8317819: Scope should reflect lifetime of underying resource (mainline)

Reviewed-by: jvernee

src/java.base/share/classes/java/lang/foreign/Arena.java

@@ -43,9 +43,10 @@ import java.lang.foreign.MemorySegment.Scope;
  * to obtain native segments.
  * <p>
  * The simplest arena is the {@linkplain Arena#global() global arena}. The global arena
- * features an <em>unbounded lifetime</em>. As such, native segments allocated with the global arena are always
+ * features an <em>unbounded lifetime</em>. The scope of the global arena is the global scope.
- * accessible and their backing regions of memory are never deallocated. Moreover, memory segments allocated with the
+ * As such, native segments allocated with the global arena are always accessible and their backing regions
- * global arena can be {@linkplain MemorySegment#isAccessibleBy(Thread) accessed} from any thread.
+ * of memory are never deallocated.
+ * Moreover, memory segments allocated with the global arena can be {@linkplain MemorySegment#isAccessibleBy(Thread) accessed} from any thread.
  * {@snippet lang = java:
  * MemorySegment segment = Arena.global().allocate(100, 1); // @highlight regex='global()'
  * ...
@@ -53,7 +54,8 @@ import java.lang.foreign.MemorySegment.Scope;
  *}
  * <p>
  * Alternatively, clients can obtain an {@linkplain Arena#ofAuto() automatic arena}, that is an arena
- * which features a <em>bounded lifetime</em> that is managed, automatically, by the garbage collector. As such, the regions
+ * which features a <em>bounded lifetime</em> that is managed, automatically, by the garbage collector. The scope
+ * of an automatic arena is an automatic scope. As such, the regions
  * of memory backing memory segments allocated with the automatic arena are deallocated at some unspecified time
  * <em>after</em> the automatic arena (and all the segments allocated by it) becomes
  * <a href="../../../java/lang/ref/package.html#reachability">unreachable</a>, as shown below:
@@ -67,11 +69,9 @@ import java.lang.foreign.MemorySegment.Scope;
  * Rather than leaving deallocation in the hands of the Java runtime, clients will often wish to exercise control over
  * the timing of deallocation for regions of memory that back memory segments. Two kinds of arenas support this,
  * namely {@linkplain #ofConfined() confined} and {@linkplain #ofShared() shared} arenas. They both feature
- * bounded lifetimes that are managed manually. For instance, the lifetime of a confined arena starts when the confined
+ * bounded lifetimes that are managed manually. For instance, when a confined arena is {@linkplain #close() closed}
- * arena is created, and ends when the confined arena is {@linkplain #close() closed}. As a result, the regions of memory
+ * successfully, its scope is {@linkplain Scope#isAlive() invalidated}. As a result, all the memory segments allocated
- * backing memory segments allocated with a confined arena are deallocated when the confined arena is closed.
+ * by the arena can no longer be accessed, and their regions of memory are deallocated:
- * When this happens, all the segments allocated with the confined arena are invalidated, and subsequent access
- * operations on these segments will fail {@link IllegalStateException}:
  *
  * {@snippet lang = java:
  * MemorySegment segment = null;
@@ -219,7 +219,7 @@ public interface Arena extends SegmentAllocator, AutoCloseable {
      */
     static Arena global() {
         class Holder {
-            static final Arena GLOBAL = MemorySessionImpl.GLOBAL.asArena();
+            static final Arena GLOBAL = MemorySessionImpl.GLOBAL_SESSION.asArena();
         }
         return Holder.GLOBAL;
     }

