Various boot procedure improvements

We ensure that all dependent applications are stopped, but also that
dependencies shared by multiple applications (e.g., amqp_client) are
not.

1 files changed, 36 insertions, 0 deletions

diff --git a/src/app_utils.erl b/src/app_utils.erl
index 1231ea586a..d08dfe6a5a 100644
--- a/src/app_utils.erl
+++ b/src/app_utils.erl
@@ -18,6 +18,7 @@
 -export([load_applications/1, start_applications/1, start_applications/2,
          stop_applications/1, stop_applications/2, app_dependency_order/2,
          running_applications/0, wait_for_applications/1, app_dependencies/1]).
+-export([direct_dependencies/1]).
 
 -ifdef(use_specs).
 
@@ -31,6 +32,7 @@
 -spec wait_for_applications([atom()])               -> 'ok'.
 -spec app_dependency_order([atom()], boolean())     -> [digraph:vertex()].
 -spec app_dependencies(atom())                      -> [atom()].
+-spec direct_dependencies(atom())                   -> [atom()].
 
 -endif.
 
@@ -75,6 +77,40 @@ stop_applications(Apps, ErrorHandler) ->
 wait_for_applications(Apps) ->
     [wait_for_application(App) || App <- Apps], ok.
 
+direct_dependencies(Root) ->
+    G = digraph:new(),
+    Loaded = application:loaded_applications(),
+    try
+        [begin
+             case digraph:vertex(G, App) of
+                 false -> digraph:add_vertex(G, App, App);
+                 _     -> ok = throw({graph_error, {vertex, duplicate, App}})
+             end
+         end || {App, _, _} <- Loaded],
+        [digraph:add_edge(G, App, Dep) ||
+                            {App, Deps} <- [{App, app_dependencies(App)} ||
+                                                {App, _Desc, _Vsn} <- Loaded],
+                            Dep <- Deps],
+        Deps = lists:foldl(
+                 fun(E, Acc) ->
+                     {_, _InVertex, OutVertex, _Label} = digraph:edge(G, E),
+                     case is_reachable(G, OutVertex, Root) of
+                         [] -> sets:add_element(OutVertex, Acc);
+                         _  -> Acc
+                     end
+                 end,
+                 sets:from_list([Root]),
+                 digraph:out_edges(G, Root)),
+        sets:to_list(sets:del_element(rabbit, Deps))
+    catch {graph_error, Reason} ->
+        {error, Reason}
+    after
+        true = digraph:delete(G)
+    end.
+
+is_reachable(G, OutVertex, Root) ->
+    digraph_utils:reaching_neighbours([OutVertex], G) -- [Root].
+
 app_dependency_order(RootApps, StripUnreachable) ->
     {ok, G} = rabbit_misc:build_acyclic_graph(
                 fun (App, _Deps) -> [{App, App}] end,