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From "Yonik Seeley (JIRA)" <>
Subject [jira] Commented: (LUCENE-1607) String.intern() faster alternative
Date Mon, 20 Apr 2009 00:34:47 GMT


Yonik Seeley commented on LUCENE-1607:

The thread safety problem has to do with safe object publication (making an object visible
to a different thread).  Mutable objects generally can't be safely published w/o synchronization....
it has to do with CPU caches in multi-CPU systems.

IIRC, current x86 architectures will see fewer problems since read barriers are no-ops.. caches
are guaranteed to be coherent.  But even on x86, you aren't guaranteed that instructions and
writes won't be reordered...  so the assignment to pool could be visible *before* all the
memory changes that newPool.put() could cause.

> String.intern() faster alternative
> ----------------------------------
>                 Key: LUCENE-1607
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>            Reporter: Earwin Burrfoot
>             Fix For: 2.9
>         Attachments: intern.patch, LUCENE-1607.patch
> By using our own interned string pool on top of default, String.intern() can be greatly
> On my setup (java 6) this alternative runs ~15.8x faster for already interned strings,
and ~2.2x faster for 'new String(interned)'
> For java 5 and 4 speedup is lower, but still considerable.

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