src/java.base/share/classes/java/lang/foreign/Linker.java

@@ -365,7 +365,7 @@ import java.util.stream.Stream;
  *
  * The size of the segment returned by the {@code malloc} downcall method handle is
  * <a href="MemorySegment.html#wrapping-addresses">zero</a>. Moreover, the scope of the
- * returned segment is a fresh scope that is always alive. To provide safe access to the segment, we must,
+ * returned segment is the global scope. To provide safe access to the segment, we must,
  * unsafely, resize the segment to the desired size (100, in this case). It might also be desirable to
  * attach the segment to some existing {@linkplain Arena arena}, so that the lifetime of the region of memory
  * backing the segment can be managed automatically, as for any other native segment created directly from Java code.
@@ -563,7 +563,7 @@ public sealed interface Linker permits AbstractLinker {
      * <p>
      * Moreover, if the provided function descriptor's return layout is an {@linkplain AddressLayout address layout},
      * invoking the returned method handle will return a native segment associated with
-     * a fresh scope that is always alive. Under normal conditions, the size of the returned segment is {@code 0}.
+     * the global scope. Under normal conditions, the size of the returned segment is {@code 0}.
      * However, if the function descriptor's return layout has a {@linkplain AddressLayout#targetLayout() target layout}
      * {@code T}, then the size of the returned segment is set to {@code T.byteSize()}.
      * <p>
@@ -602,7 +602,7 @@ public sealed interface Linker permits AbstractLinker {
      * upcall stub segment will be deallocated when the provided confined arena is {@linkplain Arena#close() closed}.
      * <p>
      * An upcall stub argument whose corresponding layout is an {@linkplain AddressLayout address layout}
-     * is a native segment associated with a fresh scope that is always alive.
+     * is a native segment associated with the global scope.
      * Under normal conditions, the size of this segment argument is {@code 0}.
      * However, if the address layout has a {@linkplain AddressLayout#targetLayout() target layout} {@code T}, then the size of the
      * segment argument is set to {@code T.byteSize()}.

src/java.base/share/classes/java/lang/foreign/MemoryLayout.java

@@ -492,8 +492,8 @@ public sealed interface MemoryLayout permits SequenceLayout, GroupLayout, Paddin
      * </ul>
      * <p>
      * If the selected layout is an {@linkplain AddressLayout address layout}, calling {@link VarHandle#get(Object...)}
-     * on the returned var handle will return a new memory segment. The segment is associated with a fresh scope that is
+     * on the returned var handle will return a new memory segment. The segment is associated with the global scope.
-     * always alive. Moreover, the size of the segment depends on whether the address layout has a
+     * Moreover, the size of the segment depends on whether the address layout has a
      * {@linkplain AddressLayout#targetLayout() target layout}. More specifically:
      * <ul>
      *     <li>If the address layout has a target layout {@code T}, then the size of the returned segment
@@ -513,7 +513,7 @@ public sealed interface MemoryLayout permits SequenceLayout, GroupLayout, Paddin
      * {@snippet lang = "java":
      * VarHandle baseHandle = this.varHandle(P);
      * MemoryLayout target = ((AddressLayout)this.select(P)).targetLayout().get();
-     * VarHandle targetHandle = target.varHandle(P');
+     * VarHandle targetHandle = target.varHandle(P);
      * targetHandle = MethodHandles.insertCoordinates(targetHandle, 1, 0L); // always access nested targets at offset 0
      * targetHandle = MethodHandles.collectCoordinates(targetHandle, 0,
      *         baseHandle.toMethodHandle(VarHandle.AccessMode.GET));

