Hi Michael,
On 4/16/19 4:19 AM, David Holmes wrote:
Hi Michael,
Re-directing to core-libs-dev and hotspot-gc-dev.
Thanks,
David
On 16/04/2019 12:14 pm, Michael Pollmeier wrote:
Quoting
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/ref/SoftReference.html
All soft references to softly-reachable objects are guaranteed to have
been cleared before the virtual machine throws an OutOfMemoryError
That statement was true when soft references were first introduced in
java 1.2, but from java 1.3.1 the jvm property
`-XX:SoftRefLRUPolicyMSPerMB` was introduced.
That statement is still true. When the GC gets into a situation where it
is having trouble satisfying an allocation, then SoftRefLRUPolicyMSPerMB
will be ignored and all soft references will be cleared, before the GC
gives up and throws an OOME.
It defaults to 1000 (milliseconds), meaning that if there’s only 10MB
available heap, the garbage collector will free references that have
been used more than 10s ago. I.e. everything else (including young
softly reachable objects) will *not* be freed, leading to an
OutOfMemoryError, contradicting the above quoted 'guarantee'.
That's also the behaviour I observed on various JREs. Would you agree,
i.e. should I propose an updated doc?
Could you elaborate on what kind of test you did to come to this
conclusion? Preferably provide a re-producer. In OOME situations, if a
SoftReference isn't cleared, it is typically because you have
unknowingly made it strongly reachable.
cheers,
Per
