Merge branch 'bjorn/fix-on_load/OTP-12593'

* bjorn/fix-on_load/OTP-12593:
  Update documentation regarding improvements
  Correctly handle multiple load attempts when on_load is pending
  Avoid deadlock when an on_load function makes an external call to the module itself
  code_server: Eliminate unnecessary Tag in handle_call/3
  Reimplement -on_load()
  Refactor erts_finish_loading() and insert_new_code()
  code_SUITE: Make on_load_binary/1 clearer by using merl

1 files changed, 139 insertions, 104 deletions

diff --git a/lib/kernel/src/code_server.erl b/lib/kernel/src/code_server.erl
index 90b2a06c46..6174136507 100644
--- a/lib/kernel/src/code_server.erl
+++ b/lib/kernel/src/code_server.erl
@@ -32,7 +32,12 @@
 
 -import(lists, [foreach/2]).
 
--type on_load_item() :: {reference(),module(),file:name_all(),[pid()]}.
+-type on_load_action() ::
+	fun((term(), state()) -> {'reply',term(),state()} |
+				 {'noreply',state()}).
+
+-type on_load_item() :: {{pid(),reference()},module(),
+			 [{pid(),on_load_action()}]}.
 
 -record(state, {supervisor :: pid(),
 		root :: file:name_all(),
@@ -142,7 +147,7 @@ reply(Pid, Res) ->
 loop(#state{supervisor=Supervisor}=State0) ->
     receive 
 	{code_call, Pid, Req} ->
-	    case handle_call(Req, {Pid, call}, State0) of
+	    case handle_call(Req, Pid, State0) of
 		{reply, Res, State} ->
 		    _ = reply(Pid, Res),
 		    loop(State);
@@ -155,8 +160,8 @@ loop(#state{supervisor=Supervisor}=State0) ->
 	    system_terminate(Reason, Supervisor, [], State0);
 	{system, From, Msg} ->
 	    handle_system_msg(running,Msg, From, Supervisor, State0);
-	{'DOWN',Ref,process,_,Res} ->
-	    State = finish_on_load(Ref, Res, State0),
+	{'DOWN',Ref,process,Pid,Res} ->
+	    State = finish_on_load({Pid,Ref}, Res, State0),
 	    loop(State);
 	_Msg ->
 	    loop(State0)
@@ -225,90 +230,90 @@ system_code_change(State, _Module, _OldVsn, _Extra) ->
 %% The gen_server call back functions.
 %%
 
-handle_call({stick_dir,Dir}, {_From,_Tag}, S) ->
+handle_call({stick_dir,Dir}, _From, S) ->
     {reply,stick_dir(Dir, true, S),S};
 
-handle_call({unstick_dir,Dir}, {_From,_Tag}, S) ->
+handle_call({unstick_dir,Dir}, _From, S) ->
     {reply,stick_dir(Dir, false, S),S};
 
-handle_call({stick_mod,Mod}, {_From,_Tag}, S) ->
+handle_call({stick_mod,Mod}, _From, S) ->
     {reply,stick_mod(Mod, true, S),S};
 
-handle_call({unstick_mod,Mod}, {_From,_Tag}, S) ->
+handle_call({unstick_mod,Mod}, _From, S) ->
     {reply,stick_mod(Mod, false, S),S};
 
-handle_call({dir,Dir}, {_From,_Tag}, S) ->
+handle_call({dir,Dir}, _From, S) ->
     Root = S#state.root,
     Resp = do_dir(Root,Dir,S#state.namedb),
     {reply,Resp,S};
 
-handle_call({load_file,Mod}, Caller, St) when is_atom(Mod) ->
-    load_file(Mod, Caller, St);
+handle_call({load_file,Mod}, From, St) when is_atom(Mod) ->
+    load_file(Mod, From, St);
 
-handle_call({add_path,Where,Dir0}, {_From,_Tag},
+handle_call({add_path,Where,Dir0}, _From,
 	    #state{namedb=Namedb,path=Path0}=S) ->
     {Resp,Path} = add_path(Where, Dir0, Path0, Namedb),
     {reply,Resp,S#state{path=Path}};
 
-handle_call({add_paths,Where,Dirs0}, {_From,_Tag},
+handle_call({add_paths,Where,Dirs0}, _From,
 	    #state{namedb=Namedb,path=Path0}=S) ->
     {Resp,Path} = add_paths(Where, Dirs0, Path0, Namedb),
     {reply,Resp,S#state{path=Path}};
 