src/java.base/share/classes/java/lang/foreign/MemorySegment.java

@@ -376,7 +376,7 @@ import jdk.internal.vm.annotation.ForceInline;
  *     of memory whose size is not known, any access operations involving these segments cannot be validated.
  *     In effect, a zero-length memory segment <em>wraps</em> an address, and it cannot be used without explicit intent
  *     (see below);</li>
- *     <li>The segment is associated with a fresh scope that is always alive. Thus, while zero-length
+ *     <li>The segment is associated with the global scope. Thus, while zero-length
  *     memory segments cannot be accessed directly, they can be passed, opaquely, to other pointer-accepting foreign functions.</li>
  * </ul>
  * <p>
@@ -625,7 +625,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
      * MemorySegment cleanupSegment = MemorySegment.ofAddress(this.address())
      *                                             .reinterpret(byteSize());
      * }
-     * That is, the cleanup action receives a segment that is associated with a fresh scope that is always alive,
+     * That is, the cleanup action receives a segment that is associated with the global scope,
      * and is accessible from any thread. The size of the segment accepted by the cleanup action is {@link #byteSize()}.
      * <p>
      * This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
@@ -664,7 +664,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
      * MemorySegment cleanupSegment = MemorySegment.ofAddress(this.address())
      *                                             .reinterpret(newSize);
      * }
-     * That is, the cleanup action receives a segment that is associated with a fresh scope that is always alive,
+     * That is, the cleanup action receives a segment that is associated with the global scope,
      * and is accessible from any thread. The size of the segment accepted by the cleanup action is {@code newSize}.
      * <p>
      * This method is <a href="package-summary.html#restricted"><em>restricted</em></a>.
@@ -1155,11 +1155,9 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
      * <p>
      * If the provided buffer has been obtained by calling {@link #asByteBuffer()} on a memory segment whose
      * {@linkplain Scope scope} is {@code S}, the returned segment will be associated with the
-     * same scope {@code S}. Otherwise, the scope of the returned segment is a fresh scope that is always alive.
+     * same scope {@code S}. Otherwise, the scope of the returned segment is an automatic scope that keeps the provided
-     * <p>
+     * buffer reachable. As such, if the provided buffer is a direct buffer, its backing memory region will not be
-     * The scope associated with the returned segment keeps the provided buffer reachable. As such, if
+     * deallocated as long as the returned segment (or any of its slices) are kept reachable.
-     * the provided buffer is a direct buffer, its backing memory region will not be deallocated as long as the
-     * returned segment (or any of its slices) are kept reachable.
      *
      * @param buffer the buffer instance to be turned into a new memory segment.
      * @return a memory segment, derived from the given buffer instance.
@@ -1174,7 +1172,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given byte array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param byteArray the primitive array backing the heap memory segment.
@@ -1186,7 +1184,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given char array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param charArray the primitive array backing the heap segment.
@@ -1198,7 +1196,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given short array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param shortArray the primitive array backing the heap segment.
@@ -1210,7 +1208,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given int array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param intArray the primitive array backing the heap segment.
@@ -1222,7 +1220,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given float array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param floatArray the primitive array backing the heap segment.
@@ -1234,7 +1232,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given long array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param longArray the primitive array backing the heap segment.
@@ -1246,7 +1244,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a heap segment backed by the on-heap region of memory that holds the given double array.
-     * The scope of the returned segment is a fresh scope that is always alive, and keeps the given array reachable.
+     * The scope of the returned segment is an automatic scope that keeps the given array reachable.
      * The returned segment is always accessible, from any thread. Its {@link #address()} is set to zero.
      *
      * @param doubleArray the primitive array backing the heap segment.
@@ -1263,7 +1261,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Creates a zero-length native segment from the given {@linkplain #address() address value}.
-     * The returned segment is associated with a scope that is always alive, and is accessible from any thread.
+     * The returned segment is associated with the global scope, and is accessible from any thread.
      * <p>
      * On 32-bit platforms, the given address value will be normalized such that the
      * highest-order ("leftmost") 32 bits of the {@link MemorySegment#address() address}
@@ -1642,7 +1640,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Reads an address from this segment at the given offset, with the given layout. The read address is wrapped in
-     * a native segment, associated with a fresh scope that is always alive. Under normal conditions,
+     * a native segment, associated with the global scope. Under normal conditions,
      * the size of the returned segment is {@code 0}. However, if the provided address layout has a
      * {@linkplain AddressLayout#targetLayout() target layout} {@code T}, then the size of the returned segment
      * is set to {@code T.byteSize()}.
@@ -1994,7 +1992,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * Reads an address from this segment at the given at the given index, scaled by the given layout size. The read address is wrapped in
-     * a native segment, associated with a fresh scope that is always alive. Under normal conditions,
+     * a native segment, associated with the global scope. Under normal conditions,
      * the size of the returned segment is {@code 0}. However, if the provided address layout has a
      * {@linkplain AddressLayout#targetLayout() target layout} {@code T}, then the size of the returned segment
      * is set to {@code T.byteSize()}.
@@ -2192,11 +2190,38 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
 
