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Date: Fri, 01 Jun 2007 10:53:56 +0200
From: Sebastiaan van Erk <sebster@sebster.com>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: NIOSelector busy wait
References: <463A16EA.5070309@sebster.com> <463A1F1F.5060900@hanik.com>
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Hi,

Filip Hanik - Dev Lists wrote:
> it will return 0 after the timeout has expired if there was no events.
> most likely its not a bug in the JDK but in your linux kernel/distro
>
I just found the Sun bug report + workaround confirming this issue as a 
Linux JDK bug.

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6403933

It's fixed in Java 7, earlier versions are not reported to be fixed, so 
I'm guessing they're not backporting the fix, though I hope they do, 
since it's a serious problem.

> so far I haven't seen the behavior you've explained.
>
In my Comet application I'm seeing this problem consistently: the Tomcat 
poller thread goes into a busy loop with the selector returning 0. Could 
be I'm forgetting to do something which causes this, but I haven't found 
a way to solve the problem yet.

Regards,
Sebastiaan

> Filip
>
> Sebastiaan van Erk wrote:
>> Hi,
>>
>> I have a problem that sometimes the NIO selector goes into a busy 
>> wait loop.
>>
>> In line 1430 the code of NIOEndpoint.java,
>>
>>                            keyCount = selector.select(selectorTimeout);
>>
>> select keeps returning 0 without waiting.
>>
>> I'm running on the latest trunk version of tomcat 6, on Ubuntu Linux 
>> Feisty, with java version:
>>
>> java version "1.6.0"
>> Java(TM) SE Runtime Environment (build 1.6.0-b105)
>> Java HotSpot(TM) Server VM (build 1.6.0-b105, mixed mode)
>>
>> However, I've seen this same behavior with other JDK's (1.5).
>>
>> To me it seems that it's a bug in the JVM implementation because 
>> select should only return 0 if it's woken up, which does not happen 
>> (since all other threads are suspended in my debugger). However, I 
>> was wondering if anybody else has seen this behavior and perhaps 
>> knows what's causing it in the first place.
>>
>> Regards,
>> Sebastiaan
>>
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