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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Suspicious reentrant semaphore
Date: Fri, 02 May 2003 09:28:09 +0200
Organization: At home
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Date: 2003-05-02T09:28:09+02:00
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Jano wrote:

> Dmitry A. Kazakov dice...
>> The requeue statement does the trick in case you want to use a parameter
>> value in a barrier. You could add one more private entry and requeue to
>> it if the task is not the owner:
> 
> Dmitry: I love this suggestion specially because is the first time I'm
> going to employ requeue (never before I faced the necessity).

It is one of the most interesting things added to Ada 95!

> Here is the new version of my package. I've also slightly changed the
> release logic to obtain exceptions instead of deadlocks in case of wrong
> use:

You can also get rid of the task-id parameter, as Randy Brukardt has 
suggested. Sort of:

entry P when true is
begin
   if Owner = P'Caller then
      In_use := In_use + 1;
   else
      requeue Safe_P with abort;
   end if;
end P;
 
entry Safe_P when In_use = 0 is
begin
   Owner := Safe_P'Caller;
   In_use := 1;
end Safe_P;
 
procedure V is
begin
   if Owner /= Current_Task then
      raise Use_error;
   else
      In_use:= In_use - 1;
      if In_use = 0 then
         Owner := Null_task_id;
      end if;
   end if;
end V;

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