fix sys:get_state/1,2 and sys:replace_state/2,3 when sys suspended

Add two new system callbacks Module:system_get_state/1 and
Module:system_replace_state/2 to allow sys:get_state/1,2 and
sys:replace_state/2,3 to operate correctly even if a process is sys
suspended. Modify gen_server, gen_fsm, and gen_event to support the new
callbacks.

If a callback module does not export these functions, then by default the
Misc value (the same as that passed as the final argument to
sys:handle_system_msg/6, and returned as part of the return value of
sys:get_status/1,2) is treated as the callback module's state.

The previous behaviour of intercepting the system message and passing a
tuple of size 2 as the last argument to sys:handle_system_msg/6 is no
longer supported.

Add tests to verify the correctness of sys:get_state/1,2 and
sys:replace_state/2,3 when processes are sys suspended. Add two tests for
modules that implement special processes, one that exports
system_get_state/1 and system_replace_state/2 and one that doesn't.

Much of the credit for this patch goes to James Fish, who reported the
initial problem and implemented much of the fix.

4 files changed, 94 insertions, 44 deletions

diff --git a/lib/stdlib/src/gen_event.erl b/lib/stdlib/src/gen_event.erl
index 7629e88fbf..d39dd89d3a 100644
--- a/lib/stdlib/src/gen_event.erl
+++ b/lib/stdlib/src/gen_event.erl
@@ -40,6 +40,8 @@
 	 system_continue/3,
 	 system_terminate/4,
 	 system_code_change/4,
+	 system_get_state/1,
+	 system_replace_state/2,
 	 format_status/2]).
 
 -export_type([handler/0, handler_args/0, add_handler_ret/0,
@@ -229,24 +231,6 @@ wake_hib(Parent, ServerName, MSL, Debug) ->
 
 fetch_msg(Parent, ServerName, MSL, Debug, Hib) ->
     receive
-	{system, From, get_state} ->
-	    States = [{Mod,Id,State} || #handler{module=Mod, id=Id, state=State} <- MSL],
-	    sys:handle_system_msg(get_state, From, Parent, ?MODULE, Debug,
-				  {States, [ServerName, MSL, Hib]}, Hib);
-	{system, From, {replace_state, StateFun}} ->
-	    {NMSL, NStates} =
-		lists:unzip([begin
-				 Cur = {Mod,Id,State},
-				 try
-				     NState = {Mod,Id,NS} = StateFun(Cur),
-				     {HS#handler{state=NS}, NState}
-				 catch
-				     _:_ ->
-					 {HS, Cur}
-				 end
-			     end || #handler{module=Mod, id=Id, state=State}=HS <- MSL]),
-	    sys:handle_system_msg(replace_state, From, Parent, ?MODULE, Debug,
-				  {NStates, [ServerName, NMSL, Hib]}, Hib);
 	{system, From, Req} ->
 	    sys:handle_system_msg(Req, From, Parent, ?MODULE, Debug,
 				  [ServerName, MSL, Hib],Hib);
@@ -383,6 +367,23 @@ system_code_change([ServerName, MSL, Hib], Module, OldVsn, Extra) ->
 		    MSL),
     {ok, [ServerName, MSL1, Hib]}.
 
+system_get_state([_ServerName, MSL, _Hib]) ->
+    {ok, [{Mod,Id,State} || #handler{module=Mod, id=Id, state=State} <- MSL]}.
+
+system_replace_state(StateFun, [ServerName, MSL, Hib]) ->
+    {NMSL, NStates} =
+		lists:unzip([begin
+				 Cur = {Mod,Id,State},
+				 try
+				     NState = {Mod,Id,NS} = StateFun(Cur),
+				     {HS#handler{state=NS}, NState}
+				 catch
+				     _:_ ->
+					 {HS, Cur}
+				 end
+			     end || #handler{module=Mod, id=Id, state=State}=HS <- MSL]),
+    {ok, NStates, [ServerName, NMSL, Hib]}.
+
 %%-----------------------------------------------------------------
 %% Format debug messages.  Print them as the call-back module sees
 %% them, not as the real erlang messages.  Use trace for that.
diff --git a/lib/stdlib/src/gen_fsm.erl b/lib/stdlib/src/gen_fsm.erl
index e9654322f1..e914f7d0b2 100644
--- a/lib/stdlib/src/gen_fsm.erl
+++ b/lib/stdlib/src/gen_fsm.erl
@@ -118,6 +118,8 @@
 	 system_continue/3,
 	 system_terminate/4,
 	 system_code_change/4,
+	 system_get_state/1,
+	 system_replace_state/2,
 	 format_status/2]).
 
