RFR: 8337237: Use FFM instead of Unsafe for Java 2D RenderBuffer class

[Maurizio Cimadamore]

On Thu, 25 Jul 2024 22:53:36 GMT, Phil Race <prr at openjdk.org> wrote:

> Migrate from using Unsafe to FFM's MemorySegment API for allocating and setting native memory.
> This code is used by Metal, OpenGL and D3D, so I manually tested SwingSet2 and J2Demo as well as running all the usual tests.
> I also did some micro-benchmarking on the performance of Unsafe vs MemorySegment.
> The performance of either is more than sufficient for us .. ie they could be 10x slower and we wouldn't even notice.
> But they are in the same ballpark, and if one or the other is clearly faster it is the new FFM code.

src/java.desktop/share/classes/sun/java2d/pipe/RenderBuffer.java line 144:

> 142:             int offsetInBytes = offset * SIZEOF_BYTE;
> 143:             int lengthInBytes = length * SIZEOF_BYTE;
> 144:             MemorySegment.copy(x, offsetInBytes, segment, JAVA_BYTE, curOffset, length);

This needs to be fixed too (similar comment as the one @JornVernee left below).

src/java.desktop/share/classes/sun/java2d/pipe/RenderBuffer.java line 274:

> 272:             int offsetInBytes = offset * SIZEOF_LONG;
> 273:             int lengthInBytes = length * SIZEOF_LONG;
> 274:             MemorySegment.copy(x, offsetInBytes, segment, JAVA_LONG, curOffset, length);

This needs fixing too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20339#discussion_r1692713777
PR Review Comment: https://git.openjdk.org/jdk/pull/20339#discussion_r1692715958