RFR: 8209120: Archive the Integer.IntegerCache (original) (raw)

Claes Redestad claes.redestad at oracle.com
Thu Aug 9 16:17:52 UTC 2018

Hi Peter,

On 2018-08-09 17:32, Peter Levart wrote:

Hi Claes,

When is this archived cache created?

The cache you build when dumping the archive is serialized, so java -Xshare:dump -XX:AutoBoxCacheMax=20000 would create an array with 20k elements in the archive...

Is it possible to create archived cache with java.lang.Integer.IntegerCache.high system property set to > 127 ?

Yes. I'm going to add a test that all variants work though, as Alan suggested.

Wouldn't then at runtime, when cache is initialized from such oversized archive and no java.lang.Integer.IntegerCache.high system property is specified, the resulting cache array be to big?

Perhaps you could allocate a copy of the prefix of the de-archived array in that case to release the unused Integer instances.

The array would be too big, true, but it's backed by the read-only data in the archive directly, so while the Objects might appear in a heap dump, creating them happens at no extra cost and keeping them shouldn't actually cause any real (rss) memory footprint (GC shouldn't be scanning the memory, either).

As accesses to the array is guarded by checking IntegerCache.high (and not cache.length) we won't return cached Integers outside of the requested range, either.

So unless I'm mistaken, defensively allocating a copy shouldn't be necessary.

/Claes

Regards, Peter On 08/09/2018 01:33 PM, Claes Redestad wrote: Hi,

using the new ability to archive immutable heap graphs into the CDS archive, even archiving small things like the Integer.IntegerCache can be profitable. Webrev: http://cr.openjdk.java.net/~redestad/8209120/open.00/ Bug: https://bugs.openjdk.java.net/browse/JDK-8209120 For a default cache (256 elements), this change saves us ~1 million instructions. Applications that use -XX:AutoBoxCacheMax can profit further (and we can use this to stress test the archiving feature..) The patch is built on top of and tested with Jiangli's patch for https://bugs.openjdk.java.net/browse/JDK-8207263 and I don't intent to push this before that is in. Thanks! /Claes

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