     /**
      * A scope models the <em>lifetime</em> of all the memory segments associated with it. That is, a memory segment
-     * cannot be accessed if its associated scope is not {@linkplain #isAlive() alive}. A new scope is typically
+     * cannot be accessed if its associated scope is not {@linkplain #isAlive() alive}. Scope instances can be compared
-     * obtained indirectly, by creating a new {@linkplain Arena arena}.
+     * for equality. That is, two scopes are considered {@linkplain #equals(Object) equal} if they denote the same lifetime.
      * <p>
-     * Scope instances can be compared for equality. That is, two scopes
+     * The lifetime of a memory segment can be either <em>unbounded</em> or <em>bounded</em>. An unbounded lifetime
-     * are considered {@linkplain #equals(Object)} if they denote the same lifetime.
+     * is modelled with the <em>global scope</em>. The global scope is always {@link #isAlive() alive}. As such, a segment
+     * associated with the global scope features trivial temporal bounds, and is always accessible.
+     * Segments associated with the global scope are:
+     * <ul>
+     *     <li>Segments obtained from the {@linkplain Arena#global() global arena};</li>
+     *     <li>Segments obtained from a raw address, using the {@link MemorySegment#ofAddress(long)} factory; and</li>
+     *     <li><a href="#wrapping-addresses">Zero-length memory segments.</a></li>
+     * </ul>
+     * <p>
+     * Conversely, a bounded lifetime is modelled with a segment scope that can be invalidated, either {@link Arena#close() explicitly},
+     * or automatically, by the garbage collector. A segment scope that is invalidated automatically is an <em>automatic scope</em>.
+     * An automatic scope is always {@link #isAlive() alive} as long as it is <a href="../../../java/lang/ref/package.html#reachability">reachable</a>.
+     * Segments associated with an automatic scope are:
+     * <ul>
+     *     <li>Segments obtained from an {@linkplain Arena#ofAuto() automatic arena};</li>
+     *     <li>Segments obtained from a Java array, e.g. using the {@link MemorySegment#ofArray(int[])} factory;</li>
+     *     <li>Segments obtained from a buffer, using the {@link MemorySegment#ofBuffer(Buffer)} factory; and</li>
+     *     <li>Segments obtained from {@linkplain SymbolLookup#loaderLookup() loader lookup}.</li>
+     * </ul>
+     * If two memory segments are obtained from the same {@linkplain #ofBuffer(Buffer) buffer}
+     * or {@linkplain #ofArray(int[]) array}, the automatic scopes associated with said segments are considered
+     * {@linkplain #equals(Object) equal}, as the two segments have the same lifetime:
+     * {@snippet lang=java :
+     * byte[] arr = new byte[10];
+     * MemorySegment segment1 = MemorySegment.ofArray(arr);
+     * MemorySegment segment2 = MemorySegment.ofArray(arr);
+     * assert segment1.scope().equals(segment2.scope());
+     * }
      */
     sealed interface Scope permits MemorySessionImpl {
         /**

src/java.base/share/classes/java/lang/foreign/SymbolLookup.java

@@ -165,7 +165,7 @@ public interface SymbolLookup {
      * <p>
      * Libraries associated with a class loader are unloaded when the class loader becomes
      * <a href="../../../java/lang/ref/package.html#reachability">unreachable</a>. The symbol lookup
-     * returned by this method is associated with a fresh {@linkplain MemorySegment.Scope scope} which keeps the caller's
+     * returned by this method is associated with an automatic {@linkplain MemorySegment.Scope scope} which keeps the caller's
      * class loader reachable. Therefore, libraries associated with the caller's class loader are kept loaded
      * (and their symbols available) as long as a loader lookup for that class loader, or any of the segments
      * obtained by it, is reachable.
@@ -189,7 +189,7 @@ public interface SymbolLookup {
         if ((loader == null || loader instanceof BuiltinClassLoader)) {
             loaderArena = Arena.global();
         } else {
-            MemorySessionImpl session = MemorySessionImpl.heapSession(loader);
+            MemorySessionImpl session = MemorySessionImpl.createHeap(loader);
             loaderArena = session.asArena();
         }
         return name -> {

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

@@ -55,6 +55,7 @@ import jdk.internal.reflect.Reflection;
 import jdk.internal.util.ArraysSupport;
 import jdk.internal.util.Preconditions;
 import jdk.internal.vm.annotation.ForceInline;
+import sun.nio.ch.DirectBuffer;
 
 import static java.lang.foreign.ValueLayout.JAVA_BYTE;
 
@@ -556,7 +557,7 @@ public abstract sealed class AbstractMemorySegmentImpl
         if (bufferSegment != null) {
             bufferScope = bufferSegment.scope;
         } else {
-            bufferScope = MemorySessionImpl.heapSession(bb);
+            bufferScope = MemorySessionImpl.createHeap(bufferRef(bb));
         }
         if (base != null) {
             if (base instanceof byte[]) {
@@ -584,6 +585,17 @@ public abstract sealed class AbstractMemorySegmentImpl
         }
     }
 
+    private static Object bufferRef(Buffer buffer) {
+        if (buffer instanceof DirectBuffer directBuffer) {
+            // direct buffer, return either the buffer attachment (for slices and views), or the buffer itself
+            return directBuffer.attachment() != null ?
+                    directBuffer.attachment() : directBuffer;
+        } else {
+            // heap buffer, return the underlying array
+            return NIO_ACCESS.getBufferBase(buffer);
+        }
+    }
+
     private static int getScaleFactor(Buffer buffer) {
         if (buffer instanceof ByteBuffer) {
             return 0;

