kernel: Fix an application terminate deadlock possibility

Could happen if get_child was called during terminate.
io (since it is a group_leader) also causes problems after
get_child was called.

Split up and do it async.

1 files changed, 23 insertions, 15 deletions

diff --git a/lib/kernel/src/application_master.erl b/lib/kernel/src/application_master.erl
index 68f78c6eb8..bc15b5a7de 100644
--- a/lib/kernel/src/application_master.erl
+++ b/lib/kernel/src/application_master.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %% 
-%% Copyright Ericsson AB 1996-2013. All Rights Reserved.
+%% Copyright Ericsson AB 1996-2014. All Rights Reserved.
 %% 
 %% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
@@ -27,7 +27,7 @@
 
 -include("application_master.hrl").
 
--record(state, {child, appl_data, children = [], procs = 0, gleader}).
+-record(state, {child, appl_data, children = [], procs = 0, gleader, req=[]}).
 
 %%-----------------------------------------------------------------
 %% Func: start_link/1
@@ -205,22 +205,25 @@ terminate_loop(Child, State) ->
 
 %%-----------------------------------------------------------------
 %% The Application Master is linked to *all* processes in the group
-%% (application).  
+%% (application).
 %%-----------------------------------------------------------------
 handle_msg({get_child, Tag, From}, State) ->
-    From ! {Tag, get_child_i(State#state.child)},
-    State;
+    get_child_i(State, Tag, From);
 handle_msg({stop, Tag, From}, State) ->
     catch terminate(normal, State),
     From ! {Tag, ok},
     exit(normal);
+handle_msg({child, Ref, GrandChild, Mod}, #state{req=Reqs0}=State) ->
+    {value, {_, Tag, From}, Reqs} = lists:keytake(Ref, 1, Reqs0),
+    From ! {Tag, {GrandChild, Mod}},
+    State#state{req=Reqs};
 handle_msg(_, State) ->
     State.
 
-
-terminate(Reason, State) ->
-    terminate_child(State#state.child, State),
-    kill_children(State#state.children),
+terminate(Reason, State = #state{child=Child, children=Children, req=Reqs}) ->
+    _ = [From ! {Tag, error} || {_, Tag, From} <- Reqs],
+    terminate_child(Child, State),
+    kill_children(Children),
     exit(Reason).
 
 
@@ -342,8 +345,8 @@ start_supervisor(Type, M, A) ->
 
 loop_it(Parent, Child, Mod, AppState) ->
     receive
-	{Parent, get_child} ->
-	    Parent ! {self(), Child, Mod},
+	{Parent, get_child, Ref} ->
+	    Parent ! {child, Ref, Child, Mod},
 	    loop_it(Parent, Child, Mod, AppState);
 	{Parent, terminate} ->
 	    NewAppState = prep_stop(Mod, AppState),
@@ -382,10 +385,15 @@ prep_stop(Mod, AppState) ->
 	    NewAppState
     end.
 
-get_child_i(Child) ->
-    Child ! {self(), get_child},
-    receive
-	{Child, GrandChild, Mod} -> {GrandChild, Mod}
+get_child_i(#state{child=Child, req=Reqs}=State, Tag, From) ->
+    Ref = erlang:make_ref(),
+    case erlang:is_process_alive(Child) of
+	true ->
+	    Child ! {self(), get_child, Ref},
+	    State#state{req=[{Ref, Tag, From}|Reqs]};
+	false ->
+	    From ! {Tag, error},
+	    State
     end.
 
 terminate_child_i(Child, State) ->