8287788: Implement a better allocator for downcalls

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2025, 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
@@ -38,6 +38,22 @@ 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

@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2025, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package jdk.internal.foreign.abi;
+
+import jdk.internal.foreign.SlicingAllocator;
+import jdk.internal.misc.CarrierThreadLocal;
+import jdk.internal.vm.annotation.ForceInline;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.SegmentAllocator;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class BufferStack {
+    private final long size;
+
+    public BufferStack(long size) {
+        this.size = size;
+    }
+
+    private final ThreadLocal<PerThread> tl = new CarrierThreadLocal<>() {
+        @Override
+        protected PerThread initialValue() {
+            return new PerThread(size);
+        }
+    };
+
+    @ForceInline
+    public Arena pushFrame(long size, long byteAlignment) {
+        return tl.get().pushFrame(size, byteAlignment);
+    }
+
+    private static final class PerThread {
+        private final ReentrantLock lock = new ReentrantLock();
+        private final SlicingAllocator stack;
+
+        public PerThread(long size) {
+            this.stack = new SlicingAllocator(Arena.ofAuto().allocate(size));
+        }
+
+        @ForceInline
+        public Arena pushFrame(long size, long byteAlignment) {
+            boolean needsLock = Thread.currentThread().isVirtual() && !lock.isHeldByCurrentThread();
+            if (needsLock && !lock.tryLock()) {
+                // Rare: another virtual thread on the same carrier competed for acquisition.
+                return Arena.ofConfined();
+            }
+            if (!stack.canAllocate(size, byteAlignment)) {
+                if (needsLock) lock.unlock();
+                return Arena.ofConfined();
+            }
+
+            return new Frame(needsLock, size, byteAlignment);
+        }
+
+        private class Frame implements Arena {
+            private final boolean locked;
+            private final long parentOffset;
+            private final long topOfStack;
+            private final Arena scope = Arena.ofConfined();
+            private final SegmentAllocator frame;
+
+            @SuppressWarnings("restricted")
+            public Frame(boolean locked, long byteSize, long byteAlignment) {
+                this.locked = locked;
+
+                parentOffset = stack.currentOffset();
+                MemorySegment frameSegment = stack.allocate(byteSize, byteAlignment);
+                topOfStack = stack.currentOffset();
+                frame = new SlicingAllocator(frameSegment.reinterpret(scope, null));
+            }
+
+            private void assertOrder() {
+                if (topOfStack != stack.currentOffset())
+                    throw new IllegalStateException("Out of order access: frame not top-of-stack");
+            }
+
+            @Override
+            @SuppressWarnings("restricted")
+            public MemorySegment allocate(long byteSize, long byteAlignment) {
+                return frame.allocate(byteSize, byteAlignment);
+            }
+
+            @Override
+            public MemorySegment.Scope scope() {
+                return scope.scope();
+            }
+
+            @Override
+            public void close() {
+                assertOrder();
+                scope.close();
+                stack.resetTo(parentOffset);
+                if (locked) {
+                    lock.unlock();
+                }
+            }
+        }
+    }
+}

