Implemented option to specify number of concurrent workers a command may use

5 files changed, 265 insertions, 87 deletions

diff --git a/ebin/rebar.app b/ebin/rebar.app
index bd76ff7..cfd62d0 100644
--- a/ebin/rebar.app
+++ b/ebin/rebar.app
@@ -25,13 +25,16 @@
               rebar_utils,
               getopt ]},
   {registered, []},
-  {applications, [kernel, 
-                  stdlib, 
+  {applications, [kernel,
+                  stdlib,
                   sasl]},
   {env, [
          %% Default log level
          {log_level, error},
 
+         %% Default parallel jobs
+         {jobs, 3},
+
          %% any_dir processing modules
          {any_dir_modules, [
                             rebar_subdirs,
@@ -51,7 +54,7 @@
                                rebar_eunit,
                                rebar_escripter
                               ]},
-                    
+
                     {rel_dir, [
                                rebar_reltool
                               ]}
diff --git a/src/getopt.erl b/src/getopt.erl
index b335f0c..719d4e1 100644
--- a/src/getopt.erl
+++ b/src/getopt.erl
@@ -11,6 +11,9 @@
 -module(getopt).
 -author('juanjo@comellas.org').
 
+-export([parse/2, usage/2]).
+
+
 -define(TAB_LENGTH, 8).
 %% Indentation of the help messages in number of tabs.
 -define(INDENTATION, 3).
@@ -44,8 +47,6 @@
                    Help    :: string() | undefined
                   }.
 
--export([parse/2, usage/2]).
-
 
 -spec parse([option_spec()], string() | [string()]) -> {ok, {[option()], [string()]}} | {error, {Reason :: atom(), Data :: any()}}.
 %%--------------------------------------------------------------------
@@ -68,72 +69,150 @@ parse(OptSpecList, CmdLine) ->
             Error
     end.
 
