Re: Synchronization Question

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 15 Sep 2009 12:27:16 -0700

Message-ID:

<DURrm.201893$Qg6.129175@newsfe14.iad>

Dave Searles wrote:

Peter Duniho wrote:

On Tue, 15 Sep 2009 01:06:46 -0700, Dave Searles
<searles@hoombah.nurt.bt.uk> wrote:

[...] You could do this:
volatile ArrayList<Integer> intList = Collections.synchronizedList(
new ArrayList<Integer>(10) );
And get the semantics you want, at somewhat higher overhead per
access.

The problem is that you can't apparently make the individual array
cells volatile. I suppose an array of a VolatileInt class (with just
a "public volatile int i;" member) could be used, with again some
significant overhead. Whether that overhead is worse than a clever
strategy for locking, or not, is another question.

I took the liberty of reinserting the elided discussion.

As mentioned elsewhere in this thread, Java has the AtomicIntegerArray, which is what one should use if they do want an integer array with volatile semantics on the individual elements. I think that would be a much better approach than reinventing the wheel, with poor performance at best, and serious bugs at worst (though I admit, an array of your VolatileInt elements probably wouldn't be too awful performance-wise except for when the GC eventually has to dispose of all the memory you used for it :) ).

Your attitude baffles me. Is there nothing one can write that will
satisfy you, or at the very least be left alone rather than criticized
by you?

That didn't like like criticism to me at all. Peter was merely pointing
out that AtomicIntegerArray is part of Java, which provides the
semantics desired, in a tested and optimized manor.

Then Peter goes on to point out one of the (rather obvious) problems
with using something like an array of VolatileInt.

If you can't stand having someone reply to your postings, then usenet is
not the place for you.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>