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From: Dennis Hoppe <dennis.hoppe@hoppinet.de>
Newsgroups: comp.lang.ada
Subject: Re: Problems with Ada.Streams.Read (blocking)
Date: Fri, 08 Aug 2008 20:08:43 +0200
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Date: 2008-08-08T20:08:43+02:00
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Hi Adam,


Adam Beneschan wrote:
> I'm not familiar with GNAT.Sockets, but looking at the spec it appears
> that there are a couple routines that might help: Control_Socket which
> lets you specify non-blocking I/O, and Check_Selector which I think
> can be used to query whether data is available, if you give it a
> Timeout of zero.  Anyway, I haven't tried anything and I have no idea
> whether it's appropriate for your problem, but it seems like it might
> help.  If not, my apologies.
> 
>                                   -- Adam


I tried to implement your idea:

with Ada.Text_IO;
with Ada.Streams; use Ada.Streams;
with GNAT.Sockets; use GNAT.Sockets;
use type Ada.Streams.Stream_Element_Count;

procedure Test is
    Client: Socket_Type;
    Address: Sock_Addr_Type;
    Channel: Stream_Access;
    Data   : Ada.Streams.Stream_Element_Array (1 .. 256);
    Offset : Ada.Streams.Stream_Element_Count := 1;
    Request : Request_Type;

begin
    Initialize;
    Create_Socket(Client);
    Address.Addr := Inet_Addr("127.0.0.1");
    Address.Port := 21;
    Connect_Socket (Client, Address);

    Request := (Name => Non_Blocking_IO, Enabled => True);
    Control_Socket (Client, Request);  -- make socket I/O non-blocking
    Channel := Stream (Client);

    declare
       Message : String (1 .. 256);
    begin
       String'Read (Channel, Message);
       Ada.Text_IO.Put_Line (Message);
    end;
end Test;


The code blocks now in line

   Control_Socket (Client, Request);  -- make socket I/O non-blocking

The application crashes with: Segmentation fault. *shrugging*

Maybe Create_Selector is the way to go...


Best regards,
   Dennis