RFR: 8304743: Compile_lock and SystemDictionary updates [v3]

[Dean Long]

On Sat, 1 Apr 2023 13:27:17 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> The SystemDictionary is updated and read under the Compile_lock but this is unnecessary because the table is a concurrent hashtable, and the lock doesn't really synchronize any other compilation state.  The lock may have protected other state that Dependencies used in the past but has been removed.   See discussion in CR for more information.
>> Tested with tier1-8.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Missing null check

Looks good to me.

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Marked as reviewed by dlong (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13270#pullrequestreview-1369723470