SoftReference incorrect javadoc?
per.liden at oracle.com
Tue Apr 16 06:27:15 UTC 2019
On 4/16/19 4:19 AM, David Holmes wrote:
> Hi Michael,
> Re-directing to core-libs-dev and hotspot-gc-dev.
> On 16/04/2019 12:14 pm, Michael Pollmeier wrote:
>>> 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.
More information about the core-libs-dev