fixnums in the VM

Or, the headless object rides again.

Language-specific VMs often use pseudo-pointers with an immediate “payload” to represent a commonly used subset of numbers, and also “headerless” representations for small but ever-present types like Lisp’s cons cell. The JVM can support fixnums and other headerless objects for the sake of these languages, and even for Java. The idea is to make ordinary object pointers (sometimes called oops) coexist with more specialized formats for headerless objects, which we will call iops and xops. The techniques are mature and well-known, and the overheads (of extra tag checking before pointer usage) can be controlled by optimizations already used widely in JVMs.

We will examine low-level encoding techniques, and investigated how to integrate these concepts into the JVM. Although a language implementor might prefer to try these techniques in the closed environment of a from-scratch, specialized VM, it is probably more profitable in the end to incorporate them into an optimized, mature JIT and GC, such as the Open JDK project. [Read More]

Posted by jrose [JVM] ( March 12, 2008 10:08 PM ) Permalink | Comments[6]

destroy the home schoolers in order to save them

Some of my colleagues have noticed the news flurry about home schooling and the sudden declaration of its illegality by a panel of federal judges in Los Angeles. The formal decision features a spicy stew of judicial threats to parents, in a section entitled “Consequences of Parental Denial of a Legal Education”.

That certainly got my attention and that of many friends, since (dare I now admit?) I've been home schooling my children since 1987. Two have finished with honors at good universities and are now productive taxpayers, two more are now making their way through college, and the rest are ahead of grade level and nicely socialized, thank you. Who knew my wife and I were guilty of Parental Denial of a Legal Education? (Gotta get some of that Legal Education. It must make you as wise as a Judge.) To those of us in the home schooling community, the general consensus is more adequately phrased in a San Francisco Chronicle Op-Ed: “What planet are those judges coming from?” I realize the education of one’s children is a culturally subversive thing to do, but since when is California suddenly shy of cultural deviancy?

One can only wince in wonder at the ideal California those judges are contemplating. The state has an interest in many children’s rights beyond mere education, such as nutrition. Perhaps we should require parents to be certified dieticians before they cook their children’s lunch. Or, let’s just go all the way and eliminate the inconvenient families, by requiring a parental license before the first child is brought to term. That would bring everything nicely under control, and our Wise Judges could rule a utopian, aristocratic Plato’s Republic—which is really a nice place to study, but a terrible home.

In my own home town of San Jose, I just noticed a reasonable Mercury News editorial on the subject. Common sense still rules in San Jose!

I make one key exception to the Merc.’s editorial position: All else being equal, I as a private citizen greatly prefer benign neglect to any form of regulation. But unlike us private citizens, editorial writers and politicians seem to have a professional rule: Never make ringing calls to do nothing. (And the corollary: Never be without a ringing call.) I am thankful that, somehow despite all the political fidgeting, life goes on anyway.

Also, I’m proud to say that the two debaters the Mercury mentions are from our group’s debate club. I think it is not too much to hope that, in their day as judges or other community leaders, they will write better opinions.

In the end, my advice to judges, and even to friendly editorialists and politicians, is: Leave parenting to us parents. It worked when all of us were growing up, and it works now.

Posted by jrose [Personal] ( March 12, 2008 06:48 PM ) Permalink