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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16642) Use DelayQueue instead of TimeoutBlockingQueue
Date Mon, 03 Oct 2016 09:14:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15541942#comment-15541942

Hiroshi Ikeda commented on HBASE-16642:

Oops, I didn't realize that a single thread execute the timeout task...DelayQueue is more
sophisticated than TimeoutBlockingQueue by preventing needless context switch to wake up waiting
threads, but that advantage will not be shown in this case.

Overhead of creating an object is about equal to overhead of a synchronization without contention.
If you worry about creating objects, you should rather count accessing volatile fields or
Atomic*, but many classes for mutli-threads already use them in order to avoid context switches,
which have about 100-fold overhead. Moreover, creating objects can be optimized by Java in
runtime, and might be removed or be placed in stack instead of heap by escape analysis.

ProcedureExecutor makes TimeBlockingQueue call the current time twice per one comparison,
and that is enough for motivation to do something. Apparent cleanness is not always justified;
Lack of codes makes TimeoutBlockingQueue's behavior vague and confusing, and actually ProcedureExecutor
fails and has risk of busy loop when interrupted. Some methods in TimeoutBlockignQueue breaks
thread-safety with lack of sufficient synchronization. 

Creating the independent class is too early abstraction and rather loses flexibility in future
with paying cost. The using poisons with some behaviors is specific and enough just for ProcedureExecutor.

In second thought, instead of poison it seems preferable to use ScheduledThreadPoolExecutor,
which supports shutdown and some shutdown policies.

> Use DelayQueue instead of TimeoutBlockingQueue
> ----------------------------------------------
>                 Key: HBASE-16642
>                 URL: https://issues.apache.org/jira/browse/HBASE-16642
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Hiroshi Ikeda
>            Priority: Minor
>         Attachments: HBASE-16642.master.V1.patch
> Enqueue poisons in order to wake up and end the internal threads.

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