Hi,
As a lurker on this list, I thought I'd share the following article:
http://www.osnews.com/story.php?news_id=10729
This might be a good article for those new to JVMs. It's not as technical
as the various white paper citations being bandied about but it's a nice
introduction to just-in-time-compiling / optimization, Swing threading, and
other JVM performance-related issues.
"I think Java is somehow still seen as an interpreted language; in fact, it
does get compiled to native code using Just In Time (JIT) compilation. It is
also a myth to think that JIT code is slower than pre-compiled code. The
only difference is that bytecode gets JITed once its required (i.e., the
first time a method is called - and the time is negligible) it then gets
cached for subsequent calls. JIT code can benefit from all the same
optimisations that pre-compiled can get, plus some more (from Lewis and
Neumann, 2004):
* The compiler knows what processor it is running on, and can generate code
specifically for that processor. It knows whether (for example) the
processor is a PIII or P4, if SSE2 is present, and how big the caches are. A
pre-compiler on the other hand has to target the least-common-denominator
processor, at least in the case of commercial software.
* Because the compiler knows which classes are actually loaded and being
called, it knows which methods can be de-virtualized and inlined.
(Remarkably, modern Java compilers also know how to "uncompile" inlined
calls in the case where an overriding method is loaded after the JIT
compilation happens.)
* A dynamic compiler may also get the branch prediction hints right more
often than a static compiler."
I assume these will all be goals for a Harmony project JVM?
Best,
WILL
