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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Aborting requeued entry calls
Date: Sat, 3 Aug 2002 00:34:20 +0200
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Date: 2002-08-03T00:34:20+02:00
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Hi!

I have a problem and a question. Consider the following:

package Test_Abort is
   protected Thing is
      entry Foo_1;
      entry Foo_2;
   end Thing;
end Test_Abort;
------------------------
with Ada.Text_IO;  use Ada.Text_IO;

package body Test_Abort is
   protected body Thing is
      entry Foo_1 when True is
      begin
         Put_Line ("Foo_1 requeues to Foo_2");
         requeue Foo_2; -- w/o abort
      end Foo_1;
      entry Foo_2 when False is
      begin
         null;
      end Foo_2;
   end Thing;
end Test_Abort;
-------------------------
with Test_Abort;   use Test_Abort;
with Ada.Text_IO;  use Ada.Text_IO;

procedure Test is
begin
   select
      delay 1.0;
   then abort
      Thing.Foo_1;
   end select;
   Put_Line ("Why is that abortable?");
end Test;
--------------------------

The problem. From what I read about requeue with no abort I would expect 
that Test should hang forever. Yet GNAT under Windows successfully
aborts Thing.Foo_1 (after it was requeued to Foo_2).

Is that OK?

If yes, then the question, if a requeued entry call may be silently removed 
from the wait queue, how Thing could become aware of that? Let Foo_1 
changes the state of Thing and Foo_2 restores it, then if Foo_2 get 
silently aborted Thing becomes corrupted. Any solution?

Thanks.

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de