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From "Geir Magnusson Jr." <g...@pobox.com>
Subject Re: [General VM] GC strategy:how to garbage collect short-lived objects quickly.
Date Thu, 14 Sep 2006 13:34:33 GMT


Jimmy, Jing Lv wrote:
> Leo Li wrote:
>> Hi,all:
>>    As we all know, java objects are allocated on heap instead of stack,
>> thus there is a problem about how to garbage collect short-lived objects
>> quickly.
>>    In a recent real project I involved, a server built on java tries to
>> send thousands of messages to client per second. A lot of short-lived
>> messages is created as objects and discarded. (Although I can recycle 
>> these
>> memory, there is still a byte array created during per call of nio 
>> read and
>> write.) Since current GC strategy adopted by current RI starts to work 
>> only
>> when the memory allocated approaching the limit of java heap, the work 
>> of GC
>> is huge and will raise a wave on the server performance. Furthermore, 
>> after
>> a long run, although I know GC will merge memory, the operating system
>> reports there is memory fragment and in the worst case the OS will even
>> report real memory is exhausted.
>>    Of course it is possible to limit the java heap so as to force gc
>> frequently as a workround, is it preferrable to collect short-lived 
>> objects
>> quickly such as adopt aged-related object queues as one of the gc 
>> strategy?
>>   What about the VMs here, drlvm or J9?
>>
> 
> Interesting topic, I'm still dreaming of "free()" in Java (This dream 
> begins at the very beginning when I see Java, as C/C++ is my first 
> program language )However, it seems RI will never give us "free()". :)

No :)

> 
> Only a thought, Java may offer a key word "temp", indicating that this 
> variety can be freed at once.

How can you tell?  You need to be sure that value of the temp reference 
isn't held by anyone else.  You need to make sure it doesn't escape the 
scope...

geir

> 
>> Leo Li
>> China Software Development Lab, IBM
>>
> 
> 

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