SoftReferences Survival in JRockit R26

Question

Hi Pankaj,
This behaviour has changed to JRockit codeline R26, you could observe how the references are cleared with –Xverbose:references.
According to the JVM specification, (only) softly reachable objects are guaranteed to be cleared before the JVM throws OOME, nothing else is specified and it’s up to the JVM to handle this in the best way. If the objects are held by both a SoftReference and another (hard) reference, the object will remain in the heap at least until the hard reference has vanished.
In the R26 line, soft references are cleared depending on the amount of free java heap memory after a garbage collection. By default, a softly reachable object will survive at least 0.5s*MB of free memory since it was last touched.
Example: If the garbage collector leaves 100MB of free memory, a softly reachable object will survive at least 0.5 * 100s = 50s, after the last time it was touched.
This survive timer could be tuned with the flag –XXsoftrefMSSurvivalRate:<value>, state the new value in ms (default 500).
Kind regards, Cecilia
JRockit Customer Centric Engineering
<i>From: Pankaj Sawhney
Sent: den 20 juni 2006 23:24
Subject: JRockit handling of Soft References?
Hi
IHAC who wants to know does JRockit employs some kind of algorithm (like LRU) to handle soft references while removing them from memory during the GC. I did some research and came across on dev2dev forum that the soft references are removed to avoid OOM conditions. Also the object is removed after couple of GC cycles, if it is not used. Is this predictable or configurable (number of GC cycles the object can survive if not used?)
http://forums.bea.com/bea/message.jspa?messageID=200010534&tstart=0
The discussion on this topic in the above link seems long back. Any pointers which suggest that we have some new feature or altered behavior in new JRockit releases for handling of soft references will be appreciated.
Thanks
Pankaj
</i>
Kind regards,
Cecilia Borg
BEA WebLogic JRockit

Answer 1

Hi Pankaj,
This behaviour has changed to JRockit codeline R26, you could observe how the references are cleared with –Xverbose:references.
According to the JVM specification, (only) softly reachable objects are guaranteed to be cleared before the JVM throws OOME, nothing else is specified and it’s up to the JVM to handle this in the best way. If the objects are held by both a SoftReference and another (hard) reference, the object will remain in the heap at least until the hard reference has vanished.
In the R26 line, soft references are cleared depending on the amount of free java heap memory after a garbage collection. By default, a softly reachable object will survive at least 0.5s*MB of free memory since it was last touched.
Example: If the garbage collector leaves 100MB of free memory, a softly reachable object will survive at least 0.5 * 100s = 50s, after the last time it was touched.
This survive timer could be tuned with the flag –XXsoftrefMSSurvivalRate:<value>, state the new value in ms (default 500).
Kind regards, Cecilia
JRockit Customer Centric Engineering
<i>From: Pankaj Sawhney
Sent: den 20 juni 2006 23:24
Subject: JRockit handling of Soft References?
Hi
IHAC who wants to know does JRockit employs some kind of algorithm (like LRU) to handle soft references while removing them from memory during the GC. I did some research and came across on dev2dev forum that the soft references are removed to avoid OOM conditions. Also the object is removed after couple of GC cycles, if it is not used. Is this predictable or configurable (number of GC cycles the object can survive if not used?)
http://forums.bea.com/bea/message.jspa?messageID=200010534&tstart=0
The discussion on this topic in the above link seems long back. Any pointers which suggest that we have some new feature or altered behavior in new JRockit releases for handling of soft references will be appreciated.
Thanks
Pankaj
</i>
Kind regards,
Cecilia Borg
BEA WebLogic JRockit