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From: Jonathan Ellis <jbellis@gmail.com>
Date: Sat, 5 Jun 2010 06:10:12 -0700
Message-ID: <AANLkTikN6xSl-eJLbmVMRBAWB_kdJyDS2V7RgTxspnJh@mail.gmail.com>
Subject: Re: PhantomReference in Cassandra
To: dev@cassandra.apache.org
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>From what I have read, allowing the reference to be GC'd itself is
equivalent to calling clear.  Does adding clear() make an observable
difference?

On Sat, Jun 5, 2010 at 1:31 AM, Anty <anty.rao@gmail.com> wrote:
> ---------- Forwarded message ----------
> From: Anty <anty.rao@gmail.com>
> Date: Sat, Jun 5, 2010 at 4:30 PM
> Subject: PhantomReference in Cassandra
> To: user@cassandra.apache.org, chukwa-dev <chukwa-dev@hadoop.apache.org>
>
>
> Hi:All
> in the code of SSTableReader.java
> =A0private static final ReferenceQueue<SSTableReader> finalizerQueue =3D =
new
> ReferenceQueue<SSTableReader>()
> =A0 =A0{{
> =A0 =A0 =A0 =A0Runnable runnable =3D new Runnable()
> =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0public void run()
> =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0while (true)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0SSTableDeletingReference r =3D nul=
l;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0try
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0r =3D (SSTableDeletingRefe=
rence)
> finalizerQueue.remove();
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0finalizers.remove(r);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0catch (InterruptedException e)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0throw new RuntimeException=
(e);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0try
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0r.cleanup();
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0catch (IOException e)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0logger.error("Error deleti=
ng " + r.path, e);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0};
> =A0 =A0 =A0 =A0new Thread(runnable, "SSTABLE-DELETER").start();
> =A0 =A0}};
>
>
> the PhantomReference SSTableDeletingReference's cleanup() method doesn't
> invoked clear() method inherited from Reference, whichi clear the phantom
> reference to the referent.
> but,the GC enqueues the PhantomReference onto ReferenceQueue before the
> phantom reference clears. Is it necessary to invoke the clear() method af=
ter
> r.clearup() or add clear() method in cleanup() method to accelerate the G=
C
> process.
> =A0 =A0try
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0r.cleanup();
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0r.clear();
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0catch (IOException e)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0{
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0logger.error("Error deleti=
ng " + r.path, e);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> --
> Best Regards
> Anty Rao
>
>
>
> --
> Best Regards
> Anty Rao
>



--=20
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com