RFR: 8283660: Convert com/sun/jndi/ldap/AbstractLdapNamingEnumeration.java finalizer to Cleaner

[Roger Riggs]

On Wed, 20 Apr 2022 00:32:25 GMT, Brent Christian <bchristi at openjdk.org> wrote:

> Please review this change to replace the finalizer in `AbstractLdapNamingEnumeration` with a Cleaner.
> 
> The pieces of state required for cleanup (`LdapCtx homeCtx`, `LdapResult res`, and `LdapClient enumClnt`) are moved to a static inner class . From there, the change is fairly mechanical.
> 
> Details of note: 
> 1. Some operations need to change the state values (the update() method is probably the most interesting).
> 2. Subclasses need to access `homeCtx`; I added a `homeCtx()` method to read `homeCtx` from the superclass's `state`.
> 
> The test case is based on a copy of `com/sun/jndi/ldap/blits/AddTests/AddNewEntry.java`. A more minimal test case might be possible, but this was done for expediency.
> 
> The test only confirms that the new Cleaner use does not keep the object reachable. It only tests `LdapSearchEnumeration` (not `LdapNamingEnumeration` or `LdapBindingEnumeration`, though all are subclasses of `AbstractLdapNamingEnumeration`). 
> 
> Thanks.

src/java.naming/share/classes/com/sun/jndi/ldap/AbstractLdapNamingEnumeration.java line 132:

> 130:             this.state = new CleaningAction(homeCtx, answer, homeCtx.clnt);
> 131:             // Ensures that context won't get closed from underneath us
> 132:             this.state.homeCtx.incEnumCount();

Readability might be improved by using the new `homeCtx()` method instead of `state.homeCtx` in this file.
It would then be consistent with how subclasses access it.
It depends which style you prefer to be more consistent with.

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PR: https://git.openjdk.java.net/jdk/pull/8311