RFR: 8145680: Remove unnecessary explicit initialization of volatile variables in java.base

[Jason Mehrens]

Claes,

For the cases where boolean was being assigned to 'true' (ASSCI and FileLockImpl) does it hurt performance since the accessor methods will now include a branch at the bytecode level?  See: "Speed-kings of inverting booleans" at  http://www.javaspecialists.eu/archive/Issue042.html

Jason
________________________________________
From: core-libs-dev <core-libs-dev-bounces at openjdk.java.net> on behalf of Claes Redestad <claes.redestad at oracle.com>
Sent: Sunday, December 20, 2015 11:29 AM
To: core-libs-dev at openjdk.java.net
Subject: Re: RFR: 8145680: Remove unnecessary explicit initialization of        volatile variables in java.base

Hi,

the changes to java.net.URI stood out as a bit too intrusive for a
cleanup like this, and there's precious little measurable benefit. I
decided to break out those to a separate RFE and simplified this patch:

Webrev: http://cr.openjdk.java.net/~redestad/8145680/webrev.02

/Claes

On 2015-12-19 14:07, Claes Redestad wrote:
> Hi,
>
> initializing volatile fields to their default value has a well-known
> performance penalty, and removing these should typically be safe. This
> patch addresses java.base.
>
> There are however some corner cases that we need to check for, see
> examples and discussion in
> http://cs.oswego.edu/pipermail/concurrency-interest/2015-December/014767.html
>
> When meticulously going through and checking each usage for odd
> pattern like this I accidentally did a bit of extra cleanup, mostly
> addressing a number of cases where the volatile field was being read
> twice. Sorry!
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8145680
>