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FWIW: About a year ago, the -O option was a total no-op. Something might have been added since then, but its unlikely. And that information applies to the Sun supplied javac command. I assume platforms could do various things but don't know the intenal logistics of exactly what would be done or how personally. Richard D. Dettinger AS/400 Java Data Access Team Democracy's enemies have always underestimated the courage of the American people. It was true at Concord Bridge. It was true at Pearl Harbor. And it was true today. Rochester Post-Bulletin Tuesday September 11, 2001 Blair Wyman/Rochester/IBM@IBMUS@midrange.com on 01/08/2002 03:11:30 PM Please respond to java400-l@midrange.com Sent by: java400-l-admin@midrange.com To: java400-l@midrange.com cc: Subject: Re: JIT and class loaders David Morris wrote: >Group, > >I searched the iSeries FAQs and can't find a clear description of when >the JVM supports Jar and Class files created using CRTJVAPGM. I am >assuming that if I use a custom class loader (almost any Servlet >container) that the iSeries JVM will have to fall back to the JIT >optimizations if available. Is that true? Also, is inlining possible >with the JIT compiler and does the -O compile option have any affect? Currently, any class loaded via a so-called "user classloader" will be processed (by default) using the JIT. This is an artifact of the way our JVM finds the pre-compiled result of calling CRTJVAPGM, which is using the file's inode. When a user classloader is involved, the JVM never gets to see the actual file (either by name or by inode), and so there's no easy way to get to the JVAPGM. The terminology "fall back" is a little misleading -- the JIT performance is fast approaching the performance of CRTJVAPGM'd code, right on up to level 40. In some cases, even the most aggressive "static" analyses and optimizations, done by CRTJVAPGM at high optimization levels, aren't as effective as the optimizations possible using the JIT's complete knowledge of the runtime environment. (Static optimizations, due to the dynamic nature of Java, have to be "guarded" -- the JIT is under no such restriction.) So, yes, the JIT can and does perform inlining, and in fact can do so when CRTJVAPGM cannot. The -O compile option might have some effect, but that's obviously all happening before either the JIT or CRTJVAPGM get any chance, since it's an option on the javac command. (javac takes source code to bytecode.) I haven't played with it much, but together with javap -c (to disassemble a classfile) it could be interesting to see what it "tries." :) HTH. -blair Blair Wyman -- iSeries JVM -- (507) 253-2891 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ "I was born not knowing, and have had only a little time to change that here and there." -- Richard P. Feynman "David Morris" <David.Morris@plu To: <JAVA400-L@midrange.com> mcreek.com> cc: Sent by: Subject: JIT and class loaders java400-l-admin@m idrange.com 01/08/2002 01:17 PM Please respond to java400-l _______________________________________________ This is the Java Programming on and around the iSeries / AS400 (JAVA400-L) mailing list To post a message email: JAVA400-L@midrange.com To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/cgi-bin/listinfo/java400-l or email: JAVA400-L-request@midrange.com Before posting, please take a moment to review the archives at http://archive.midrange.com/java400-l. _______________________________________________ This is the Java Programming on and around the iSeries / AS400 (JAVA400-L) mailing list To post a message email: JAVA400-L@midrange.com To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/cgi-bin/listinfo/java400-l or email: JAVA400-L-request@midrange.com Before posting, please take a moment to review the archives at http://archive.midrange.com/java400-l.
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