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Date: Wed, 24 Aug 2011 15:12:27 -0700
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 <CADcMMgHAjGtvaf+xvJuDXuhDCMPk_7UA0MAXsUzC3tX4hqVx6w@mail.gmail.com>
Subject: Re: Why doesn't HConnectionManager implement double checked locking ?
From: Stack <stack@duboce.net>
To: dev@hbase.apache.org
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How would double-checked -- a problematic pattern at the best of times
in java (see http://en.wikipedia.org/wiki/Double-checked_locking) --
help here?  What you thinking?  We can't really do putIfAbsent w/ a
connection instance?

Good on you Akash,
St.Ack

On Tue, Aug 23, 2011 at 11:45 AM, Akash Ashok <thehellmaker@gmail.com> wrot=
e:
> Hi,
> =A0 =A0 I have pasted the code below for HConnectionManager.getConnection
>
> =A0public static HConnection getConnection(Configuration conf)
> =A0throws ZooKeeperConnectionException {
> =A0 =A0HConnectionKey connectionKey =3D new HConnectionKey(conf);
> =A0 =A0synchronized (HBASE_INSTANCES) {
> =A0 =A0 =A0HConnectionImplementation connection =3D
> HBASE_INSTANCES.get(connectionKey);
> =A0 =A0 =A0if (connection =3D=3D null) {
> =A0 =A0 =A0 =A0connection =3D new HConnectionImplementation(conf);
> =A0 =A0 =A0 =A0HBASE_INSTANCES.put(connectionKey, connection);
> =A0 =A0 =A0}
> =A0 =A0 =A0connection.incCount();
> =A0 =A0 =A0return connection;
> =A0 =A0}
> =A0}
>
> just curious as to why double checked locking isn't implemented here ? Is=
 it
> because there's won't be too many threads calling this method simultaneou=
ly.
> ?
>
> Cheers,
> Akash A
>