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Mark Reinhold Answers Questions on Closures in Java 7

Posted by editor on December 3, 2009 at 5:31 AM PST

Mark Reinhold provided a significant clarification of issues surrounding the surprise announcement that closures will be included in Java 7 in his new blog post Closures for Java: The Q&A. I'm featuring Mark's post in Java Today.

Mark spends some time both defending himself and stating that there is good reason why he ended up being the one to initiate a new proposal for inclusion of closures in Java 7. He says:

At heart I’m an old Lisp

hacker; more specifically, I’m a past teacher and implementor of the Scheme
dialect. Closures are completely natural to me—along with tail
recursion, continuations, and the definition of procedure call in terms
of rename plus goto. (I accept that I’m unusual in this regard.)

Having said that, in all my years at Sun I’ve done my level best to
respect and preserve the “feel of Java,” as James calls it. Java incorporates
some of the great ideas of the Lisp tradition but it is not, and never
will be, a Lisp. So I’ve always been a bit nervous at the prospect of
adding closures to Java. If we do so then we absolutely must preserve
the existing character of Java as a language for “working programmers.”

Well, for me, this builds confidence that this wasn't a sudden, off the cuff, decision by someone who really doesn't understand all the issues involved.

Mark cites the extension of the JDK 7 schedule as being among the reasons why closures returned to the Java 7 agenda. He reiterates the need "to gain good support for writing scalable
parallel programs using bulk-data APIs such as parallel

I have lots of experience developing multithreaded code, but I haven't done a lot of this in Java (most of my multithreading work has been in C and Fortran on Solaris machines). But, knowing that Mark has expertise in the famed Lisp language, as well as Java, makes me feel more comfortable with the idea that Java's current multithreading support is not sufficient.

The protocols for parallel arrays in Java indeed remind me of the Threading Building Blocks (TBB) open source C++ libraries (I was the first community manager for that project); and, though the syntax is very different, I'm also reminded of the OpenMP API for parallel programming in C/C++ and Fortran.

I spent lots of time seemingly talking into the wind on my Intel Software Network Blog (written when I was TBB community manager) -- saying why I believe multithreaded programming will be the REQUIRED mode of programming in the future. The history and current state of computer processors dictates this, IMO.

Take a look at the history of computing: it consists of constant, rapid increases in processing power and speed (see Moore's Law). Up until a few years ago, speed increases were largely achieved by making certain elements of processor cores thinner, thus lessening the required time for signals to traverse the layer of silicon. A few years ago, we reached the point where the number of layers of silicon was in the teens or so. Engineering thinner layers became impractical. Thus, also, ended the historical realm of validity of Moore's Law.

Henceforward, the most practical way to increase the amount of work a single processor could do was to add more cores. Hence, the "Multicore challenge." Going forward, for applications to be faster, they will need to be able to effectively utilize multicore processors and multiprocessor computers. For this to happen, the applications need to be efficiently multithreaded.

I could go on, and I will in future blog posts. For now, I'll close by saying that if closures in Java will significantly enhance Java's capability with respect to developing multithreaded software applications that can efficiently take advantage of today's multicore processors (and tomorrow's 16 and 32 and 64 cores x processors systems), then I think it's an absolute necessity to add closures to Java 7. Right now is when Java needs the capability to efficiently multithread applications. In fact, Java may be a bit behind the curve, compared with C, C++, Fortran, and .NET... That's not good!

In Java Today, Mark Reinhold published Closures for Java: The Q&A:

At Devoxx last month I said that it's
time to add closures to
. That statement, and my follow-up blog entry,
elicited reactions ranging from enthusiastic support to skeptical acceptance
to cynical indifference. It certainly motivated lots of tweets and lots
of questions. In classic Stephen
style I'll attempt here to summarize and answer some of the key
questions I've seen, so far...

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that you're offered with a bunch of standard “ontologies”, that are
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Those things are related to managing relationships among things. A common need that clearly emerges when you extensively use href="">the
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