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Date: Thu, 15 Jun 2017 14:50:30 -0700 (PDT)
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Subject: Question: Controlled data and user disconnection interaction (Gnoga)
From: Olivier Henley <olivier.henley@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:46956
Date: 2017-06-15T14:50:30-07:00
List-Id: <comp.lang.ada>

FIRST: I know this question should be asked on the Gnoga channel but everyb=
ody there is here anyway + other qualified people so ...

Using Gnoga for a multiplayer game, I have a question which I fail to answe=
r myself because I do not know a) enough about Ada and b) enough about the =
architecture of Gnoga/Simple Components stack.

- note1: A match is two players connected through webRTC.
- note2: To establish a webRTC connection between those two players I have =
to relay some infos to one another, without delay.

This sample code is a subset of what I have done to relay messages from one=
 player to the other. My question is about the eventual outcome of one play=
er disconnecting while Relaying. Let suppose the 'other' player is killing =
its browser.
----------------------------

procedure Relay_Signal (App_Data : in App_Data_Access; Value : String) is
      Other_App_Data : App_Data_Access :=3D Control.Find_Other(App_Data);
begin
      if Other_App_Data /=3D null then
         My_Game.Controller.Relay_Signal(Other_App_Data, Value);
      end if;
end Relay_Signal;

protected Control is
      function Find_Other (App_Data : App_Data_Access) return App_Data_Acce=
ss;
private
      Matchs : Matchs_Vec.Vector;
end Control;

protected body Control is

      function Find_Other (App_Data : App_Data_Access) return App_Data_Acce=
ss is
      begin
         if App_Data.Match_Index_Is_Valid then
            for Player of Matchs.Element(App_Data.Match_Index).Players loop
               if Player /=3D App_Data then
                  return Player;
               end if;
            end loop;
         end if;
         return null;
      end Find_Other;

end Control;

-----------------------------

I suppose that in the worst case: Other_App_Data is found and returned from=
 Find_Other but that other player is disconnected (Other_App_Data becomes i=
nvalid) just before My_Game.Controller.Relay_Signal(Other_App_Data, Value) =
is called. What I think will happen is just an exception thrown when I am m=
anipulating Other_App_Data inside Relay_Signal.

1) Am I right? If so is it OK?
2) Else, why and how should I handle such a case?

Thx,

Olivier