RFR: 8149330: Capacity of StringBuilder should not get close to Integer.MAX_VALUE unless necessary

Ivan Gerasimov ivan.gerasimov at oracle.com
Mon Feb 22 23:36:59 UTC 2016

On 22.02.2016 22:49, Martin Buchholz wrote:
> Can you make the code look more like the recently optimized code in
> ArrayList and Vector?

Sure.  Please find the updated webrev below.
Of course, there are nuances, as we need to deal with the compact 
strings, so the code isn't quite the same as in ArrayList.


Sincerely yours,

> On Mon, Feb 22, 2016 at 11:20 AM, Ivan Gerasimov
> <ivan.gerasimov at oracle.com> wrote:
>> Hello!
>> When the capacity of a StringBuilder needs to be increased (either due to
>> append() or due to explicit call to ensureCapacity()), the new capacity is
>> calculated as "twice the old capacity, plus 2", rounded down to
>> Integer.MAX_VALUE:
>> http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html#ensureCapacity-int-
>> Because of that, StringBuilder throws OOM early, even though there may be
>> room to grow.
>> The proposed solution is to reserve a few bytes at the top of the range and
>> only try to allocate them if absolutely required.
>> The regression test is @ignored by default, as it is too greedy for memory.
>> Would you please help review the fix?
>> BUGURL: https://bugs.openjdk.java.net/browse/JDK-8149330
>> WEBREV: http://cr.openjdk.java.net/~igerasim/8149330/00/webrev/
>> Sincerely yours,
>> Ivan

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