-handle_call({set_path,PathList}, {_From,_Tag},
+handle_call({set_path,PathList}, _From,
 	    #state{path=Path0,namedb=Namedb}=S) ->
     {Resp,Path,NewDb} = set_path(PathList, Path0, Namedb),
     {reply,Resp,S#state{path=Path,namedb=NewDb}};
 
-handle_call({del_path,Name}, {_From,_Tag},
+handle_call({del_path,Name}, _From,
 	    #state{path=Path0,namedb=Namedb}=S) ->
     {Resp,Path} = del_path(Name, Path0, Namedb),
     {reply,Resp,S#state{path=Path}};
 
-handle_call({replace_path,Name,Dir}, {_From,_Tag},
+handle_call({replace_path,Name,Dir}, _From,
 	    #state{path=Path0,namedb=Namedb}=S) ->
     {Resp,Path} = replace_path(Name, Dir, Path0, Namedb),
     {reply,Resp,S#state{path=Path}};
 
-handle_call(get_path, {_From,_Tag}, S) ->
+handle_call(get_path, _From, S) ->
     {reply,S#state.path,S};
 
 %% Messages to load, delete and purge modules/files.
-handle_call({load_abs,File,Mod}, Caller, S) when is_atom(Mod) ->
+handle_call({load_abs,File,Mod}, From, S) when is_atom(Mod) ->
     case modp(File) of
 	false ->
 	    {reply,{error,badarg},S};
 	true ->
-	    load_abs(File, Mod, Caller, S)
+	    load_abs(File, Mod, From, S)
     end;
 
-handle_call({load_binary,Mod,File,Bin}, Caller, S) when is_atom(Mod) ->
-    do_load_binary(Mod, File, Bin, Caller, S);
+handle_call({load_binary,Mod,File,Bin}, From, S) when is_atom(Mod) ->
+    do_load_binary(Mod, File, Bin, From, S);
 
-handle_call({load_native_partial,Mod,Bin}, {_From,_Tag}, S) ->
+handle_call({load_native_partial,Mod,Bin}, _From, S) ->
     Architecture = erlang:system_info(hipe_architecture),
     Result = (catch hipe_unified_loader:load(Mod, Bin, Architecture)),
     Status = hipe_result_to_status(Result, S),
     {reply,Status,S};
 
-handle_call({load_native_sticky,Mod,Bin,WholeModule}, {_From,_Tag}, S) ->
+handle_call({load_native_sticky,Mod,Bin,WholeModule}, _From, S) ->
     Architecture = erlang:system_info(hipe_architecture),
     Result = (catch hipe_unified_loader:load_module(Mod, Bin, WholeModule,
                                                     Architecture)),
     Status = hipe_result_to_status(Result, S),
     {reply,Status,S};
 
-handle_call({ensure_loaded,Mod}, Caller, St) when is_atom(Mod) ->
+handle_call({ensure_loaded,Mod}, From, St) when is_atom(Mod) ->
     case erlang:module_loaded(Mod) of
 	true ->
 	    {reply,{module,Mod},St};
 	false when St#state.mode =:= interactive ->
-	    load_file(Mod, Caller, St);
+	    ensure_loaded(Mod, From, St);
 	false ->
 	    {reply,{error,embedded},St}
     end;
 
-handle_call({delete,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
+handle_call({delete,Mod}, _From, St) when is_atom(Mod) ->
     case catch erlang:delete_module(Mod) of
 	true ->
 	    ets:delete(St#state.moddb, Mod),
@@ -317,48 +322,50 @@ handle_call({delete,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
 	    {reply,false,St}
     end;
 
-handle_call({purge,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
+handle_call({purge,Mod}, _From, St) when is_atom(Mod) ->
     {reply,do_purge(Mod),St};
 
-handle_call({soft_purge,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
+handle_call({soft_purge,Mod}, _From, St) when is_atom(Mod) ->
     {reply,do_soft_purge(Mod),St};
 
-handle_call({is_loaded,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
+handle_call({is_loaded,Mod}, _From, St) when is_atom(Mod) ->
     {reply,is_loaded(Mod, St#state.moddb),St};
 
-handle_call(all_loaded, {_From,_Tag}, S) ->
+handle_call(all_loaded, _From, S) ->
     Db = S#state.moddb,
     {reply,all_loaded(Db),S};
 
-handle_call({get_object_code,Mod}, {_From,_Tag}, St) when is_atom(Mod) ->
+handle_call({get_object_code,Mod}, _From, St) when is_atom(Mod) ->
     Path = St#state.path,
     case mod_to_bin(Path, Mod) of
 	{_,Bin,FName} -> {reply,{Mod,Bin,FName},St};
 	Error -> {reply,Error,St}
     end;
 
