On 02/20/2011 04:41 AM, Jonathan M Davis wrote:
On Saturday 19 February 2011 19:12:17 Jonathan M Davis wrote:
On Saturday 19 February 2011 19:01:16 Steven Schveighoffer wrote:
On Sat, 19 Feb 2011 21:55:53 -0500, Jonathan M Davis
<[email protected]>
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.
Actually, now that I think about it, we're probably going to want a template of
some kind in Phobos which wraps an unsynchronized class with a synchronized one.
There are going to be plenty of cases where it would be nice to have an
unsynchronized class made synchronized (a prime example would be a container
class), and it would be annoying to have to keep creating your own wrappers
every time that you want to do that.
I have not had a look at D's threading implementation, but from what I read I
thought what you describe precisely was the whole point of unshared-by-default
and the 'shared' keyword. Eg I thought something like:
class Foo {...}
shared foo = new Foo();
would do what you write above. Else, what does 'shared' mean?
Denis
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