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Your calling method (even there were such method, in fact there is
no such function) will not be executed during STW, since all java
threads stopped. The result is that after JVM resumes all java
threads, your call will return true always. To know the jvm status,
you have to use some agents like JVMTI.<br>
<br>
--Yumin<br>
<br>
On 12/11/2011 7:55 PM, Li Li wrote:
<blockquote
cite="mid:CAFAd71UU4TYBgtM2O7wUro4WNiQ=xAqzgN+QoU3LX-ppf3dGNw@mail.gmail.com"
type="cite"><br>
<div class="gmail_quote">---------- Forwarded message ----------<br>
From: <b class="gmail_sendername">Krystal Mok</b> <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:rednaxelafx@gmail.com">rednaxelafx@gmail.com</a>></span><br>
Date: Sun, Dec 11, 2011 at 5:53 PM<br>
Subject: Re: how to know jvm is stopping the world?<br>
To: Li Li <<a moz-do-not-send="true"
href="mailto:fancyerii@gmail.com">fancyerii@gmail.com</a>><br>
<br>
<br>
HI,
<div><br>
</div>
<div>You're probably looking in the wrong direction. When the
JVM "stops-the-world", it stops the world -- all Java threads
(or "mutators") are suspended. There's no way for you to
execute any Java code during that period.</div>
<div>HotSpot VM uses a "safepoint" mechanism to stop-the-world.
You can get safepoint stats with
-XX:+PrintSafepointStatistics.</div>
<div><br>
</div>
<div>There's an alternative that might help. Try GC notification
with JMX [1]. Setup a notification threshold, and when the
heap usage crosses the threshold, you'll get a notification.
Put the load balancing logic in the callback. Even though this
is different from "a notification of stop-the-world pause", it
might work for you.</div>
<div><br>
</div>
<div>There's a GC notification mechanism in .NET that might have
been closer to what you wanted [2].</div>
<div><br>
</div>
<div>- Kris</div>
<div><br>
</div>
<div>[1]: <a moz-do-not-send="true"
href="http://docs.oracle.com/javase/6/docs/api/java/lang/management/MemoryMXBean.html"
target="_blank">http://docs.oracle.com/javase/6/docs/api/java/lang/management/MemoryMXBean.html</a><br>
[2]: <a moz-do-not-send="true"
href="http://msdn.microsoft.com/en-us/library/cc713687.aspx"
target="_blank">http://msdn.microsoft.com/en-us/library/cc713687.aspx</a></div>
<div>
<div class="h5">
<div><br>
<div class="gmail_quote">On Sun, Dec 11, 2011 at 2:31 PM,
Li Li <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:fancyerii@gmail.com" target="_blank">fancyerii@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt
0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
<div>hi,</div>
<div> In our application of full text searching
with lucene and solr. we will give jvm about 25GB
memory. we use CMS as old generation garbage
collector. But the jvm sometimes can't do anything.
So our clients complain that the connection is time
out. we find the reason is the jvm is doing full gc
and it will stop service for about 1-3 seconds.</div>
<div> I know that this situation is inevitable when
using CMS collector. but we have more than one
searching machines, so if I know jvm is doing full
gc(specially stop the world), I can send requests to
other machines. But the question now is that jvm
don't provide an api for that. I think it's not very
difficult(for guys developing hotspot, but is in
deed difficult for me ). So I want your help.</div>
<div> The first question is where is the position
of CMS full gc.</div>
<div> from <a moz-do-not-send="true"
href="http://blogs.oracle.com/jonthecollector/entry/did_you_know"
target="_blank">http://blogs.oracle.com/jonthecollector/entry/did_you_know</a></div>
<div> there are many steps:</div>
<div> 1. STW initial mark</div>
<div> 2. Concurrent marking</div>
<div> 3. Concurrent precleaning</div>
<div> 4. STW remark</div>
<div> 5. Concurrent sweeping</div>
<div> 6. Concurrent reset</div>
<div> there are 2 stop the world stages. I want to
know the line number(or functions) of this stages.
so I can tell java program that jvm now is doing
full gc.</div>
<div> The second is that how to communicate
between jvm and java program? My expected thing is
like :</div>
<div> //java program</div>
<div> if(System.isStopTheWolrd()){</div>
<div> //system is busy, tell the dispatch
node that don't send request to me</div>
<div> }else{</div>
<div> do service;</div>
<div> }</div>
<div> I have no experience in jvm developing. jvm
is implemented in c and jni is the interface between
them. is there any other method that jvm can achieve
this? obviously, it can extend System class and add
a static method named isStopTheWorld(). Could some
one tell me how to do this in details? Thank you
very much.</div>
</blockquote>
</div>
<br>
</div>
</div>
</div>
</div>
<br>
</blockquote>
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