-handle_call({is_sticky, Mod}, {_From,_Tag}, S) ->
+handle_call({is_sticky, Mod}, _From, S) ->
     Db = S#state.moddb,
     {reply, is_sticky(Mod,Db), S};
 
-handle_call(stop,{_From,_Tag}, S) ->
+handle_call(stop,_From, S) ->
     {stop,normal,stopped,S};
 
-handle_call({set_primary_archive, File, ArchiveBin, FileInfo, ParserFun}, {_From,_Tag}, S=#state{mode=Mode}) ->
-    case erl_prim_loader:set_primary_archive(File, ArchiveBin, FileInfo, ParserFun) of
+handle_call({set_primary_archive, File, ArchiveBin, FileInfo, ParserFun},
+	    _From, S=#state{mode=Mode}) ->
+    case erl_prim_loader:set_primary_archive(File, ArchiveBin, FileInfo,
+					     ParserFun) of
 	{ok, Files} ->
 	    {reply, {ok, Mode, Files}, S};
 	{error, _Reason} = Error ->
 	    {reply, Error, S}
     end;
 
-handle_call(get_mode, {_From,_Tag}, S=#state{mode=Mode}) ->
+handle_call(get_mode, _From, S=#state{mode=Mode}) ->
     {reply, Mode, S};
 
-handle_call({finish_loading,Prepared,EnsureLoaded}, {_,_}, S) ->
+handle_call({finish_loading,Prepared,EnsureLoaded}, _From, S) ->
     {reply,finish_loading(Prepared, EnsureLoaded, S),S};
 
-handle_call(Other,{_From,_Tag}, S) ->			
+handle_call(Other,_From, S) ->
     error_msg(" ** Codeserver*** ignoring ~w~n ",[Other]),
     {noreply,S}.
 
@@ -1054,14 +1061,14 @@ add_paths(Where,[Dir|Tail],Path,NameDb) ->
 add_paths(_,_,Path,_) ->
     {ok,Path}.
 
-do_load_binary(Module, File, Binary, Caller, St) ->
+do_load_binary(Module, File, Binary, From, St) ->
     case modp(File) andalso is_binary(Binary) of
 	true ->
 	    case erlang:module_loaded(Module) of
 		true -> do_purge(Module);
 		false -> ok
 	    end,
-	    try_load_module(File, Module, Binary, Caller, St);
+	    try_load_module(File, Module, Binary, From, St);
 	false ->
 	    {reply,{error,badarg},St}
     end.
@@ -1070,63 +1077,61 @@ modp(Atom) when is_atom(Atom) -> true;
 modp(List) when is_list(List) -> int_list(List);
 modp(_)                       -> false.
 
-load_abs(File, Mod, Caller, St) ->
+load_abs(File, Mod, From, St) ->
     Ext = objfile_extension(),
     FileName0 = lists:concat([File, Ext]),
     FileName = absname(FileName0),
     case erl_prim_loader:get_file(FileName) of
 	{ok,Bin,_} ->
-	    try_load_module(FileName, Mod, Bin, Caller, St);
+	    try_load_module(FileName, Mod, Bin, From, St);
 	error ->
 	    {reply,{error,nofile},St}
     end.
 
-try_load_module(File, Mod, Bin, {From,_}=Caller, St0) ->
-    case pending_on_load(Mod, From, St0) of
-	no ->
-	    try_load_module_1(File, Mod, Bin, Caller, St0);
-	{yes,St} ->
-	    {noreply,St}
-    end.
+try_load_module(File, Mod, Bin, From, St) ->
+    Action = fun(_, S) ->
+		     try_load_module_1(File, Mod, Bin, From, S)
+	     end,
+    handle_pending_on_load(Action, Mod, From, St).
 
-try_load_module_1(File, Mod, Bin, Caller, #state{moddb=Db}=St) ->
+try_load_module_1(File, Mod, Bin, From, #state{moddb=Db}=St) ->
     case is_sticky(Mod, Db) of
 	true ->                         %% Sticky file reject the load
 	    error_msg("Can't load module '~w' that resides in sticky dir\n",[Mod]),
 	    {reply,{error,sticky_directory},St};
 	false ->
             Architecture = erlang:system_info(hipe_architecture),
-            try_load_module_2(File, Mod, Bin, Caller, Architecture, St)
+            try_load_module_2(File, Mod, Bin, From, Architecture, St)
     end.
 