+
 -spec parse([option_spec()], [option()], [string()], integer(), [string()]) ->
     {ok, {[option()], [string()]}} | {error, {Reason :: atom(), Data:: any()}}.
+%% Process the option terminator.
+parse(OptSpecList, OptAcc, ArgAcc, _ArgPos, ["--" | Tail]) ->
+    % Any argument present after the terminator is not considered an option.
+    {ok, {lists:reverse(append_default_options(OptSpecList, OptAcc)), lists:reverse(ArgAcc, Tail)}};
 %% Process long options.
-parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [[$-, $- | LongName] = OptStr | Tail]) ->
-    {Option, Tail1} = get_option(OptSpecList, OptStr, LongName, ?OPT_LONG, Tail),
-    parse(OptSpecList, [Option | OptAcc], ArgAcc, ArgPos, Tail1);
+parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [[$-, $- | OptArg] = OptStr | Tail]) ->
+    parse_option_long(OptSpecList, OptAcc, ArgAcc, ArgPos, Tail, OptStr, OptArg);
 %% Process short options.
-parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [[$-, ShortName] = OptStr | Tail]) ->
-    {Option, Tail1} = get_option(OptSpecList, OptStr, ShortName, ?OPT_SHORT, Tail),
-    parse(OptSpecList, [Option | OptAcc], ArgAcc, ArgPos, Tail1);
-%% Process multiple short options with no argument.
-parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [[$- | ShortNameList] = OptStr | Tail]) ->
-    NewOptAcc =
-        lists:foldl(
-          fun (ShortName, OptAcc1) ->
-                  [get_option_no_arg(OptSpecList, OptStr, ShortName, ?OPT_SHORT) | OptAcc1]
-          end, OptAcc, ShortNameList),
-    parse(OptSpecList, NewOptAcc, ArgAcc, ArgPos, Tail);
+parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [[$- | OptArg] = OptStr | Tail]) ->
+    parse_option_short(OptSpecList, OptAcc, ArgAcc, ArgPos, Tail, OptStr, OptArg);
 %% Process non-option arguments.
 parse(OptSpecList, OptAcc, ArgAcc, ArgPos, [Arg | Tail]) ->
     case find_non_option_arg(OptSpecList, ArgPos) of
         {value, OptSpec} when ?IS_OPT_SPEC(OptSpec) ->
-            parse(OptSpecList, [convert_option_arg(OptSpec, Arg) | OptAcc], ArgAcc, ArgPos + 1, Tail);
+            parse(OptSpecList, [convert_option_arg(OptSpec, Arg) | OptAcc],
+                  ArgAcc, ArgPos + 1, Tail);
         false ->
             parse(OptSpecList, OptAcc, [Arg | ArgAcc], ArgPos, Tail)
     end;
 parse(OptSpecList, OptAcc, ArgAcc, _ArgPos, []) ->
-    %% Once we have completed gathering the options we add the ones that were
-    %% not present but had default arguments in the specification.
-    {ok, {lists:reverse(append_default_args(OptSpecList, OptAcc)), lists:reverse(ArgAcc)}}.
-
-
--spec get_option([option_spec()], string(), string() | char(), integer(), [string()]) ->
-    {option(), [string()]}.
-%% @doc Retrieve the specification corresponding to an option matching a string
-%%      received on the command line.
-get_option(OptSpecList, OptStr, OptName, FieldPos, Tail) ->
-    case lists:keysearch(OptName, FieldPos, OptSpecList) of
-        {value, {Name, _Short, _Long, ArgSpec, _Help} = OptSpec} ->
+    % Once we have completed gathering the options we add the ones that were
+    % not present but had default arguments in the specification.
+    {ok, {lists:reverse(append_default_options(OptSpecList, OptAcc)), lists:reverse(ArgAcc)}}.
+
+
+
+%% A long option can have the following formats:
+%% --foo      Single option 'foo', no argument
+%% --foo=bar  Single option 'foo', argument "bar"
+%% --foo bar  Single option 'foo', argument "bar"
+-spec parse_option_long([option_spec()], [option()], [string()], integer(), [string()], string(), string()) ->
+    {ok, {[option()], [string()]}} | {error, {Reason :: atom(), Data:: any()}}.
+parse_option_long(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptStr, OptArg) ->
+    case split_assigned_arg(OptArg) of
+        {Long, Arg} ->
+            % Get option that has its argument within the same string
+            % separated by an equal ('=') character (e.g. "--port=1000").
+            parse_option_assigned_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptStr, Long, Arg);
+
+        Long ->
+            case lists:keysearch(Long, ?OPT_LONG, OptSpecList) of
+                {value, {Name, _Short, Long, undefined, _Help}} ->
+                    parse(OptSpecList, [Name | OptAcc], ArgAcc, ArgPos, Args);
+                
+                {value, {_Name, _Short, Long, _ArgSpec, _Help} = OptSpec} ->
+                    % The option argument string is empty, but the option requires
+                    % an argument, so we look into the next string in the list.
+                    parse_option_next_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptSpec);
+                false ->
+                    throw({error, {invalid_option, OptStr}})
+            end
+    end.
+
+
+parse_option_assigned_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptStr, Long, Arg) ->
+    case lists:keysearch(Long, ?OPT_LONG, OptSpecList) of
+        {value, {_Name, _Short, Long, ArgSpec, _Help} = OptSpec} ->
             case ArgSpec of
                 undefined ->
-                    {Name, Tail};
+                    throw({error, {invalid_option_arg, OptStr}});
                 _ ->
-                    case Tail of
-                        [Arg | Tail1] ->
-                            {convert_option_arg(OptSpec, Arg), Tail1};
-                                    [] ->
-                            throw({error, {missing_option_arg, Name}})
-                    end
+                    parse(OptSpecList, [convert_option_arg(OptSpec, Arg) | OptAcc], ArgAcc, ArgPos, Args)
             end;
         false ->
             throw({error, {invalid_option, OptStr}})
     end.
 
