On Fri, 12 Mar 2021 03:19:12 GMT, Sergey Bylokhov <s...@openjdk.org> wrote:
>> SonarCloud reports multiple incorrect double-checked locking cases in
>> `sun.java2d.CRenderer`. For example:
>>
>> Arc2D arcToShape;
>>
>> ...
>> if (arcToShape == null) {
>> synchronized (this) {
>> if (arcToShape == null) {
>> arcToShape = new Arc2D.Float();
>> }
>> }
>> }
>>
>> `Arc2D` contains fields that are not `final`. `arcToShape` is not
>> `volatile`. This makes it an incorrect DCL.
>> This code is used by Mac OS, do it would probably blow up some time later on
>> M1.
>>
>> This is the candidate fix that preserves the semantics. I am doing this fix
>> blindly so far, without testing on real Mac OS. But maybe there is no need
>> to do any of this, because the setter methods overwrite the contents of all
>> these objects under their own sync. So, maybe we can just allocate those
>> objects without DCL-backed caching and pass them in?
>
> I guess "Incorrect double-checked" is a too strict description of this code,
> it just tried to eliminate the creation of one object and do not care about
> the content of that object, since it is immediately overridden.
>
> I think It will be more clear to just eliminate this DCL since overhead and
> code complexity seems too much to just cache five objects.
>
> Probably it was important in past(jdk6 and below) when this renderer was used
> for onscreen rendering. Currently, it is used for printing(if actually used
> at all).
Ok, I removed the "DCL" from that code and used the objects directly. AFAICS,
synchronization is redundant on those local objects. What would be a good test
for this change?
-------------
PR: https://git.openjdk.java.net/jdk/pull/2948
