shared/unshared classes

[Jonathan M Davis]

On Saturday 19 February 2011 19:01:16 Steven Schveighoffer wrote:
> On Sat, 19 Feb 2011 21:55:53 -0500, Jonathan M Davis <jmdavisProg at gmx.com>
> 
> wrote:
> > On Saturday 19 February 2011 18:26:25 Steven Schveighoffer wrote:
> >> I was working on an I/O library that I plan to use in development, and
> >> possibly submit to phobos, and I thought of this case.
> >> 
> >> A standard file can be shared or unshared.  In C, since there is no
> >> notion
> >> of shared/unshared, everything is shared.  So any writes/reads from a
> >> FILE
> >> * lock the object.
> >> 
> >> But in D, we can avoid those locks when the file is unshared.  However,
> >> this means I have to write two pretty much identical functions for each
> >> call.
> >> 
> >> Is there an expected way to do this?  I've really avoided doing anything
> >> with shared or threads since the new concurrency model came out, but
> >> with
> >> I/O, I'll have to deal with it.
> >> 
> >> I think a logical thing to do would be to have the shared version of the
> >> function call the unshared version after locking the object.  Is that a
> >> good idea?  Is the correct way to do this to mark the shared function
> >> synchronized, and then cast 'this' to unshared to call the other
> >> function?  Does this automatically happen with shared functions?
> > 
> > I would point out that per TDPL, either an entire class is synchronized
> > or none
> > of it is. You don't synchronize individual functions. Now, I don' think
> > that
> > that's the way that it's implemented at the moment, but that's the
> > eventual
> > situation as I understand it. So, your class shouldn't have a mixture of
> > synchronized or unsynchronized. According to TDPL, it's illegal.
> 
> OK, I kind of remember that now.  So that means, I need to create two
> identical hierarchies, a synchronized one and a non-synchronized one?
> 
> I think what I'll do for now is write the non-synchronized versions, and
> then see about maybe automating the synchronized parts.

I'd have to study up on it more to know what the best way to handle it is (I've 
generally avoided dealing with shared), but what you'd probably end up doing is 
creating a wrapper class which was synchronized. However, you might be able to 
get it to just automatically use the right one (unsynchronized for unshared and 
synchronized for shared) if you use templates.

- Jonathan M Davis