Summary

Enable incremental adoption of MemorySegment VarHandle-based field accessors on the hot path by extending Agrona's buffer hierarchy with DirectBufferEx / MutableDirectBufferEx / AtomicBufferEx interfaces that carry a segment() accessor alongside the existing Unsafe-backed access.

The original goal of replacing UnsafeBuffer with SafeBuffer has evolved. Instead of a full buffer implementation swap, we extend the existing hierarchy so that every buffer in the pipeline exposes its backing MemorySegment via segment() and uses wrapAdjustment() as the index offset into the root segment — enabling zero-allocation segment access on the hot path.

Changes

Buffer type hierarchy

• DirectBufferEx extends DirectBuffer — adds segment(), wrap(DirectBufferEx), wrap(MemorySegment), getBytes(MemorySegment)
• MutableDirectBufferEx extends MutableDirectBuffer, DirectBufferEx — adds putBytes(DirectBufferEx), putBytes(MemorySegment)
• AtomicBufferEx extends AtomicBuffer, MutableDirectBufferEx
• UnsafeBufferEx extends UnsafeBuffer implements AtomicBufferEx — Unsafe-backed with segment overlay
• ExpandableArrayBufferEx extends ExpandableArrayBuffer implements MutableDirectBufferEx — heap expandable
• ExpandableDirectByteBufferEx extends ExpandableDirectByteBuffer implements MutableDirectBufferEx — direct expandable

Zero-allocation hot path

• UnsafeBufferEx / SafeBuffer wrap methods store root backing segment instead of asSlice() per call
• wrapAdjustment() used as index offset into the unsliced segment
• DefaultBufferPool.buffer(slot, offset) uses wrap(DirectBufferEx, offset, length) instead of raw address wrap

Flyweight migration

• Generated Flyweight.wrap / tryWrap / buffer() use DirectBufferEx
• Generated Flyweight.Builder.wrap / buffer() use MutableDirectBufferEx
• Both store segment field via buffer.segment()

Ring buffer path

• MessageConsumer extends MessageHandlerEx (replaces Agrona MessageHandler)
• EngineWorker uses streamsBuffer.readEx() delivering MutableDirectBufferEx

Codebase-wide type migration

• ~400+ files migrated from DirectBuffer / MutableDirectBuffer to Ex variants
• AtomicBuffer → AtomicBufferEx where assigned UnsafeBufferEx
• ExpandableArrayBuffer / ExpandableDirectByteBuffer → Ex variants

References

• SafeBuffer: AtomicBuffer implementation backed by MemorySegment #1719 — SafeBuffer backed by MemorySegment FFM API
• feat(engine): add SafeBuffer backed by MemorySegment FFM API #1720 — feat(engine): add SafeBuffer backed by MemorySegment FFM API