RFR: 8334137: Marlin: replace sun.misc.Unsafe memory access methods with FFM [v5]

[Andy Goryachev]

On Mon, 9 Jun 2025 15:13:49 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> PR to replace the use of sun.misc.Unsafe memory access methods in the Marlin rasterizer with FFM.
>> 
>> I broke this up into the following commits. The bulk of the work is in the first two:
>> 
>> 1. Encapsulate all off-heap access in OffHeapArray -- All of the memory allocation and management was already done in the OffHeapArray class, but the users of OffHeapArray, primarily Renderer and RendererNoAA, called Unsafe methods directly. I encapsulated all of the calls to Unsafe in OffHeapArray. The main impact on calling code is that the base address is no longer accessible or needed. Instead, the `(put|get)(Byte|Int)` methods take only an offset. This commit was straight refactoring with no behavioral changes.
>> 2. Initial FFM implementation -- I changed the memory management and access methods to use FFM. Each OffHeap array uses a shared Arena to manage the single memory segment allocated at construction time. The resize method creates a new Arena and memory segment, copying the data from the old and then closing it
>> 3. Set `used` to 0 in `dispose()` -- While testing and instrumenting the code, I discovered that the Renderer dispose methods resize the edges array back to the default size without clearing the "used" field. The used field will be cleared before the next time it is accessed, but clearing it in dispose allows optimizing resize to not copy any data.
>> 4. Remove '--sun-misc-unsafe-memory-access=allow' from test and app execution, since it is no longer needed. This also enables `-Werror` for the `javafx.graphics` module.
>> 5. ~~Temporary debug prints that will be removed before making this "rfr"~~
>> 
>> Additional commits address review comments.
>
> Kevin Rushforth has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review comments

modules/javafx.graphics/src/main/java/com/sun/marlin/OffHeapArray.java line 47:

> 45:     /* members */
> 46:     private MemorySegment segment;
> 47:     private long length;

just curious: why `long`?  are we expecting the length to exceed 2 billion?

modules/javafx.graphics/src/main/java/com/sun/marlin/OffHeapArray.java line 79:

> 77:      * @return number of used bytes
> 78:      */
> 79:     int getUsed() {

wait, length is `long`, but used is `int`?

modules/javafx.graphics/src/main/java/com/sun/marlin/OffHeapArray.java line 97:

> 95:      */
> 96:     void incrementUsed(int increment) {
> 97:         this.used += increment;

if used > 2B, it will overflow, right?

modules/javafx.graphics/src/main/java/com/sun/marlin/OffHeapArray.java line 157:

> 155:         return segment.get(INT_LAYOUT, offset);
> 156:     }
> 157: 

extra newline?

modules/javafx.graphics/src/main/java/com/sun/marlin/Renderer.java line 399:

> 397: 
> 398:         final long SIZE_INT = 4L;
> 399:         long addr   = edgePtr;

minor: extra spaces?

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1814#discussion_r2135938366
PR Review Comment: https://git.openjdk.org/jfx/pull/1814#discussion_r2135942265
PR Review Comment: https://git.openjdk.org/jfx/pull/1814#discussion_r2135943404
PR Review Comment: https://git.openjdk.org/jfx/pull/1814#discussion_r2135946319
PR Review Comment: https://git.openjdk.org/jfx/pull/1814#discussion_r2135947245