--spec get_option_no_arg([option_spec()], string(), string() | char(), integer()) -> option().
-%% @doc Retrieve the specification corresponding to an option that has no
-%%      argument and matches a string received on the command line.
-get_option_no_arg(OptSpecList, OptStr, OptName, FieldPos) ->
-    case lists:keysearch(OptName, FieldPos, OptSpecList) of
-        {value, {Name, _Short, _Long, undefined, _Help}} ->
-            Name;
-        {value, {Name, _Short, _Long, _ArgSpec, _Help}} ->
-            throw({error, {missing_option_arg, Name}});
+
+-spec split_assigned_arg(string()) -> {Name :: string(), Arg :: string()} | string().
+%% @doc Split an option string that may contain and option with its argument
+%%      separated by an equal ('=') character (e.g. "port=1000").
+split_assigned_arg(OptStr) ->
+    split_assigned_arg(OptStr, OptStr, []).
+
+split_assigned_arg(_OptStr, [$= | Tail], Acc) ->
+    {lists:reverse(Acc), Tail};
+split_assigned_arg(OptStr, [Char | Tail], Acc) ->
+    split_assigned_arg(OptStr, Tail, [Char | Acc]);
+split_assigned_arg(OptStr, [], _Acc) ->
+    OptStr.
+
+
+
+
+%% A short option can have the following formats:
+%% -a       Single option 'a', no argument
+%% -a foo   Single option 'a', argument "foo"
+%% -afoo    Single option 'a', argument "foo"
+%% -abc     Multiple options: 'a'; 'b'; 'c'
+%% -bcafoo  Multiple options: 'b'; 'c'; 'a' with argument "foo"
+-spec parse_option_short([option_spec()], [option()], [string()], integer(), [string()], string(), string()) ->
+    {ok, {[option()], [string()]}} | {error, {Reason :: atom(), Data:: any()}}.
+parse_option_short(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptStr, [Short | Arg]) ->
+    case lists:keysearch(Short, ?OPT_SHORT, OptSpecList) of
+        {value, {Name, Short, _Long, undefined, _Help}} ->
+            parse_option_short(OptSpecList, [Name | OptAcc], ArgAcc, ArgPos, Args, OptStr, Arg);
+
+        {value, {_Name, Short, _Long, ArgSpec, _Help} = OptSpec} ->
+            case Arg of
+                [] ->
+                    % The option argument string is empty, but the option requires
+                    % an argument, so we look into the next string in the list.
+                    parse_option_next_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, OptSpec);
+
+                _ ->
+                    case is_valid_arg(ArgSpec, Arg) of
+                        true ->
+                            parse(OptSpecList, [convert_option_arg(OptSpec, Arg) | OptAcc], ArgAcc, ArgPos, Args);
+                        _ ->
+                            parse_option_short(OptSpecList, [convert_option_no_arg(OptSpec) | OptAcc], ArgAcc, ArgPos, Args, OptStr, Arg)
+                    end
+            end;
+
         false ->
             throw({error, {invalid_option, OptStr}})
+    end;
+parse_option_short(OptSpecList, OptAcc, ArgAcc, ArgPos, Args, _OptStr, []) ->
+    parse(OptSpecList, OptAcc, ArgAcc, ArgPos, Args).
+
+
+%% @doc Retrieve the argument for an option from the next string in the list of
+%%      command-line parameters.
+parse_option_next_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, [Arg | Tail] = Args, {Name, _Short, _Long, ArgSpec, _Help} = OptSpec) ->
+    % Special case for booleans: when the next string is an option we assume
+    % the value is 'true'.
+    case (arg_spec_type(ArgSpec) =:= boolean) andalso not is_boolean_arg(Arg) of
+        true ->
+            parse(OptSpecList, [{Name, true} | OptAcc], ArgAcc, ArgPos, Args);
+        _ ->
+            parse(OptSpecList, [convert_option_arg(OptSpec, Arg) | OptAcc], ArgAcc, ArgPos, Tail)
+    end;
+parse_option_next_arg(OptSpecList, OptAcc, ArgAcc, ArgPos, [] = Args, {Name, _Short, _Long, ArgSpec, _Help}) ->
+    % Special case for booleans: when the next string is missing we assume the
+    % value is 'true'.
+    case arg_spec_type(ArgSpec) of
+        boolean ->
+            parse(OptSpecList, [{Name, true} | OptAcc], ArgAcc, ArgPos, Args);
+        _ ->
+            throw({error, {missing_option_arg, Name}})
     end.
+    
 
 -spec find_non_option_arg([option_spec()], integer()) -> {value, option_spec()} | false.
 %% @doc Find the option for the discrete argument in position specified in the
@@ -148,10 +227,10 @@ find_non_option_arg([], _Pos) ->
     false.
 
