spec main() -> no_return().
 main() ->
     List = init:get_plain_arguments(),

src/rebar_prv_local_install.erl

@@ -64,7 +64,7 @@ format_error(Reason) ->
 bin_contents(OutputDir) ->
     <<"#!/usr/bin/env sh
 
-erl -pz ", (rebar_utils:to_binary(OutputDir))/binary,"/*/ebin +sbtu +A0 -noshell -boot start_clean -s rebar3 main $REBAR3_ERL_ARGS -extra \"$@\"
+erl -pz ", (rebar_utils:to_binary(OutputDir))/binary,"/*/ebin +sbtu +A1 -noshell -boot start_clean -s rebar3 main $REBAR3_ERL_ARGS -extra \"$@\"
 ">>.
 
 extract_escript(State, ScriptPath) ->