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From "Andrey Gura (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IGNITE-6736) Java 9: rework GridCacheMapEntry synchronization logic to avoid Unsafe.monitor* methods
Date Fri, 12 Jan 2018 11:52:02 GMT

    [ https://issues.apache.org/jira/browse/IGNITE-6736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16323860#comment-16323860
] 

Andrey Gura commented on IGNITE-6736:
-------------------------------------

LGTM. Perfromance tests are ok. But now we have additional memory overhead on each entry.

Merged to master branch.

> Java 9: rework GridCacheMapEntry synchronization logic to avoid Unsafe.monitor* methods
> ---------------------------------------------------------------------------------------
>
>                 Key: IGNITE-6736
>                 URL: https://issues.apache.org/jira/browse/IGNITE-6736
>             Project: Ignite
>          Issue Type: Task
>          Components: cache
>            Reporter: Vladimir Ozerov
>            Assignee: Andrey Kuznetsov
>             Fix For: 2.4
>
>
> {{GridCacheMapEntry}} class rely on {{synchronized}} on itself heavily. In {{ATOMIC}}
caches we lock multiple entries at once using {{Unsafe.monitorEnter/Exit}} methods. Unfortunately
these methods were removed in Java 9. Recursion is not an option, as it would cause stack
overflow for {{putAll}} operations with multiple entries.
> Possible fixes:
> 1) Rework {{synchronized}} to {{ReentrantLock}}. Easy, but may cause additional memory
pressure.
> 2) Have different implementations for Java 8 ({{synchronzied}}) and Java 9 ({{ReentrantLock}})
- much more complex solution, because we will require separate module for Java 8 and Java
9.
> 3) Rework {{ATOMIC}} caches, so that {{putAll}} operation updates entries one-by-one.
As a side effect it will eliminate deadlocks.



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