From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,5d05ccde5cefb836
X-Google-Attributes: gid103376,public
From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: Blocking protected ops (was: Tasks and C/C++ code)
Date: 1998/11/27
Message-ID: <365EEAFA.2D636FD2@elca-matrix.ch>#1/1
X-Deja-AN: 416262652
Content-Transfer-Encoding: 7bit
References: <364702E5.F6987321@hiwaay.net> <729ndu$jfo$1@nnrp1.dejanews.com>
 	<72b35b$pll$1@nnrp1.dejanews.com> <87btm52jwl.fsf@zaphod.enst.fr>
 	<3654746F.3C297E56@elca-matrix.ch> <87k90qunxl.fsf@zaphod.enst.fr>
 	<36599BE3.BA30555B@elca-matrix.ch> <3659b3a8.386623@news.pacbell.net>
 	<365AD980.5729FCD8@elca-matrix.ch> 	<EACHUS.98Nov24143823@spectre.mitre.org>
 	<365BE117.59209A5@elca-matrix.ch> <EACHUS.98Nov25183406@spectre.mitre.org>
 <x7vlnkzx7ok.fsf@pogner.demon.co.uk> <73mo00$24ik$1@news.gate.net>
X-Accept-Language: en
Content-Type: text/plain; charset=us-ascii
Organization: ELCA Matrix SA
Mime-Version: 1.0
Reply-To: Mats.Weber@elca-matrix.ch
Newsgroups: comp.lang.ada
Date: 1998-11-27T00:00:00+00:00
List-Id: <comp.lang.ada>

David Botton wrote:
> 
> After all the discussion on this issue, I am not sure how to implement a
> call to gethosbyname any more.
> 
> Would some one post a correct implementation of this and if one can wrap
> gethostbyname in to a protected type so it can be called by multiple task
> instances even if it (gethostbyname) is not thread safe.

An example of how to do it can be found in:

<ftp://cs.nyu.edu//pub/gnat/glade/glade-1.03p.tar.gz>

or copy this code (compiled, not tested):

   protected Semaphore is
      entry Seize;
      entry Release;
   private
      Busy : Boolean := False;
   end Semaphore;

   protected body Semaphore is

      entry Seize when not Busy is
      begin
         Busy := True;
      end;

      entry Release when Busy is
      begin
         Busy := False;
      end;

   end Semaphore;

   function Gethostbyname (Name : in System.Address)
      return System.Address; -- pointer to hostent

   pragma Import(C, Gethostbyname);

   function Protected_Gethostbyname (Name : in System.Address)
      return System.Address is

      Result : System.Address;

   begin
      Semaphore.Seize;
      Result := Gethostbyname(Name);
      Semaphore.Release;
      return Result;
   exception
      when others =>
         Semaphore.Release;
         raise;
   end Protected_Gethostbyname;

it would be nice to put the call to gethostbyname inside a protected
procedure (so that you need only one protected call instead of two), but
this does not seem to be allowed as gethostbyname could be potentially blocking.