 -import(error_logger, [format/2]).
@@ -422,17 +424,6 @@ wake_hib(Parent, Name, StateName, StateData, Mod, Debug) ->
 
 decode_msg(Msg,Parent, Name, StateName, StateData, Mod, Time, Debug, Hib) ->
     case Msg of
-	{system, From, get_state} ->
-	    Misc = [Name, StateName, StateData, Mod, Time],
-	    sys:handle_system_msg(get_state, From, Parent, ?MODULE, Debug,
-				  {{StateName, StateData}, Misc}, Hib);
-	{system, From, {replace_state, StateFun}} ->
-	    State = {StateName, StateData},
-	    NState = {NStateName, NStateData} = try StateFun(State)
-						catch _:_ -> State end,
-	    NMisc = [Name, NStateName, NStateData, Mod, Time],
-	    sys:handle_system_msg(replace_state, From, Parent, ?MODULE, Debug,
-				  {NState, NMisc}, Hib);
         {system, From, Req} ->
 	    sys:handle_system_msg(Req, From, Parent, ?MODULE, Debug,
 				  [Name, StateName, StateData, Mod, Time], Hib);
@@ -467,6 +458,13 @@ system_code_change([Name, StateName, StateData, Mod, Time],
 	Else -> Else
     end.
 
+system_get_state([_Name, StateName, StateData, _Mod, _Time]) ->
+    {ok, {StateName, StateData}}.
+
+system_replace_state(StateFun, [Name, StateName, StateData, Mod, Time]) ->
+    Result = {NStateName, NStateData} = StateFun({StateName, StateData}),
+    {ok, Result, [Name, NStateName, NStateData, Mod, Time]}.
+
 %%-----------------------------------------------------------------
 %% Format debug messages.  Print them as the call-back module sees
 %% them, not as the real erlang messages.  Use trace for that.
diff --git a/lib/stdlib/src/gen_server.erl b/lib/stdlib/src/gen_server.erl
index 5f14e48b0a..202a931fae 100644
--- a/lib/stdlib/src/gen_server.erl
+++ b/lib/stdlib/src/gen_server.erl
@@ -98,6 +98,8 @@
 -export([system_continue/3,
 	 system_terminate/4,
 	 system_code_change/4,
+	 system_get_state/1,
+	 system_replace_state/2,
 	 format_status/2]).
 
 %% Internal exports
@@ -372,13 +374,6 @@ wake_hib(Parent, Name, State, Mod, Debug) ->
 
 decode_msg(Msg, Parent, Name, State, Mod, Time, Debug, Hib) ->
     case Msg of
-	{system, From, get_state} ->
-	    sys:handle_system_msg(get_state, From, Parent, ?MODULE, Debug,
-				  {State, [Name, State, Mod, Time]}, Hib);
-	{system, From, {replace_state, StateFun}} ->
-	    NState = try StateFun(State) catch _:_ -> State end,
-	    sys:handle_system_msg(replace_state, From, Parent, ?MODULE, Debug,
-				  {NState, [Name, NState, Mod, Time]}, Hib);
 	{system, From, Req} ->
 	    sys:handle_system_msg(Req, From, Parent, ?MODULE, Debug,
 				  [Name, State, Mod, Time], Hib);
@@ -687,6 +682,13 @@ system_code_change([Name, State, Mod, Time], _Module, OldVsn, Extra) ->
 	Else -> Else
     end.
 
+system_get_state([_Name, State, _Mod, _Time]) ->
+    {ok, State}.
+
+system_replace_state(StateFun, [Name, State, Mod, Time]) ->
+    NState = StateFun(State),
+    {ok, NState, [Name, NState, Mod, Time]}.
+
 %%-----------------------------------------------------------------
 %% Format debug messages.  Print them as the call-back module sees
 %% them, not as the real erlang messages.  Use trace for that.
diff --git a/lib/stdlib/src/sys.erl b/lib/stdlib/src/sys.erl
index 04f8dfb61b..e25cc25f57 100644
--- a/lib/stdlib/src/sys.erl
+++ b/lib/stdlib/src/sys.erl
@@ -102,20 +102,31 @@ get_status(Name, Timeout) -> send_system_msg(Name, get_status, Timeout).
 -spec get_state(Name) -> State when
       Name :: name(),
       State :: term().
-get_state(Name) -> send_system_msg(Name, get_state).
+get_state(Name) ->
+    case send_system_msg(Name, get_state) of
+	{error, Reason} -> error(Reason);
+	State -> State
+    end.
 