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

@@ -25,20 +25,23 @@
 
 package jdk.internal.foreign;
 
+import jdk.internal.access.JavaNioAccess;
+import jdk.internal.access.SharedSecrets;
 import jdk.internal.vm.annotation.ForceInline;
+import sun.nio.ch.DirectBuffer;
+
+import java.nio.Buffer;
+import java.util.Objects;
 
 /**
  * The global, non-closeable, shared session. Similar to a shared session, but its {@link #close()} method throws unconditionally.
  * Adding new resources to the global session, does nothing: as the session can never become not-alive, there is nothing to track.
  * Acquiring and or releasing a memory session similarly does nothing.
  */
-final class GlobalSession extends MemorySessionImpl {
+non-sealed class GlobalSession extends MemorySessionImpl {
 
-    final Object ref;
+    public GlobalSession() {
-
-    public GlobalSession(Object ref) {
         super(null, null);
-        this.ref = ref;
     }
 
     @Override
@@ -67,4 +70,32 @@ final class GlobalSession extends MemorySessionImpl {
     public void justClose() {
         throw nonCloseable();
     }
+
+    /**
+     * This is a global session that wraps a heap object. Possible objects are: Java arrays, buffers and
+     * class loaders. Objects of two heap sessions are compared by identity. That is, if the wrapped object is the same,
+     * then the resulting heap sessions are also considered equals. We do not compare the objects using
+     * {@link Object#equals(Object)}, as that would be problematic when comparing buffers, whose equality and
+     * hash codes are content-dependent.
+     */
+    static class HeapSession extends GlobalSession {
+
+        final Object ref;
+
+        public HeapSession(Object ref) {
+            super();
+            this.ref = Objects.requireNonNull(ref);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return obj instanceof HeapSession session &&
+                    ref == session.ref;
+        }
+
+        @Override
+        public int hashCode() {
+            return System.identityHashCode(ref);
+        }
+    }
 }

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

@@ -48,8 +48,7 @@ final class MappedMemorySegmentImpl extends NativeMemorySegmentImpl {
 
     @Override
     ByteBuffer makeByteBuffer() {
-        return NIO_ACCESS.newMappedByteBuffer(unmapper, min, (int)length, null,
+        return NIO_ACCESS.newMappedByteBuffer(unmapper, min, (int)length, null, this);
-                scope == MemorySessionImpl.GLOBAL ? null : this);
     }
 
     @Override

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

@@ -33,6 +33,8 @@ import java.lang.invoke.MethodHandles;
 import java.lang.invoke.VarHandle;
 import java.lang.ref.Cleaner;
 import java.util.Objects;
+
+import jdk.internal.foreign.GlobalSession.HeapSession;
 import jdk.internal.misc.ScopedMemoryAccess;
 import jdk.internal.vm.annotation.ForceInline;
 
@@ -59,10 +61,10 @@ public abstract sealed class MemorySessionImpl
     static final VarHandle STATE;
     static final int MAX_FORKS = Integer.MAX_VALUE;
 
-    public static final MemorySessionImpl GLOBAL = new GlobalSession(null);
-
     static final ScopedMemoryAccess.ScopedAccessError ALREADY_CLOSED = new ScopedMemoryAccess.ScopedAccessError(MemorySessionImpl::alreadyClosed);
     static final ScopedMemoryAccess.ScopedAccessError WRONG_THREAD = new ScopedMemoryAccess.ScopedAccessError(MemorySessionImpl::wrongThread);
+    // This is the session of all zero-length memory segments
+    public static final MemorySessionImpl GLOBAL_SESSION = new GlobalSession();
 
     final ResourceList resourceList;
     final Thread owner;
@@ -143,6 +145,10 @@ public abstract sealed class MemorySessionImpl
         return new ImplicitSession(cleaner);
     }
 
+    public static MemorySessionImpl createHeap(Object ref) {
+        return new HeapSession(ref);
+    }
+
     public abstract void release0();
 
     public abstract void acquire0();
@@ -230,10 +236,6 @@ public abstract sealed class MemorySessionImpl
 
     abstract void justClose();
 
