Re: copy constructor for sockets

[Simon Wright <simon@pushface.org>]

"Andrew Carroll" <andrew@carroll-tech.net> writes:

> I am wondering if it is possible to write a copy constructor for a
> socket.
> I did not see one in AdaSockets however I have never written a "copy
> constructor" in Ada so I probably wouldn't know what to look for.
> 
> Maybe it violates some standard for socket communication to have a
> copy constructor for a socket?

You have to decide what you want your copy to do!

If you just want to pass the socket around, a plain copy will do
fine. But of course you need to decide what the semantics are.

Copying where one copy is used for read & the other for write is fine,
sockets are like that.

But if you have copies where each is used for reading or writing you
have application-level protocol problems you have to decide:

* is it the same write socket? (ie, the guy at the other end is still
  there and you have two writers): then you'd better be sure your
  sockets are thread-safe (VxWorks stock ones aren't, to my surprise,
  so a single large send(2) can get split). Or you could ensure
  exclusive access with a mutex of some sort.

* is it the same read socket? (ie, only one guy at the other end, you
  are supplying multiple read tasks): better be sure you can split the
  input stream at logical record boundaries.

* do you want a new stream to a new remote process? then it's all got
  _much_ more complicated.

And it'll be a matter of application policy, far too specific to
delegate to a low-level socket abstraction; you'd need to make your
own higher-level abstraction.

-- 
Simon Wright                               100% Ada, no bugs.