8348909: [BACKOUT] Implement a better allocator for downcalls

Reviewed-by: shade, liach

Author: JornVernee

src/java.base/share/classes/jdk/internal/foreign/SlicingAllocator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,22 +38,6 @@ public SlicingAllocator(MemorySegment segment) {
         this.segment = segment;
     }
 
-    public long currentOffset() {
-        return sp;
-    }
-
-    public void resetTo(long offset) {
-        if (offset < 0 || offset > sp)
-            throw new IllegalArgumentException(String.format("offset %d should be in [0, %d] ", offset, sp));
-        this.sp = offset;
-    }
-
-    public boolean canAllocate(long byteSize, long byteAlignment) {
-        long min = segment.address();
-        long start = Utils.alignUp(min + sp, byteAlignment) - min;
-        return start + byteSize <= segment.byteSize();
-    }
-
     MemorySegment trySlice(long byteSize, long byteAlignment) {
         long min = segment.address();
         long start = Utils.alignUp(min + sp, byteAlignment) - min;

src/java.base/share/classes/jdk/internal/foreign/abi/BufferStack.java

@@ -382,12 +382,26 @@ static long pickChunkOffset(long chunkOffset, long byteWidth, int chunkWidth) {
                 : chunkOffset;
     }
 
-    private static final int LINKER_STACK_SIZE = Integer.getInteger("jdk.internal.foreign.LINKER_STACK_SIZE", 256);
-    private static final BufferStack LINKER_STACK = new BufferStack(LINKER_STACK_SIZE);
-
-    @ForceInline
     public static Arena newBoundedArena(long size) {
-        return LINKER_STACK.pushFrame(size, 8);
+        return new Arena() {
+            final Arena arena = Arena.ofConfined();
+            final SegmentAllocator slicingAllocator = SegmentAllocator.slicingAllocator(arena.allocate(size));
+
+            @Override
+            public Scope scope() {
+                return arena.scope();
+            }
+
+            @Override
+            public void close() {
+                arena.close();
+            }
+
+            @Override
+            public MemorySegment allocate(long byteSize, long byteAlignment) {
+                return slicingAllocator.allocate(byteSize, byteAlignment);
+            }
+        };
     }
 
     public static Arena newEmptyArena() {