Re: Blocking protected ops (was: Tasks and C/C++ code)

[Mats Weber <Mats.Weber@elca-matrix.ch>]

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.