RFR: 8334495: Use FFM instead of jdk.internal.misc.Unsafe in java.desktop font implementation [v4]

[Jayathirth D V]

On Wed, 17 Jul 2024 21:30:36 GMT, Phil Race <prr at openjdk.org> wrote:

>> Migrate font code from jdk.internal.misc.Unsafe to using FFM.
>> This reduces the coupling between the java.desktop module and the internals of the java.base module.
>> 
>> The code being changed here is not particularly performance sensitive, and it is not executed in the most common cases.
>> The main impact performance-wise is a total of around 37ms in initialisation costs on my x64 macbook.
>> A minimal program that just draws a string to an image - does not even put up a window - runs at around 690-700ms.
>> There's variability in that number and the overall time for a JDK without the change is around (660-670ms)
>> In the small test, this is the first and only use of FFM, so the one-off part cost should move elsewhere when FFM starts
>> to be used earlier in the JDK itself.
>
> Phil Race has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8334495

Change looks good to me.
Its good that we have captured the time for computation when we have FFM usage at more than one place and how FFM initialization overhead is hit only once.

Also in https://github.com/openjdk/jdk/pull/15476 we had FFM initialization cost of 75ms and now we are seeing 55ms number. If same hardware & software conditions were present between https://github.com/openjdk/jdk/pull/15476 and this PR, may be we are moving towards lower FFM initialization cost.

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Marked as reviewed by jdv (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19777#pullrequestreview-2186402640