PhantomReference: why not cleared by GC when enqueued? (original) (raw)

Kirk Pepperdine kirk at kodewerk.com
Thu May 30 13:21:47 UTC 2013

The only useful use case that I've come up with for PhantomReference is to subclass it. In one case it was used as a wrapper so that we'd know when an object was being collected so that we could reap life-cycle information from it. The behaviour was triggered by an JMX control. I suppose there were other ways to do this but given I only wanted to collect when the object was about to be GC'ed.....

Regards, Kirk

On 2013-05-30, at 1:32 PM, Dmytro Sheyko <dmytro_sheyko at hotmail.com> wrote:

Mark,

You are listed as an author of java.lang.ref classes. So you must know more than others. Could you shed light on this? Thank you, Dmytro From: dmytrosheyko at hotmail.com To: hotspot-gc-dev at openjdk.java.net; core-libs-dev at openjdk.java.net Subject: PhantomReference: why not cleared by GC when enqueued? Date: Wed, 29 May 2013 14:45:54 +0300 Hello, Why phantom references are not automatically cleared by the garbage collector as they are enqueued? Keeping phantom reachable objects in heap has some drawbacks: 1. At least 2 GC are required in order to reclaim them, even in case when application code pulls references from reference queue and clears them promptly. 2. GC pauses are increased since phantom reachable objects are still to be marked. On the other hand, benefits are not obvious. How we can use referent if it's not accessible? Regards, Dmytro

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