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, 19 insertions, 18 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.