-try_load_module_2(File, Mod, Bin, Caller, undefined, St) ->
-    try_load_module_3(File, Mod, Bin, Caller, undefined, St);
-try_load_module_2(File, Mod, Bin, Caller, Architecture,
+try_load_module_2(File, Mod, Bin, From, undefined, St) ->
+    try_load_module_3(File, Mod, Bin, From, undefined, St);
+try_load_module_2(File, Mod, Bin, From, Architecture,
                   #state{moddb=Db}=St) ->
     case catch hipe_unified_loader:load_native_code(Mod, Bin, Architecture) of
         {module,Mod} = Module ->
 	    ets:insert(Db, [{{native,Mod},true},{Mod,File}]),
             {reply,Module,St};
         no_native ->
-            try_load_module_3(File, Mod, Bin, Caller, Architecture, St);
+            try_load_module_3(File, Mod, Bin, From, Architecture, St);
         Error ->
             error_msg("Native loading of ~ts failed: ~p\n", [File,Error]),
             {reply,ok,St}
     end.
 
-try_load_module_3(File, Mod, Bin, Caller, Architecture,
-                  #state{moddb=Db}=St) ->
-    case erlang:load_module(Mod, Bin) of
-        {module,Mod} = Module ->
-            ets:insert(Db, {Mod,File}),
-            post_beam_load([Mod], Architecture, St),
-            {reply,Module,St};
-        {error,on_load} ->
-            handle_on_load(Mod, File, Caller, St);
-        {error,What} = Error ->
-            error_msg("Loading of ~ts failed: ~p\n", [File, What]),
-            {reply,Error,St}
-    end.
+try_load_module_3(File, Mod, Bin, From, Architecture, St0) ->
+    Action = fun({module,_}=Module, #state{moddb=Db}=S) ->
+		     ets:insert(Db, {Mod,File}),
+		     post_beam_load([Mod], Architecture, S),
+		     {reply,Module,S};
+		({error,on_load_failure}=Error, S) ->
+		     {reply,Error,S};
+		({error,What}=Error, S) ->
+		     error_msg("Loading of ~ts failed: ~p\n", [File, What]),
+		     {reply,Error,S}
+	     end,
+    Res = erlang:load_module(Mod, Bin),
+    handle_on_load(Res, Action, Mod, From, St0).
 
 hipe_result_to_status(Result, #state{moddb=Db}) ->
     case Result of
@@ -1151,18 +1156,29 @@ int_list([H|T]) when is_integer(H) -> int_list(T);
 int_list([_|_])                    -> false;
 int_list([])                       -> true.
 
-load_file(Mod, {From,_}=Caller, St0) ->
-    case pending_on_load(Mod, From, St0) of
-	no -> load_file_1(Mod, Caller, St0);
-	{yes,St} -> {noreply,St}
-    end.
-
-load_file_1(Mod, Caller, #state{path=Path}=St) ->
+ensure_loaded(Mod, From, St0) ->
+    Action = fun(_, S) ->
+		     case erlang:module_loaded(Mod) of
+			 true ->
+			     {reply,{module,Mod},S};
+			 false ->
+			     load_file_1(Mod, From, S)
+		     end
+	     end,
+    handle_pending_on_load(Action, Mod, From, St0).
+
+load_file(Mod, From, St0) ->
+    Action = fun(_, S) ->
+		     load_file_1(Mod, From, S)
+	     end,
+    handle_pending_on_load(Action, Mod, From, St0).
+
+load_file_1(Mod, From, #state{path=Path}=St) ->
     case mod_to_bin(Path, Mod) of
 	error ->
 	    {reply,{error,nofile},St};
 	{Mod,Binary,File} ->
-	    try_load_module_1(File, Mod, Binary, Caller, St)
+	    try_load_module_1(File, Mod, Binary, From, St)
     end.
 
 mod_to_bin([Dir|Tail], Mod) ->
@@ -1305,59 +1321,78 @@ run([F|Fs], Data0) ->
 %% The on_load functionality.
 %% -------------------------------------------------------
 
-handle_on_load(Mod, File, {From,_}, #state{on_load=OnLoad0}=St0) ->
+handle_on_load({error,on_load}, Action, Mod, From, St0) ->
+    #state{on_load=OnLoad0} = St0,
     Fun = fun() ->
 		  Res = erlang:call_on_load_function(Mod),
 		  exit(Res)
 	  end,
-    {_,Ref} = spawn_monitor(Fun),
-    OnLoad = [{Ref,Mod,File,[From]}|OnLoad0],
+    PidRef = spawn_monitor(Fun),
+    PidAction = {From,Action},
+    OnLoad = [{PidRef,Mod,[PidAction]}|OnLoad0],
     St = St0#state{on_load=OnLoad},
-    {noreply,St}.
+    {noreply,St};
+handle_on_load(Res, Action, _, _, St) ->
+    Action(Res, St).
 