 -spec get_state(Name, Timeout) -> State when
       Name :: name(),
       Timeout :: timeout(),
       State :: term().
-get_state(Name, Timeout) -> send_system_msg(Name, get_state, Timeout).
+get_state(Name, Timeout) ->
+    case send_system_msg(Name, get_state, Timeout) of
+	{error, Reason} -> error(Reason);
+	State -> State
+    end.
 
 -spec replace_state(Name, StateFun) -> NewState when
       Name :: name(),
       StateFun :: fun((State :: term()) -> NewState :: term()),
       NewState :: term().
 replace_state(Name, StateFun) ->
-    send_system_msg(Name, {replace_state, StateFun}).
+    case send_system_msg(Name, {replace_state, StateFun}) of
+	{error, Reason} -> error(Reason);
+	State -> State
+    end.
 
 -spec replace_state(Name, StateFun, Timeout) -> NewState when
       Name :: name(),
@@ -123,7 +134,10 @@ replace_state(Name, StateFun) ->
       Timeout :: timeout(),
       NewState :: term().
 replace_state(Name, StateFun, Timeout) ->
-    send_system_msg(Name, {replace_state, StateFun}, Timeout).
+    case send_system_msg(Name, {replace_state, StateFun}, Timeout) of
+	{error, Reason} -> error(Reason);
+	State -> State
+    end.
 
 -spec change_code(Name, Module, OldVsn, Extra) -> 'ok' | {error, Reason} when
       Name :: name(),
@@ -390,10 +404,11 @@ do_cmd(_, suspend, _Parent, _Mod, Debug, Misc) ->
     {suspended, ok, Debug, Misc};
 do_cmd(_, resume, _Parent, _Mod, Debug, Misc) ->
     {running, ok, Debug, Misc};
-do_cmd(SysState, get_state, _Parent, _Mod, Debug, {State, Misc}) ->
-    {SysState, State, Debug, Misc};
-do_cmd(SysState, replace_state, _Parent, _Mod, Debug, {State, Misc}) ->
-    {SysState, State, Debug, Misc};
+do_cmd(SysState, get_state, _Parent, Mod, Debug, Misc) ->
+    {SysState, do_get_state(Mod, Misc), Debug, Misc};
+do_cmd(SysState, {replace_state, StateFun},  _Parent, Mod, Debug, Misc) ->
+    {Res, NMisc} = do_replace_state(StateFun, Mod, Misc),
+    {SysState, Res, Debug, NMisc};
 do_cmd(SysState, get_status, Parent, Mod, Debug, Misc) ->
     Res = get_status(SysState, Parent, Mod, Debug, Misc),
     {SysState, Res, Debug, Misc};
@@ -407,6 +422,40 @@ do_cmd(suspended, {change_code, Module, Vsn, Extra}, _Parent,
 do_cmd(SysState, Other, _Parent, _Mod, Debug, Misc) ->
     {SysState, {error, {unknown_system_msg, Other}}, Debug, Misc}.
 
+do_get_state(Mod, Misc) ->
+    case erlang:function_exported(Mod, system_get_state, 1) of
+	true ->
+	    try
+		{ok, State} = Mod:system_get_state(Misc),
+		State
+	    catch
+		Cl:Exc ->
+		    {error, {callback_failed,{Mod,system_get_state},{Cl,Exc}}}
+	    end;
+	false ->
+	    Misc
+    end.
+
+do_replace_state(StateFun, Mod, Misc) ->
+    case erlang:function_exported(Mod, system_replace_state, 2) of
+	true ->
+	    try
+		{ok, State, NMisc} = Mod:system_replace_state(StateFun, Misc),
+		{State, NMisc}
+	    catch
+		Cl:Exc ->
+		    {{error, {callback_failed,{Mod,system_replace_state},{Cl,Exc}}}, Misc}
+	    end;
+	false ->
+	    try
+		NMisc = StateFun(Misc),
+		{NMisc, NMisc}
+	    catch
+		Cl:Exc ->
+		    {{error, {callback_failed,StateFun,{Cl,Exc}}}, Misc}
+	    end
+    end.
+
 get_status(SysState, Parent, Mod, Debug, Misc) ->
     PDict = get(),
     FmtMisc =