JDK-8263467: Incorrect double-checked locking in sun.java2d.CRenderer

[shipilev]

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?

---

Progress

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Issue

• JDK-8263467: Incorrect double-checked locking in sun.java2d.CRenderer

Reviewers

• Phil Race (@prrace - Reviewer)
• Alexander Zvegintsev (@azvegint - Reviewer)

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[mlbridge]

Webrevs

• 01: Full - Incremental (d912f55)
• 00: Full (c81b9ea)

[mrserb]

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).

[shipilev]

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?

[mrserb]

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?

I guess that synchronization became redundant because the field was moved to the local var. But before that, it guarded the method in question for multithreaded access and that was not part of the DCL. So it will be better to return those fields back.

As the test I have run all automated tests and some manual tests, none of them triggered this code.

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[shipilev]

Not now, bot.

[prrace]

LGTM

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8263467: Incorrect double-checked locking in sun.java2d.CRenderer

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At the time when this comment was updated there had been 929 new commits pushed to the master branch:

• 3af4efd: 8265291: Error in Javadoc for doAccessibleAction API in AccessibleJSlider class
• be4f25b: 8266369: (se) Add wepoll based Selector
• ff77ca8: 8266675: Optimize IntHashTable for encapsulation and ease of use
• 04fad70: 8266765: [BACKOUT] JDK-8255493 Support for pre-generated java.lang.invoke classes in CDS dynamic archive
• 0790e60: 8196743: jstatd doesn't see new Java processes inside Docker container
• c6aa8f1: 8232644: bugs in serialized-form.html
• b5b3119: 8266589: (fs) Improve performance of Files.copy() on macOS using copyfile(3)
• 947d69d: 8265042: javadoc HTML files not generated for types nested in records
• 946b0fe: 8266645: javac should not check for sealed supertypes in intersection types
• 74fecc0: 8266503: [UL] Make Decorations safely copy-able and reduce their size
• ... and 919 more: https://git.openjdk.java.net/jdk/compare/7ed46bd02e66415f3a9ce03b93e4469f9277aff5...master

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[mrserb]

I guess that synchronization became redundant because the field was moved to the local var. But before that, it guarded the method in question for multithreaded access and that was not part of the DCL. So it will be better to return those fields back.

Is not approved yet, see above.

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[turbanoff]

Seems this PR was lost for some reason.
@shipilev can you please reopen it? Issue is still actual.