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

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

test/jdk/java/foreign/TestBufferStack.java

@@ -0,0 +1,157 @@
+/*
+ * Copyright (c) 2025, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @modules java.base/jdk.internal.foreign.abi
+ * @build NativeTestHelper TestBufferStack
+ * @run testng/othervm --enable-native-access=ALL-UNNAMED TestBufferStack
+ */
+
+import jdk.internal.foreign.abi.BufferStack;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.FunctionDescriptor;
+import java.lang.foreign.MemoryLayout;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.SegmentAllocator;
+import java.lang.invoke.MethodHandle;
+import java.time.Duration;
+import java.util.Arrays;
+import java.util.stream.IntStream;
+
+import static java.lang.foreign.MemoryLayout.structLayout;
+import static java.lang.foreign.ValueLayout.*;
+import static java.time.temporal.ChronoUnit.SECONDS;
+
+public class TestBufferStack extends NativeTestHelper {
+    @Test
+    public void testScopedAllocation() {
+        int stackSize = 128;
+        BufferStack stack = new BufferStack(stackSize);
+        MemorySegment stackSegment;
+        try (Arena frame1 = stack.pushFrame(3 * JAVA_INT.byteSize(), JAVA_INT.byteAlignment())) {
+            // Segments have expected sizes and are accessible and allocated consecutively in the same scope.
+            MemorySegment segment11 = frame1.allocate(JAVA_INT);
+            Assert.assertEquals(segment11.scope(), frame1.scope());
+            Assert.assertEquals(segment11.byteSize(), JAVA_INT.byteSize());
+            segment11.set(JAVA_INT, 0, 1);
+            stackSegment = segment11.reinterpret(stackSize);
+
+            MemorySegment segment12 = frame1.allocate(JAVA_INT);
+            Assert.assertEquals(segment12.address(), segment11.address() + JAVA_INT.byteSize());
+            Assert.assertEquals(segment12.byteSize(), JAVA_INT.byteSize());
+            Assert.assertEquals(segment12.scope(), frame1.scope());
+            segment12.set(JAVA_INT, 0, 1);
+
+            MemorySegment segment2;
+            try (Arena frame2 = stack.pushFrame(JAVA_LONG.byteSize(), JAVA_LONG.byteAlignment())) {
+                Assert.assertNotEquals(frame2.scope(), frame1.scope());
+                // same here, but a new scope.
+                segment2 = frame2.allocate(JAVA_LONG);
+                Assert.assertEquals(segment2.address(), segment12.address() + /*segment12 size + frame 1 spare + alignment constraint*/ 3 * JAVA_INT.byteSize());
+                Assert.assertEquals(segment2.byteSize(), JAVA_LONG.byteSize());
+                Assert.assertEquals(segment2.scope(), frame2.scope());
+                segment2.set(JAVA_LONG, 0, 1);
+
+                // Frames must be closed in stack order.
+                Assert.assertThrows(IllegalStateException.class, frame1::close);
+            }
+            // Scope is closed here, inner segments throw.
+            Assert.assertThrows(IllegalStateException.class, () -> segment2.get(JAVA_INT, 0));
+            // A new stack frame allocates at the same location (but different scope) as the previous did.
+            try (Arena frame3 = stack.pushFrame(2 * JAVA_INT.byteSize(), JAVA_INT.byteAlignment())) {
+                MemorySegment segment3 = frame3.allocate(JAVA_INT);
+                Assert.assertEquals(segment3.scope(), frame3.scope());
+                Assert.assertEquals(segment3.address(), segment12.address() + 2 * JAVA_INT.byteSize());
+            }
+
+            // Fallback arena behaves like regular stack frame.
+            MemorySegment outOfStack;
+            try (Arena hugeFrame = stack.pushFrame(1024, 4)) {
+                outOfStack = hugeFrame.allocate(4);
+                Assert.assertEquals(outOfStack.scope(), hugeFrame.scope());
+                Assert.assertTrue(outOfStack.asOverlappingSlice(stackSegment).isEmpty());
+            }
+            Assert.assertThrows(IllegalStateException.class, () -> outOfStack.get(JAVA_INT, 0));
+
+            // Outer segments are still accessible.
+            segment11.get(JAVA_INT, 0);
+            segment12.get(JAVA_INT, 0);
+        }
+    }
+
+    @Test
+    public void stress() throws InterruptedException {
+        BufferStack stack = new BufferStack(256);
+        Thread[] vThreads = IntStream.range(0, 1024).mapToObj(_ ->
+                Thread.ofVirtual().start(() -> {
+                    long threadId = Thread.currentThread().threadId();
+                    while (!Thread.interrupted()) {
+                        for (int i = 0; i < 1_000_000; i++) {
+                            try (Arena arena = stack.pushFrame(JAVA_LONG.byteSize(), JAVA_LONG.byteAlignment())) {
+                                // Try to assert no two vThreads get allocated the same stack space.
+                                MemorySegment segment = arena.allocate(JAVA_LONG);
+                                JAVA_LONG.varHandle().setVolatile(segment, 0L, threadId);
+                                Assert.assertEquals(threadId, (long) JAVA_LONG.varHandle().getVolatile(segment, 0L));
+                            }
+                        }
+                        Thread.yield(); // make sure the driver thread gets a chance.
+                    }
+                })).toArray(Thread[]::new);
+        Thread.sleep(Duration.of(10, SECONDS));
+        Arrays.stream(vThreads).forEach(
+                thread -> {
+                    Assert.assertTrue(thread.isAlive());
+                    thread.interrupt();
+                });
+    }
+
+    static {
+        System.loadLibrary("TestBufferStack");
+    }
+
+    private static final MemoryLayout HVAPoint3D = structLayout(NativeTestHelper.C_DOUBLE, C_DOUBLE, C_DOUBLE);
+    private static final MemorySegment UPCALL_MH = upcallStub(TestBufferStack.class, "recurse", FunctionDescriptor.of(HVAPoint3D, C_INT));
+    private static final MethodHandle DOWNCALL_MH = downcallHandle("recurse", FunctionDescriptor.of(HVAPoint3D, C_INT, ADDRESS));
+
+    public static MemorySegment recurse(int depth) {
+        try {
+            return (MemorySegment) DOWNCALL_MH.invokeExact((SegmentAllocator) Arena.ofAuto(), depth, UPCALL_MH);
+        } catch (Throwable e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Test
+    public void testDeepStack() throws Throwable {
+        // Each downcall and upcall require 48 bytes of stack.
+        // After five allocations we start falling back.
+        MemorySegment point = recurse(10);
+        Assert.assertEquals(point.getAtIndex(C_DOUBLE, 0), 12.0);
+        Assert.assertEquals(point.getAtIndex(C_DOUBLE, 1), 11.0);
+        Assert.assertEquals(point.getAtIndex(C_DOUBLE, 2), 10.0);
+    }
+}

test/jdk/java/foreign/libTestBufferStack.c

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2025, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "export.h"
+
+typedef struct { double x, y, z; } HVAPoint3D;
+
+EXPORT HVAPoint3D recurse(int depth, HVAPoint3D (*cb)(int)) {
+  if (depth == 0) {
+    HVAPoint3D result = { 2, 1, 0};
+    return result;
+  }
+
+  HVAPoint3D result = cb(depth - 1);
+  result.x += 1;
+  result.y += 1;
+  result.z += 1;
+  return result;
+}