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https://issues.apache.org/jira/browse/DIRMINA-751?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Emmanuel Lecharny resolved DIRMINA-751.
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Resolution: Fixed
Ok, I will apply the test, but the code will keep the 3 lines long method just
because I'm not sure our users want to waste almost one Mb of memory to speed
up a method which can be executed one billion time per second on my computer :)
(the lookup table method can be executed 4 billions times !)
What I mean is that it's fun, but it's less maintainable, it eats a lot of
memory, and the improvement will be unoticable. I would rather keep the easier
(3 lines of code method) and with a smaller memory footprint method.
The initial code was suboptimal, and it was good that you guys pointed that !
Keep going, I'm sure that there are a lot of place in MINA that can be
improved, I really appreciate what you both have done !
> IoBuffer.normalizeCapacity improvement
> --------------------------------------
>
> Key: DIRMINA-751
> URL: https://issues.apache.org/jira/browse/DIRMINA-751
> Project: MINA
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0.0-RC1
> Environment: N/A
> Reporter: Bogdan Pistol
> Priority: Minor
> Fix For: 2.0.0-RC2
>
> Attachments: IoBufferTest.java, IoBufferTest.java, IoBufferTest.java,
> patch-lookup-tables.txt, patch.txt
>
>
> The technique of computing the minimum power of 2 that is bigger than the
> requestedCapacity in the
> org.apache.mina.core.buffer.IoBuffer.normalizeCapacity() is not optimal.
> The current computation is as follows:
> int newCapacity = 1;
> while ( newCapacity < requestedCapacity ) {
> newCapacity <<= 1;
> if ( newCapacity < 0 ) {
> return Integer.MAX_VALUE;
> }
> }
> The time complexity of this is O(n), where n is the number of bits of the
> requestedCapacity integer, that is log2(requestedCapacity) - maximum 31.
> This creates an unnecessary overhead in some high IoBuffer allocations
> scenarios that are calling IoBuffer.normalizeCapacity() a lot when creating
> IoBuffers. I observed this when benchmarking a MINA server with hprof.
> There is a better solution to this problem than to iterate the bits from 0 to
> log2(requestedCapacity).
> The alternative is to use a binary search technique that has optimal time
> complexity of O(5). Because requestedCapacity is an integer and has a maximum
> of 2^5 (32) bits we can binary search in the set of bits and determine in
> O(5) comparisons the minimum power of 2 that is bigger than the
> requestedCapacity.
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