RFR: 8284855: Update needed to Cleaners added to jdk.crypto.cryptoki

[Daniel Fuchs]

On Thu, 14 Apr 2022 18:06:10 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

> This is an effort to fix a problem introduced in the fix for [JDK-8284368](https://bugs.openjdk.java.net/browse/JDK-8284368), which replaced the finalizers in jdk.crypto.cryptoki with Cleaners.  However, there is a problem with the code changes. The Runnables registered with Cleaner refer to the object being registered ('this'). Meaning, the Cleaner mechanism will keep the objects reachable, preventing them from being cleaned and collected.

src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/wrapper/PKCS11.java line 168:

> 166:         // Calls disconnect() to cleanup the native part of the wrapper.
> 167:         Cleaner.create().register(this,
> 168:             () -> PKCS11.disconnect(pNativeData));

If I'm not mistaken each new call to Cleaner.create() will create a new cleaner and a new deamon thread for it, so it's not recommended to create one cleaner per object.
Also it might be worth double checking that the lambda created here doesn't capture `this`: IIRC there were some subtle cases where a lambda could unexpectedly capture `this`.

Also probably the cleaner itself can't be GC'ed while its thread is running but you might be relying on undocumented behavior. It would be more prudent to stick it in a static variable to retain a strong reference.

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PR: https://git.openjdk.java.net/jdk/pull/8248