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From "Wenlong Li" <wenl...@gmail.com>
Subject Re: [performance] Startup cost is high for Harmony (HARMONY-6002)
Date Thu, 13 Nov 2008 07:40:36 GMT

Hello, all,
I collect the required classes/packages/jars in
http://issues.apache.org/jira/browse/HARMONY-6002. As we discussed, we
can package these classes into the bootstramp.jar, and handle other
classes/jars on demand.

In my mind, we can parse all jars at startup, and only save the
manifest of each jar (except bootstramp.jar with all jars loaded
during startup). Later, when a new class is required, we can parse the
manifest to see this class in which jar, and then read all classes in
this jar to class cache (because I/O is also expensive, so I think we
should read all classes in this jar). As for implementation, I think
we can add code in LoadFromJarFile of classloader.cpp to support
on-demand jar/class parsing and loading. Is my understanding correct?
One more question is how to generate bootstramp.jar automatically? At
this moment, we can manually produce it, but it doesn't make sense for
a product. I guess we need make some modification on the modularity
under working_classlib\modules

What do you think?


On Wed, Nov 12, 2008 at 11:48 PM, Tim Ellison <t.p.ellison@gmail.com> wrote:
> Wenlong Li wrote:
>> Yes, I also noticed the manifest in each jar has keyword, like
>> export-package to define  which packages are provided by this jar. I
>> think that would be one heuristics for us to decide parsing this jar
>> or not. I will try to add the on-demand jar parsing feature into
>> Harmony by using this rule information.
> Good idea.  Or introduce the concept of a start-up classpath ... so you
> don't have to hard-code in the VM which packages are in the start-up
> sequence.
> Right now there is the bootclasspath and application classpath.  We
> expect all the start-up classes plus more to be on the bootclasspath.
> But if we split that into the bootclasspath={start-up path + system
> path} classes then we can preload / process the JARs on the start-up
> classpath, and defer the parsing of those on the system classpath.  Just
> as a start-up differentiator, the start-up+system JARs would of course
> all be part of the bootclasspath to the application.
> Just an idea...
> Regards,
> Tim

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