 
--spec append_default_args([option_spec()], [option()]) -> [option()].
+-spec append_default_options([option_spec()], [option()]) -> [option()].
 %% @doc Appends the default values of the options that are not present.
-append_default_args([{Name, _Short, _Long, {_Type, DefaultArg}, _Help} | Tail], OptAcc) ->
-    append_default_args(Tail,
+append_default_options([{Name, _Short, _Long, {_Type, DefaultArg}, _Help} | Tail], OptAcc) ->
+    append_default_options(Tail,
                case lists:keymember(Name, 1, OptAcc) of
                    false ->
                        [{Name, DefaultArg} | OptAcc];
@@ -159,29 +238,47 @@ append_default_args([{Name, _Short, _Long, {_Type, DefaultArg}, _Help} | Tail],
                        OptAcc
                end);
 %% For options with no default argument.
-append_default_args([_Head | Tail], OptAcc) ->
-    append_default_args(Tail, OptAcc);
-append_default_args([], OptAcc) ->
+append_default_options([_Head | Tail], OptAcc) ->
+    append_default_options(Tail, OptAcc);
+append_default_options([], OptAcc) ->
     OptAcc.
 
 
--spec convert_option_arg(option_spec(), string()) -> [option()].
+-spec convert_option_no_arg(option_spec()) -> option().
+convert_option_no_arg({Name, _Short, _Long, ArgSpec, _Help}) ->
+    case ArgSpec of
+        % Special case for booleans: if there is no argument we assume
+        % the value is 'true'.
+        {boolean, _DefaultValue} ->
+            {Name, true};
+        boolean ->
+            {Name, true};
+        {_Type, DefaultValue} ->
+            {Name, DefaultValue};
+        _ ->
+            throw({error, {missing_option_arg, Name}})
+    end.
+
+
+-spec convert_option_arg(option_spec(), string()) -> option().
 %% @doc Convert the argument passed in the command line to the data type
-%%      indicated byt the argument specification.
+%%      indicated by the argument specification.
 convert_option_arg({Name, _Short, _Long, ArgSpec, _Help}, Arg) ->
     try
-        Converted = case ArgSpec of
-                        {Type, _DefaultArg} ->
-                            to_type(Type, Arg);
-                        Type when is_atom(Type) ->
-                            to_type(Type, Arg)
-                    end,
-        {Name, Converted}
+        {Name, to_type(arg_spec_type(ArgSpec), Arg)}
     catch
         error:_ ->
             throw({error, {invalid_option_arg, {Name, Arg}}})
     end.
 
+
+-spec arg_spec_type(arg_spec()) -> arg_type() | undefined.
+arg_spec_type({Type, _DefaultArg}) ->
+    Type;
+arg_spec_type(Type) when is_atom(Type) ->
+    Type.
+
+
 -spec to_type(atom(), string()) -> arg_value().
 to_type(binary, Arg) ->
     list_to_binary(Arg);
@@ -192,13 +289,60 @@ to_type(integer, Arg) ->
 to_type(float, Arg) ->
     list_to_float(Arg);
 to_type(boolean, Arg) ->
+    is_boolean_arg(Arg);
+to_type(_Type, Arg) ->
+    Arg.
+
+
+% -spec is_valid_option([option_spec()], Opt :: char() | string(), FieldPos :: integer()) -> boolean().
+% is_valid_option(OptSpecList, Opt, FieldPos) ->
+%     case lists:keysearch(Opt, FieldPos, OptSpecList) of
+%         {value, {_Name, _Short, _Long, _ArgSpec, _Help}} ->
+%             true;
+%         _ ->
+%             false
+%     end.
+
+
+-spec is_valid_arg(arg_spec() | arg_type(), string()) -> boolean().
+is_valid_arg({Type, _DefaultArg}, Arg) ->
+    is_valid_arg(Type, Arg);
+is_valid_arg(boolean, Arg) ->
+    is_boolean_arg(Arg);
+is_valid_arg(integer, Arg) ->
+    is_integer_arg(Arg);
+is_valid_arg(float, Arg) ->
+    is_float_arg(Arg);
+is_valid_arg(_Type, _Arg) ->
+    true.
+
+
+-spec is_boolean_arg(string()) -> boolean().
+is_boolean_arg(Arg) ->
     LowerArg = string:to_lower(Arg),
     (LowerArg =:= "true") orelse (LowerArg =:= "t") orelse
     (LowerArg =:= "yes") orelse (LowerArg =:= "y") orelse
-    (LowerArg =:= "on") orelse (LowerArg =:= "enabled");
-to_type(_Type, Arg) ->
-    Arg.
+    (LowerArg =:= "on") orelse (LowerArg =:= "enabled") orelse
+    (LowerArg =:= "1").
+
+
+-spec is_integer_arg(string()) -> boolean().
+is_integer_arg([Head | Tail]) when Head >= $0, Head =< $9 ->
+    is_integer_arg(Tail);
+is_integer_arg([_Head | _Tail]) ->
+    false;
+is_integer_arg([]) ->
+    true.
+
 
