RFR: : (coll) IdentityHashMap is resized before exceeding the expected maximum size
ivan.gerasimov at oracle.com
Tue Jul 8 14:01:32 UTC 2014
On 08.07.2014 4:44, Martin Buchholz wrote:
> On Mon, Jul 7, 2014 at 9:41 AM, Martin Buchholz <martinrb at google.com
> <mailto:martinrb at google.com>> wrote:
> I'd like to offer an alternative version of this change. webrev
> coming soon.
> Here's the promised webrev.
> - Fixes a typo in the javadoc.
> - removes the "threshold" field (WAT, a cache to avoid multiplying by 3?)
> - optimizes 3*x into x + x << 1
My personal preference would be x + x + x, but I thought JIT can do this
kind of optimizations itself.
Out of curiosity I've created a microbenchmark:
Benchmark Mode Samples Score Score
o.s.MyBenchmark.testMethod_01_X3 avgt 200 5.900
o.s.MyBenchmark.testMethod_02_PPP avgt 200 6.029
o.s.MyBenchmark.testMethod_03_PSH avgt 200 5.907
On my machine 3*x and x + (x<<1) appear to be of the same speed (#1 and
x + x + x (case #2) happens to be ~2% slower.
Given the optimization doesn't introduce any speedup, wouldn't it be
better to use 3*x for its clarity?
> - adds more test assertions
> - removes the unusual 4/3 slack space for expansion on deserialization.
> TODO: the test should be testng-ified, I think.
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