Merge pull request #316 from talentdeficit/rebar_shell_314

fix for #314 (rebar shell somehow blocks using io:format in gen_server handle_call)

src/rebar_shell.erl

@@ -41,10 +41,20 @@
 
 shell(_Config, _AppFile) ->
     true = code:add_pathz(rebar_utils:ebin_dir()),
+    %% scan all processes for any with references to the old user and save them to
+    %% update later
+    NeedsUpdate = [Pid || Pid <- erlang:processes(),
+        proplists:get_value(group_leader, erlang:process_info(Pid)) == whereis(user)
+    ],
     %% terminate the current user
     ok = supervisor:terminate_child(kernel_sup, user),
     %% start a new shell (this also starts a new user under the correct group)
-    user_drv:start(),
+    _ = user_drv:start(),
+    %% wait until user_drv and user have been registered (max 3 seconds)
+    ok = wait_until_user_started(3000),
+    %% set any process that had a reference to the old user's group leader to the
+    %% new user process
+    _ = [erlang:group_leader(whereis(user), Pid) || Pid <- NeedsUpdate],
     %% enable error_logger's tty output
     ok = error_logger:swap_handler(tty),
     %% disable the simple error_logger (which may have been added multiple
@@ -56,9 +66,10 @@ shell(_Config, _AppFile) ->
 
 info(help, shell) ->
     ?CONSOLE(
-       "Start a shell with project and deps preloaded similar to~n"
-       "'erl -pa ebin -pa deps/*/ebin'.~n",
-       []).
+        "Start a shell with project and deps preloaded similar to~n"
+        "'erl -pa ebin -pa deps/*/ebin'.~n",
+        []
+    ).
 
 remove_error_handler(0) ->
     ?WARN("Unable to remove simple error_logger handler~n", []);
@@ -66,4 +77,15 @@ remove_error_handler(N) ->
     case gen_event:delete_handler(error_logger, error_logger, []) of
         {error, module_not_found} -> ok;
         {error_logger, _} -> remove_error_handler(N-1)
+    end.
+
+%% Timeout is a period to wait before giving up
+wait_until_user_started(0) ->
+    ?ABORT("Timeout exceeded waiting for `user` to register itself~n", []),
+    erlang:error(timeout);
+wait_until_user_started(Timeout) ->
+    case whereis(user) of
+        %% if user is not yet registered wait a tenth of a second and try again
+        undefined -> timer:sleep(100), wait_until_user_started(Timeout - 100);
+        _ -> ok
     end.