I've been trying to process the idea of building java vm in java and with the comments on this and other threads it is starting to make sense, but I have a couple of specific question below. I would appreciate if someone could put in a few words of explanation, perhaps it will help others as well. Here goes...
I can see the argument for the code generator written in Java - it still produces the same machine code, so the fact that it is written in Java does not matter.
I can also see the argument that it is algorithms that matter, not the language in which they are written. At least that algorithms matter more.
Ok, but here are the questions.
First one is of the chicken-vs-egg variety -- as the GC algorithm written in Java executes, won't it generate garbage of its own, and won't it then need to be stopped and the tiny little "real" garbage collector run to clean up after it? I can only see two alternatives -- either it is going to cleanup its own garbage, which would be truly fantastacal... Or it will somehow not generate any garbage, which I think is not realistic for a Java program...
This brings me to the second question. In my experience, writing in Java and writing in C (and therefore thinking in Java and thinking in C) tends to produce very different programs. The languages just lead you in different directions. "Language shapes thought," you know. So, although one can argue that a Java program will ultimately be JITed (or WATed or whatever) to machine code, the program itself will not be written in the same way as a C program would be. Again, this is subjective and I expect people will not always agree with this. But I find that when I write C code, I'm thinking of CPU efficiency, changing strings in-place, and using pointers. Maybe *because* C is so painful, I tend to think of the simplest, most direct way to accomplish what is needed.
However, when writing Java, I find that I think more of correct object abstraction for the problem at hand, code reuse, classes that maintain consistent state. I don't think twice of using a HashMap if it happens to be convinient, or that inheritance will cause extra indirections at runtime.
To summarize (and to get to the question already) - the point is that language shapes thought. In other words, a program designed in Java will naturally tend to be slower then a program designed in C, simply because Java most naturally expresses slower designs then C does. And the question is - does this agree with anyone elses experiences? And if it does, is it a valid argument against using Java for the design and implementation of the VM?
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Regards -dmitry
