[infinispan-dev] Avoid Collections.emptySet() / emptyMap() / emptyList

[Galder Zamarreño]

On Oct 22, 2012, at 10:13 AM, Dan Berindei <dan.berindei at gmail.com> wrote:

> On Mon, Oct 22, 2012 at 9:25 AM, Galder Zamarreño <galder at redhat.com> wrote:
> 
> On Oct 19, 2012, at 6:28 PM, Dan Berindei <dan.berindei at gmail.com> wrote:
> 
> > Galder, what JDK are you using?
> 
> java version "1.6.0_35"
> Java(TM) SE Runtime Environment (build 1.6.0_35-b10-428-11M3811)
> Java HotSpot(TM) 64-Bit Server VM (build 20.10-b01-428, mixed mode)
> 
> > OpenJDK 1.7 uses EmptyIterator.EMPTY_ITERATOR since 2007:
> >
> > http://hg.openjdk.java.net/jdk7/jdk7/jdk/annotate/37a05a11f281/src/share/classes/java/util/Collections.java
> 
> Good that the figured out this is non-sense.
> 
> > I don't have JDK 1.6 sources on hand to check, but I don't think it's worth optimizing for such an old version anyway.
> 
> Why not? We support JDK 1.6, so nothing stops them from running it.
> 
> Until we baseline on JDK7 (or 8), I'd leave it in.
> 
> 
> My point was that it is a really big change, and further it imposes a burden on anyone writing code with collections in Infinispan. I'm sure we will spend non-trivial amounts of time during reviews pointing out places there the author should have used InfinispanCollections instead of Collections…

It's part of your job as pull request handler to check for these things, and many other bad practices that can be carried out… I don't see why is this different to other.

What's missing here is a check list of things we should be checking for when we handle pull requests.

I volunteer to do one once I got 2LC out of the way.

> I would be willing to go for it if a benchmark showed a significant increase in performance after the change, but you didn't mention any benchmarks, so I guessed that you didn't see a big difference…

It's doesn't affect performance directly, but indirectly.

It's about memory consumption. If you use less memory to do the same work, less burden on GC, and less time spent doing GC.

> 
> 
> >
> > Cheers
> > Dan
> >
> >
> > On Fri, Oct 19, 2012 at 5:50 PM, Vladimir Blagojevic <vblagoje at redhat.com> wrote:
> > Cool! Did not know about this! Is this original idea or others are
> > already doing this?
> > On 12-10-19 8:31 AM, Galder Zamarreño wrote:
> > > Hi all,
> > >
> > > Re: https://github.com/galderz/infinispan/commit/0609207d13216de81d77ff51dc20652ce270c635
> > >
> > > Please avoid using these JDK methods where possible. I've created alternative versions in InfinispanCollections util class that provide a better implementation.
> > >
> > > The problem with the JDK versions is that even if these collections are immutable, if you wanna iterate them (i.e. for(X : emptySet) ), they'll create a brand new Iterator every time they're looped, and that generates useless garbage.
> > >
> > > The InfinispanCollections versions of emptyX will return a constant singleton iterator which avoids this problem, and avoids the need for client code to check if the collection is empty before looping.
> > >
> > > Cheers,
> > > --
> > > Galder Zamarreño
> > > galder at redhat.com
> > > twitter.com/galderz
> > >
> > > Project Lead, Escalante
> > > http://escalante.io
> > >
> > > Engineer, Infinispan
> > > http://infinispan.org
> > >
> 
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--
Galder Zamarreño
galder at redhat.com
twitter.com/galderz

Project Lead, Escalante
http://escalante.io

Engineer, Infinispan
http://infinispan.org