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https://issues.apache.org/jira/browse/HBASE-14268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14730538#comment-14730538
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Hiroshi Ikeda commented on HBASE-14268:
---------------------------------------
bq. Nice numbers. Out of interest, do you see weak references being collected
in non-full GC?
By the new KeyLocker's outputs in my previously added comment, non-full GC
collects much memory, which is no doubt used for weak references and their
referents.
{quote}
Why do this and not just Iterate the passed in Set?
Object[] keyArray = keys.toArray();
{quote}
The elements are required to sort before locking in order to avoid deadlock.
There are several ways to do this, but I think using array is simpler and
faster than using {{TreeSet}} or {{Collections.sort(List)}}.
{quote}
Why loop twice and not lock as you go: i.e. is this needed:
for (Lock lock : locks.values())
{ 97 lock.lock(); 134 }
98 }
{quote}
That is because the range under the locks should be as small as possible.
> Improve KeyLocker
> -----------------
>
> Key: HBASE-14268
> URL: https://issues.apache.org/jira/browse/HBASE-14268
> Project: HBase
> Issue Type: Improvement
> Components: util
> Reporter: Hiroshi Ikeda
> Assignee: Hiroshi Ikeda
> Priority: Minor
> Fix For: 2.0.0, 1.3.0
>
> Attachments: 14268-V5.patch, HBASE-14268-V2.patch,
> HBASE-14268-V3.patch, HBASE-14268-V4.patch, HBASE-14268-V5.patch,
> HBASE-14268-V5.patch, HBASE-14268-V6.patch, HBASE-14268-V7.patch,
> HBASE-14268-V7.patch, HBASE-14268.patch, KeyLockerPerformance.java
>
>
> 1. In the implementation of {{KeyLocker}} it uses atomic variables inside a
> synchronized block, which doesn't make sense. Moreover, logic inside the
> synchronized block is not trivial so that it makes less performance in heavy
> multi-threaded environment.
> 2. {{KeyLocker}} gives an instance of {{RentrantLock}} which is already
> locked, but it doesn't follow the contract of {{ReentrantLock}} because you
> are not allowed to freely invoke lock/unlock methods under that contract.
> That introduces a potential risk; Whenever you see a variable of the type
> {{RentrantLock}}, you should pay attention to what the included instance is
> coming from.
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