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Rick Hillegas commented on DERBY-6856:
When I compile Derby using JDK 9 build 167, I see several instances of the following warning:
warning: [deprecation] finalize() in Object has been deprecated
The following deprecation summary now appears in the javadoc for java.lang.Object.finalize():
"Deprecated. The finalization mechanism is inherently problematic. Finalization can lead to performance issues, deadlocks, and hangs. Errors in finalizers can lead to resource leaks; there is no way to cancel finalization if it is no longer necessary; and no ordering is specified among calls to finalize methods of different objects. Furthermore, there are no guarantees regarding the timing of finalization. The finalize method might be called on a finalizable object only after an indefinite delay, if at all. Classes whose instances hold non-heap resources should provide a method to enable explicit release of those resources, and they should also implement AutoCloseable if appropriate. The Cleaner and PhantomReference provide more flexible and efficient ways to release resources when an object becomes unreachable."
Most of these classes do implement AutoCloseable. We should investigate hooking these classes up to the new Cleaner-based mechanism for object rundown. I will need advice from the experts about how to proceed. I would be grateful for any advice from the community about how to use this new Cleaner class.
I am worried that migrating this delicate logic may give rise to heisenbugs which our release processes will not discover. We may want to merely suppress this warning for our first JDK9-built release. We can always migrate to Cleaner-based finalization after the wider Java eco-system has developed best practices around using the Cleaner class.
> Make it possible to build Derby using JDK 9
> Key: DERBY-6856
> URL: https://issues.apache.org/jira/browse/DERBY-6856
> Project: Derby
> Issue Type: Improvement
> Components: Build tools
> Affects Versions: 10.12.1.1
> Reporter: Rick Hillegas
> Attachments: derby-6856-01-ab-addShardingKey.diff, derby-6856-01-ac-cleanup.diff, derby-6856-02-aa-addShardingKey.diff, derby-6856-03-aa-autoboxingDeprecationWarnings.diff, derby-6856-03-ab-autoboxingDeprecationWarnings.diff, derby-6856-04-aa-autoboxingDeprecationWarnings-part2.diff, derby-6856-04-ab-autoboxingDeprecationWarnings-part2.diff, derby-6856-05-ac-roundingMode-Class.newInstance.diff, derby-6856-05-af-roundingMode-Class.getDeclaredConstructor.diff, derby-6856-05-ag-roundingMode-Class.newInstance.diff, derby-6856-06-aa-observable.diff, derby-6856-07-aa-oneMoreNewInstance.diff, derby-6856-08-aa-cleanupJavadoc.diff, derby-6856-09-aa-javadocEntities.diff, derby-6856-10-aa-disable-permissions-subverting-test.diff, derby-6856-11-aa-jigsawResourceLocation.diff, derby-6856-XX-ab-base.diff, derby-6856-XX-ac-base.diff, derby-6856-XX-ad-base.diff, derby-6856-XX-ae-base.diff, PTest.java, ptestScript
> Derby can't be built with JDK 9. Java 9 introduces new JDBC classes like java.sql.ShardingKey and methods which refer to these new classes.
> In addition, project Jigsaw has created a new way to name classes (see http://openjdk.java.net/jeps/220). This breaks the PropertySetter build tool which we use so that old JVMs can compile Derby and so that Derby can be compiled to run on old JVMs.
> It is likely that we will need to leave this issue open throughout the development cycle of Java 9.
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