[jira] Closed: (HARMONY-4869) [classlib][nio][performance] Selector improvements: moving away from O(n) at Java layer, part 1

["Aleksey Shipilev (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HARMONY-4869?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aleksey Shipilev closed HARMONY-4869.
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> [classlib][nio][performance] Selector improvements: moving away from O(n) at Java layer, part 1
> -----------------------------------------------------------------------------------------------
>
>                 Key: HARMONY-4869
>                 URL: https://issues.apache.org/jira/browse/HARMONY-4869
>             Project: Harmony
>          Issue Type: Improvement
>          Components: Classlib
>         Environment: all
>            Reporter: Aleksey Shipilev
>            Assignee: Tim Ellison
>         Attachments: selectors-JL-O1.patch
>
>
> Current implementation of java.nio.channels.Selector is O(n) for Selector.select() operation. 
> There are several causes:
>  1. "keys" is the HashSet, so we spend time on iterating over it
>  2. "keys" are iterated on every select() to prepare the readable and writable arrays for native call
> This patch includes a bunch of optimizations:
>  1. Creates hashCode() and equals() for SelectionKeyImpl to get rid of calling _native_ identityHashCode()
>  2. Changes the internal representation of keys to SelectionKeyImpl[] and adds logic for on-the-fly maintenance
>  3. Adds on-the-fly maintenance for readable and writable arrays, making them prepared right away for every select()
>  4. Adds indexes for easy mapping "keys<->FD"
>  5. Optimizes hotpath in processResults().
> Keeping in mind that count(register) <= count(select), we sure that moving key set maintenance to register() is performance-safe.
> Thus, we simplify one part of Selector.select() call from being O(n) in the Java layer. There are also processResults() scales as O(n) and still portlib and native layers too - they're going to be optimized later too.

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