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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: copy constructor for sockets
Date: 23 May 2004 12:21:32 +0100
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tmoran@acm.org writes:

> Remember that a task is a thread of control, not a sequence of
> instructions.  From that viewpoint, your server needs to fire up a
> task/thread, and that thread needs to find out whether it should execute
> the Get or the Put sequence of instructions.  You can pass the server
> socket to the task during the rendezvous, and let the task create a socket
> and do the socket-accept.

Is it really possible to have multiple accept()s? You live and learn!
(I thought you could only have one accept(), which blocks until a
client connect()s and then returns a new socket ... so, with your
design, what is the server doing while the task calls accept()?

I know you can use select() or poll() to block until an accept() would
succeed, is that the idea?

>                            That lets the server get back to waiting for
> calls as quickly as possible, while the task does the Get_Line (which
> could potentially take a while) and calls an appropriate Handle_Get or
> Handle_Post procedure.  You can see an example of this in Smplsrvr (part
> of the free Claw download at www.rrsoftware.com).  You might also want to
> see how AWS does it.
> 
> > Doesn't the ":=" operator to a "deep copy"?
> If the object is Limited, ":=" is illegal.  (That's the case for Claw
> Sockets.) If it's Controlled, then ":=" does a bit pattern copy followed
> by a call on Adjust, which may do nothing, may modify pointers or
> whatever, or may do a deep copy - whatever it wants.  If the object is not
> Controlled, and isn't Limited, then ":=" just does a bitwise copy.

That applies recursively to components, of course (remembering that a
type with limited components has to be limited, of course).

I don't know AdaSockets, but GNAT.Sockets (3.15p) has

   type Socket_Type is private;

which means that assignment is available, and, in the private part,

   type Socket_Type is new Integer;

and in the body (eg)

   procedure Accept_Socket
     (Server  : Socket_Type;
      Socket  : out Socket_Type;
      Address : out Sock_Addr_Type)
   is
      Res : C.int;
      Sin : aliased Sockaddr_In;
      Len : aliased C.int := Sin'Size / 8;

   begin
      Res := C_Accept (C.int (Server), Sin'Address, Len'Access);

      if Res = Failure then
         Raise_Socket_Error (Socket_Errno);
      end if;

      Socket := Socket_Type (Res);

      Address.Addr := To_Inet_Addr (Sin.Sin_Addr);
      Address.Port := Port_Type (Network_To_Port (Sin.Sin_Port));
   end Accept_Socket;

so you can see that it's extremely close to the C accept(2); the
socket is essentially a file descriptor, in Unix terms anyway.

So assignment works (for this binding) as it would in C.

-- 
Simon Wright                               100% Ada, no bugs.