Re: Common sense...

[Simon Wright <simon@pushface.org>]

"chris.danx" <spamoff.danx@ntlworld.com> writes:

> What's the right thing to do in the following scenario concerning
> iterators and lists?
> 
> A list is in use by three iterators, A, B and C.  A is at the
> position preceding B and C, C calls the remove subroutine on that
> node and moves on.  The nodes iterator count which was 2 is
> decreased to 1.  B is the only iterator using that node, but A wants
> to moves to the next position before B exits the node (if B had
> exited the node prior to A calling next, there'd be no problem).
> Where does A go?  Does it go to the node at B or does it go to the
> one after B?
> 
> I'd say A skips the node but I've got to go, Dinners out, and so
> can't explain my thoughts on why until later!

Although the BCs support some concurrency, I think it's a minefield
and you'd be better off saying DON'T DO THAT!

My (limited) experience of actually _using_ the BCs in a concurrent
situation have convinced me that no general purpose solution is going
to support every usage that your users can dream up, so don't try. I
might (depending on user response) consider deprecating[1] the
concurrency support (at least as built into the BC containers, I think
there's some value in reusable Semaphores, Monitors and Locks maybe).

Consider the comparison with file IO (files are a sort of container,
after all).

[1] Should we lobby for "pragma Deprecate" in Ada0Y ?-)