RFR: 8275811 Incorrect instance to dispose

[Daniel Jeliński]

On Fri, 22 Oct 2021 18:45:31 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

>> The current code that changes cipher suites disposes the new suite instead of the old one, which usually silently fails. This patch fixes the code to dispose the old instance instead.
>> 
>> DTLS appears to be unaffected: DTLSOutputRecord keeps 2 ciphers and correctly [disposes the old one](https://github.com/openjdk/jdk/blob/739769c8fc4b496f08a92225a12d07414537b6c0/src/java.base/share/classes/sun/security/ssl/DTLSOutputRecord.java#L106), and DTLSInputRecord [doesn't dispose anything](https://github.com/openjdk/jdk/blob/4b9303b77b43d890ebacbec38b4ac5db7e171886/src/java.base/share/classes/sun/security/ssl/DTLSInputRecord.java#L57)
>
> Did you want to cover the update for line 222 at OutputRecord.java as well?

After reviewing the scope of changes to fix writeCipher disposal I decided to remove it entirely. It would probably be a nice follow-up enhancement, but I'm not confident I'd implement it correctly on the first try, so I'd rather not introduce it in a bugfix PR. @XueleiFan is that acceptable to you?

On a side note, I had another look at [DTLSOutputRecord](https://github.com/openjdk/jdk/blob/739769c8fc4b496f08a92225a12d07414537b6c0/src/java.base/share/classes/sun/security/ssl/DTLSOutputRecord.java#L106). It looks like we keep a reference to `prevWriteCipher` only to call `dispose()` during the next cipher change. I admit I don't know how often DTLS changes ciphers, but I think GC would have collected that cipher earlier if we didn't keep it.

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PR: https://git.openjdk.java.net/jdk/pull/6084