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From: hreba <hreba@t-online.de>
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Subject: Plugin with controlled variable for initialization.
Date: Wed, 2 Feb 2022 18:21:03 +0100
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For the plugin scheme in my actual program I worked along the 
corresponding gnat example, but while the original works, mine doesn't. 
So I boiled it down to a minimum.

plugin.ads
----------

package Plugin is
    procedure Empty;
end Plugin;

plugin.adb
----------
with Ada.Finalization;
with Ada.Text_IO;

package body Plugin is

    type Life_Controller is new Ada.Finalization.Limited_Controlled with 
null record;
    overriding procedure Initialize (lc: in out Life_Controller);
    overriding procedure Finalize (lc: in out Life_Controller);

    procedure Empty is
    begin
       null;
    end Empty;

    overriding procedure Initialize (lc: in out Life_Controller) is
    begin
       Ada.Text_IO.Put_Line("Hello world!");
    end Initialize;

    overriding procedure Finalize (lc: in out Life_Controller) is
    begin
       Ada.Text_IO.Put_Line("Bye world!");
    end Finalize;

    lc:	Life_Controller;

end Plugin;

main.adb
--------
with System;
with Interfaces.C.Strings;
with Ada.Text_IO;

procedure Main is

    use type System.Address;
    RTLD_LAZY:	constant := 1;
    handle:	System.Address;

    function dlopen (Lib_Name: String; Mode: Interfaces.C.int)
		   return System.Address;
    pragma Import (C, dlopen, "dlopen");

begin
    handle:= dlopen ("../Plugin/lib/libplugin.so" & ASCII.NUL, RTLD_LAZY);
    if handle = System.Null_Address then
       Ada.Text_IO.Put_Line("unable to load plugin");
    end if;
end Main;


Main executes without any output. My understanding is the following:

  - When plugin loading with dlopen fails, I get an error message.
  - Otherwise, the controlled variable lc in plugin.adb comes to life and
    I get an output from the Initialize procedure.

Where is my misconception?
-- 
Frank Hrebabetzky, Kronach	+49 / 9261 / 950 0565