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.

1 files changed, 9 insertions, 7 deletions

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.