-pending_on_load(_, _, #state{on_load=[]}) ->
-    no;
-pending_on_load(Mod, From, #state{on_load=OnLoad0}=St) ->
-    case lists:keymember(Mod, 2, OnLoad0) of
+handle_pending_on_load(Action, Mod, From, #state{on_load=OnLoad0}=St) ->
+    case lists:keyfind(Mod, 2, OnLoad0) of
 	false ->
-	    no;
-	true ->
-	    OnLoad = pending_on_load_1(Mod, From, OnLoad0),
-	    {yes,St#state{on_load=OnLoad}}
+	    Action(ok, St);
+	{{From,_Ref},Mod,_Pids} ->
+	    %% The on_load function tried to make an external
+	    %% call to its own module. That would be a deadlock.
+	    %% Fail the call. (The call is probably from error_handler,
+	    %% and it will ignore the actual error reason and cause
+	    %% an undef execption.)
+	    {reply,{error,deadlock},St};
+	{_,_,_} ->
+	    OnLoad = handle_pending_on_load_1(Mod, {From,Action}, OnLoad0),
+	    {noreply,St#state{on_load=OnLoad}}
     end.
 
-pending_on_load_1(Mod, From, [{Ref,Mod,File,Pids}|T]) ->
-    [{Ref,Mod,File,[From|Pids]}|T];
-pending_on_load_1(Mod, From, [H|T]) ->
-    [H|pending_on_load_1(Mod, From, T)];
-pending_on_load_1(_, _, []) -> [].
+handle_pending_on_load_1(Mod, From, [{PidRef,Mod,Pids}|T]) ->
+    [{PidRef,Mod,[From|Pids]}|T];
+handle_pending_on_load_1(Mod, From, [H|T]) ->
+    [H|handle_pending_on_load_1(Mod, From, T)];
+handle_pending_on_load_1(_, _, []) -> [].
 
-finish_on_load(Ref, OnLoadRes, #state{on_load=OnLoad0,moddb=Db}=State) ->
-    case lists:keyfind(Ref, 1, OnLoad0) of
+finish_on_load(PidRef, OnLoadRes, #state{on_load=OnLoad0}=St0) ->
+    case lists:keyfind(PidRef, 1, OnLoad0) of
 	false ->
 	    %% Since this process in general silently ignores messages
 	    %% it doesn't understand, it should also ignore a 'DOWN'
 	    %% message with an unknown reference.
-	    State;
-	{Ref,Mod,File,WaitingPids} ->
-	    finish_on_load_1(Mod, File, OnLoadRes, WaitingPids, Db),
-	    OnLoad = [E || {R,_,_,_}=E <- OnLoad0, R =/= Ref],
-	    State#state{on_load=OnLoad}
+	    St0;
+	{PidRef,Mod,Waiting} ->
+	    St = finish_on_load_1(Mod, OnLoadRes, Waiting, St0),
+	    OnLoad = [E || {R,_,_}=E <- OnLoad0, R =/= PidRef],
+	    St#state{on_load=OnLoad}
     end.
 
-finish_on_load_1(Mod, File, OnLoadRes, WaitingPids, Db) ->
+finish_on_load_1(Mod, OnLoadRes, Waiting, St) ->
     Keep = OnLoadRes =:= ok,
     erlang:finish_after_on_load(Mod, Keep),
     Res = case Keep of
 	      false ->
 		  _ = finish_on_load_report(Mod, OnLoadRes),
+		  _ = erts_code_purger:purge(Mod),
 		  {error,on_load_failure};
 	      true ->
-		  ets:insert(Db, {Mod,File}),
 		  {module,Mod}
 	  end,
-    _ = [reply(Pid, Res) || Pid <- WaitingPids],
-    ok.
+    finish_on_load_2(Waiting, Res, St).
+
+finish_on_load_2([{Pid,Action}|T], Res, St0) ->
+    case Action(Res, St0) of
+	{reply,Rep,St} ->
+	    _ = reply(Pid, Rep),
+	    finish_on_load_2(T, Res, St);
+	{noreply,St} ->
+	    finish_on_load_2(T, Res, St)
+    end;
+finish_on_load_2([], _, St) ->
+    St.
 
 finish_on_load_report(_Mod, Atom) when is_atom(Atom) ->
     %% No error reports for atoms.