how to know jvm is stopping the world?

[Krystal Mok]

The GC start/end events in JVMTI are available since a long time ago. You
can use it in JDK 6 right now. [1] And in OpenJDK 7, too.

The problem (for you) is this interface does not allow you to execute any
Java code in the event callback. You'll need make some non-Java interface
in your dispatcher so that this notification can ultimately propagate from
the JVM in full GC to your dispatcher.

- Kris

[1]:
http://docs.oracle.com/javase/6/docs/platform/jvmti/jvmti.html#GarbageCollectionStart

On Tue, Dec 13, 2011 at 11:40 AM, Li Li <fancyerii at gmail.com> wrote:

> That's what I want.
> btw, this feature is only available in sun jdk7?
> does it exist in openjdk7?
>
>
> On Mon, Dec 12, 2011 at 11:06 PM, Stefan Karlsson <
> stefan.karlsson at oracle.com> wrote:
>
>> On 12/11/2011 07:31 AM, Li Li wrote:
>>
>>> hi,
>>>    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.
>>>    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.
>>>    The first question is where is the position of CMS full gc.
>>>    from http://blogs.oracle.com/**jonthecollector/entry/did_you_**know<http://blogs.oracle.com/jonthecollector/entry/did_you_know>
>>>    there are many steps:
>>>      1. STW initial mark
>>>      2. Concurrent marking
>>>      3. Concurrent precleaning
>>>      4. STW remark
>>>      5. Concurrent sweeping
>>>      6. Concurrent reset
>>>    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.
>>>     The second is that how to communicate between jvm and java program?
>>> My expected thing is like :
>>>     //java program
>>>     if(System.isStopTheWolrd()){
>>>           //system is busy, tell the dispatch node that don't send
>>> request to me
>>>     }else{
>>>           do service;
>>>     }
>>>     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.
>>>
>>
>> You could probably use JVMTI. See: http://docs.oracle.com/javase/**
>> 7/docs/platform/jvmti/jvmti.**html#GarbageCollectionStart<http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#GarbageCollectionStart>
>>
>> StefanK
>>
>
>
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