what functions are included in a JVM

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+2 Q:

what functions are included in a JVM

What are the functions of the JVM? All I know are:

JIT compiler
GC
memory allocator

What are the steps it does when you load a Java application?

I am wondering because if I compare the loading time of a Java application with these steps:

InitializeNativeTarget on LLVM
some GC initialization
some Qt/GTK/whatever init
some JIT/ahead compilation of parts of the app
the app init itself

It seems to me that the JVM takes much longer to load than it would take to do the steps I listed above. So what does it do in addition to that?

+1 A:

That's actually a very interesting question - to see for yourself, run a Hello World program giving the option -XX:-TraceClassLoading to the java executable.

Tassos Bassoukos 2010-08-17 01:58:05

Also turn on GC logging.

Stephen C 2010-08-17 01:58:50

I tried `java -verbose:gc -XX:-TraceClassLoading JavaHelloWorld` but all it outputs is just `Hello World`. Do I miss something?

Albert 2010-08-17 02:35:36

@Albert: `-XX:+TraceClassLoading`

Stephen C 2010-08-17 02:53:26

Hm, that seems to just show me what classes are loaded by the JVM (which is *a lot*). But what is the JVM itself doing before that? And what could be stripped out of that? Because it seems to me that it does not need almost any of the stuff which shows up there.

Albert 2010-09-27 21:17:11

It bootstraps the whole JVM from scratch. That takes a while.

Thorbjørn Ravn Andersen 2010-08-17 06:42:22

How exactly does the bootstrap looks like?

Albert 2010-09-27 21:17:33

Use the "-verbose" flag to see each class as it is pulled in by a class loader. You might be surprised...

Thorbjørn Ravn Andersen 2010-09-27 21:30:35

ansaurus

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what functions are included in a JVM

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