+-spec is_float_arg(string()) -> boolean().
+is_float_arg([Head | Tail]) when (Head >= $0 andalso Head =< $9) orelse Head =:= $. ->
+    is_float_arg(Tail);
+is_float_arg([_Head | _Tail]) ->
+    false;
+is_float_arg([]) ->
+    true.
+  
 
 -spec usage([option_spec()], string()) -> ok.
 %%--------------------------------------------------------------------
@@ -222,10 +366,10 @@ usage_cmd_line([{Name, Short, Long, ArgSpec, _Help} | Tail], Acc) ->
         case ArgSpec of
             undefined ->
                 if
-                    %% For options with short form and no argument.
+                    % For options with short form and no argument.
                     Short =/= undefined ->
                         [$\s, $[, $-, Short, $]];
-                    %% For options with only long form and no argument.
+                    % For options with only long form and no argument.
                     Long =/= undefined ->
                         [$\s, $[, $-, $-, Long, $]];
                     true ->
@@ -233,13 +377,13 @@ usage_cmd_line([{Name, Short, Long, ArgSpec, _Help} | Tail], Acc) ->
                 end;
             _ ->
                 if
-                    %% For options with short form and argument.
+                    % For options with short form and argument.
                     Short =/= undefined ->
                         [$\s, $[, $-, Short, $\s, $<, atom_to_list(Name), $>, $]];
-                    %% For options with only long form and argument.
+                    % For options with only long form and argument.
                     Long =/= undefined ->
                         [$\s, $[, $-, $-, Long, $\s, $<, atom_to_list(Name), $>, $]];
-                    %% For options with neither short nor long form and argument.
+                    % For options with neither short nor long form and argument.
                     true ->
                         [$\s, $<, atom_to_list(Name), $>]
                 end
@@ -260,19 +404,19 @@ usage_options([{Name, Short, Long, _ArgSpec, _Help} = OptSpec | Tail], Acc) ->
         case Long of 
             undefined ->
                 case Short of
-                    %% Neither short nor long form (non-option argument).
+                    % Neither short nor long form (non-option argument).
                     undefined ->
                         [$<, atom_to_list(Name), $>];
-                    %% Only short form.
+                    % Only short form.
                     _ ->
                         [$-, Short]
                 end;
             _ ->
                 case Short of
-                    %% Only long form.
+                    % Only long form.
                     undefined ->
                         [$-, $-, Long];
-                    %% Both short and long form.
+                    % Both short and long form.
                     _ ->
                         [$-, Short, $,, $\s, $-, $-, Long]
                 end
@@ -291,9 +435,9 @@ add_option_help({_Name, _Short, _Long, _ArgSpec, Help}, Prefix, Acc) when is_lis
             Tab = lists:duplicate(ceiling(TabSize / ?TAB_LENGTH), $\t),
             [[$\s, $\s, FlatPrefix, Tab, Help, $\n] | Acc];
         _ ->
-            %% The indentation for the option description is 3 tabs (i.e. 24 characters)
-            %% IMPORTANT: Change the number of tabs below if you change the
-            %%            value of the INDENTATION macro.
+            % The indentation for the option description is 3 tabs (i.e. 24 characters)
+            % IMPORTANT: Change the number of tabs below if you change the
+            %            value of the INDENTATION macro.
             [[$\t, $\t, $\t, Help, $\n], [$\s, $\s, FlatPrefix, $\n] | Acc]
     end;
 add_option_help(_Opt, _Prefix, Acc) ->
@@ -305,8 +449,8 @@ add_option_help(_Opt, _Prefix, Acc) ->
 ceiling(X) ->
     T = erlang:trunc(X),
     case (X - T) of
-        %% Neg when Neg < 0 ->
-        %%    T;
+        % Neg when Neg < 0 ->
+        %    T;
         Pos when Pos > 0 ->
             T + 1;
         _ ->
diff --git a/src/rebar_base_compiler.erl b/src/rebar_base_compiler.erl
index e1312a9..8ca0a7b 100644
--- a/src/rebar_base_compiler.erl
+++ b/src/rebar_base_compiler.erl
@@ -46,7 +46,9 @@ run(Config, FirstFiles, RestFiles, CompileFn) ->
         _ ->
             Self = self(),
             F = fun() -> compile_worker(Self, Config, CompileFn) end,
-            Pids = [spawn_monitor(F) || _I <- lists:seq(1,3)],
+            Jobs = rebar_config:get_jobs(),
+            ?DEBUG("Starting ~B compile worker(s)~n", [Jobs]),
+            Pids = [spawn_monitor(F) || _I <- lists:seq(1,Jobs)],
             compile_queue(Pids, RestFiles)
     end.
 
