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

[Phil Race]

On Mon, 24 Jun 2024 18:07:11 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> src/java.desktop/share/classes/sun/font/StrikeCache.java line 151:
>> 
>>> 149: 
>>> 150:     @SuppressWarnings("restricted")
>>> 151:     static final float getGlyphXAdvance(long ptr) {
>> 
>> now, I'm not an expert of this code, but I notice that you have accessors that seem to take a bare `long` instead of `MemorySegment`. Have you tried pushing segments deeper in the implementation? That way I think you could completely auto-generate this code using jextract. (of course what you have is not bad - I'm mostly trying to see if there's a way to get there w/o all these calls to `MemorySegment::reinterpret`).
>
> To be clear - I'm assuming the `ptr` parameter comes from a single native call. That call returns a pointer to a struct, or maybe an array of structs. If so, we could reinterpret right after the native call, with the right size (the number of structs returned by the native call), and then all the accessors will be just "plain" memory segment accessors, no need to reinterpret (as the segment will already have the correct size).

Each pointer refers to a single struct, not an array.
In this fix I am focused on not using Unsafe.
I don't want the change to go further than that.
The 'long's are retrieved/ passed around/ back down to native in lots of places so it would turn a  focused change into a much bigger change.
grep in java.desktop for "getGlyphImage" to see the tip of the iceberg.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19777#discussion_r1651455679