问题
Java is a beautifully crafted OO language but the first thing I noticed is how slow it is (compared to C++). This is probably because it has to go through another layer of translation (the VM) instead of running directly in the CPU's native microcode.
My question: Do you know of any attempts to create Java-specific CPU's that run Java natively without requiring the software-implemented VM?
回答1:
Sun designed the picoJava processor about 10 years ago, but it never went anywhere - there was no market for it at the time, and modern VMs render the concept pretty pointless.
Then there's the fledgling ARM Jazelle architecture.
回答2:
The only reference I found so far to this conundrum is the following article:
http://www.theserverside.com/discussions/thread.tss?thread_id=59958
While I was initially interested in first knowing whether there are Java-CPU's and what they are, this thread sheds some light on why I haven't heard of any (until I read the learned replies here). The last comment, by Alex Besogonov, seems to be the best explanation:
Java bytecode is NOT suited to be run on real hardware. It's stack-based, so pipelining goes out of the window. In theory, one can do on-the-fly translation from stack-based to register-based machine, but it'll require A LOT of transistors.
So in reality, it's ALWAYS more effective to JIT-compile Java bytecode and then run it on a common CPU. There is one exception JVMs for low-power devices where the speed of hardware JVM is not a problem (remember Forth CPUs).
Of course, hardware can still provide few features to speed up JVMs. Like hardware-assisted forwarding pointers which allow to create fast real-time compacting pauseless GC (I assume Azul hardware has this support).
This is very interesting. Thank you all for your answers.
回答3:
Azul Systems designs systems from the ground up with (massive services running on) Java in mind, including hardware-assisted garbage collection.
There's also GCJ for compiling Java to native code, though it is not a complete implementation of Java.
回答4:
You might want to try JOP
It's open source and you can try it on your own hardware.
来源：https://stackoverflow.com/questions/4359343/is-there-a-cpu-that-runs-java-in-microcode