diff --git a/src/rebar_config.erl b/src/rebar_config.erl
index 0ca9b41..1ccf6af 100644
--- a/src/rebar_config.erl
+++ b/src/rebar_config.erl
@@ -31,7 +31,7 @@
          get_all/2,
          set/3,
          set_global/2, get_global/2,
-         is_verbose/0]).
+         is_verbose/0, get_jobs/0]).
 
 -include("rebar.hrl").
 
@@ -83,6 +83,10 @@ set(Config, Key, Value) ->
     Opts = proplists:delete(Key, Config#config.opts),
     Config#config { opts = [{Key, Value} | Opts] }.
 
+set_global(jobs=Key, Value) when is_list(Value) ->
+    set_global(Key,list_to_integer(Value));
+set_global(jobs=Key, Value) when is_integer(Value) ->
+    application:set_env(rebar_global, Key, erlang:max(1,Value));
 set_global(Key, Value) ->
     application:set_env(rebar_global, Key, Value).
 
@@ -102,6 +106,8 @@ is_verbose() ->
             false
     end.
 
+get_jobs() ->
+    get_global(jobs, 3).
 
 %% ===================================================================
 %% Internal functions
diff --git a/src/rebar_core.erl b/src/rebar_core.erl
index e372983..bc58d72 100644
--- a/src/rebar_core.erl
+++ b/src/rebar_core.erl
@@ -82,18 +82,25 @@ parse_args(Args) ->
     case getopt:parse(OptSpecList, Args) of
         {ok, {_Options, []}} ->
             %% no command to run specified
-            getopt:usage(OptSpecList, "rebar"),
+            help(),
             halt(1);
         {ok, {Options, NonOptArgs}} ->
             case proplists:get_bool(help, Options) of
                 true ->
                     %% display help
-                    getopt:usage(OptSpecList, "rebar"),
+                    help(),
                     halt(0);
                 false ->
                     %% Set global variables based on getopt options
                     set_global_flag(Options, verbose),
                     set_global_flag(Options, force),
+                    DefJobs = rebar_config:get_jobs(),
+                    case proplists:get_value(jobs, Options, DefJobs) of
+                        DefJobs ->
+                            ok;
+                        Jobs ->
+                            rebar_config:set_global(jobs, Jobs)
+                    end,
 
                     %% Filter all the flags (i.e. strings of form key=value) from the
                     %% command line arguments. What's left will be the commands to run.
@@ -101,11 +108,10 @@ parse_args(Args) ->
             end;
         {error, {Reason, Data}} ->
             ?ERROR("Error: ~s ~p~n~n", [Reason, Data]),
-            getopt:usage(OptSpecList, "rebar"),
+            help(),
             halt(1)
     end.
 
-
 %%
 %% set global flag based on getopt option boolean value
 %%
@@ -119,6 +125,21 @@ set_global_flag(Options, Flag) ->
     rebar_config:set_global(Flag, Value).
 
 %%
+%% print help/usage string
+%%
+help() ->
+    Jobs = rebar_config:get_jobs(),
+    io:format(
+"
+Usage: rebar [-h] [-v] [-f] [-j <jobs>] [key=value,...] <command,...>
+
+  -h, --help      Show the program options
+  -v, --verbose   Be verbose about what gets done
+  -f, --force     Force
+  -j, --jobs      Number of concurrent workers a command may use. Default: ~B
+", [Jobs]).
+
+%%
 %% options accepted via getopt
 %%
 option_spec_list() ->
@@ -126,7 +147,9 @@ option_spec_list() ->
      %% {Name, ShortOpt, LongOpt, ArgSpec, HelpMsg}
      {help,    $h, "help",    undefined, "Show the program options"},
      {verbose, $v, "verbose", undefined, "Be verbose about what gets done"},
-     {force,   $f, "force",   undefined, "Force"}
+     {force,   $f, "force",   undefined, "Force"},
+     {jobs,    $j, "jobs",    integer,
+      "Number of concurrent workers a command may use."}
     ].
 
 %%