-    public static MemorySessionImpl heapSession(Object ref) {
-        return new GlobalSession(ref);
-    }
-
     /**
      * A list of all cleanup actions associated with a memory session. Cleanup actions are modelled as instances
      * of the {@link ResourceCleanup} class, and, together, form a linked list. Depending on whether a session

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

@@ -69,8 +69,7 @@ sealed class NativeMemorySegmentImpl extends AbstractMemorySegmentImpl permits M
 
     @Override
     ByteBuffer makeByteBuffer() {
-        return NIO_ACCESS.newDirectByteBuffer(min, (int) this.length, null,
+        return NIO_ACCESS.newDirectByteBuffer(min, (int) this.length, null, this);
-                scope == MemorySessionImpl.GLOBAL ? null : this);
     }
 
     @Override

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

@@ -77,7 +77,7 @@ public class SegmentFactories {
     @ForceInline
     public static MemorySegment makeNativeSegmentUnchecked(long min, long byteSize) {
         ensureInitialized();
-        return new NativeMemorySegmentImpl(min, byteSize, false, new GlobalSession(null));
+        return new NativeMemorySegmentImpl(min, byteSize, false, MemorySessionImpl.GLOBAL_SESSION);
     }
 
     public static MemorySegment fromArray(byte[] arr) {
@@ -85,7 +85,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_BYTE_INDEX_SCALE;
         return new OfByte(Unsafe.ARRAY_BYTE_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(short[] arr) {
@@ -93,7 +93,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_SHORT_INDEX_SCALE;
         return new OfShort(Unsafe.ARRAY_SHORT_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(int[] arr) {
@@ -101,7 +101,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_INT_INDEX_SCALE;
         return new OfInt(Unsafe.ARRAY_INT_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(char[] arr) {
@@ -109,7 +109,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_CHAR_INDEX_SCALE;
         return new OfChar(Unsafe.ARRAY_CHAR_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(float[] arr) {
@@ -117,7 +117,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_FLOAT_INDEX_SCALE;
         return new OfFloat(Unsafe.ARRAY_FLOAT_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(double[] arr) {
@@ -125,7 +125,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_DOUBLE_INDEX_SCALE;
         return new OfDouble(Unsafe.ARRAY_DOUBLE_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment fromArray(long[] arr) {
@@ -133,7 +133,7 @@ public class SegmentFactories {
         Objects.requireNonNull(arr);
         long byteSize = (long)arr.length * Unsafe.ARRAY_LONG_INDEX_SCALE;
         return new OfLong(Unsafe.ARRAY_LONG_BASE_OFFSET, arr, byteSize, false,
-                MemorySessionImpl.heapSession(arr));
+                MemorySessionImpl.createHeap(arr));
     }
 
     public static MemorySegment allocateSegment(long byteSize, long byteAlignment, MemorySessionImpl sessionImpl,

test/jdk/java/foreign/TestScope.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 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
+ * 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
+ * @run testng/othervm --enable-native-access=ALL-UNNAMED TestScope
+ */
+
+import org.testng.annotations.*;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.SymbolLookup;
+import java.nio.ByteBuffer;
+import java.nio.IntBuffer;
+
+import static org.testng.Assert.*;
+
+public class TestScope {
+
+    static {
+        System.loadLibrary("LookupTest");
+    }
+
+    @Test
+    public void testDifferentArrayScope() {
+        MemorySegment.Scope scope1 = MemorySegment.ofArray(new byte[10]).scope();
+        MemorySegment.Scope scope2 = MemorySegment.ofArray(new byte[10]).scope();
+        assertNotEquals(scope1, scope2);
+    }
+
+    @Test
+    public void testDifferentBufferScope() {
+        MemorySegment.Scope scope1 = MemorySegment.ofBuffer(ByteBuffer.allocateDirect(10)).scope();
+        MemorySegment.Scope scope2 = MemorySegment.ofBuffer(ByteBuffer.allocateDirect(10)).scope();
+        assertNotEquals(scope1, scope2);
+    }
+
+    @Test
+    public void testDifferentArenaScope() {
+        MemorySegment.Scope scope1 = Arena.ofAuto().allocate(10).scope();
+        MemorySegment.Scope scope2 = Arena.ofAuto().allocate(10).scope();
+        assertNotEquals(scope1, scope2);
+    }
+
+    @Test
+    public void testSameArrayScope() {
+        byte[] arr = new byte[10];
+        assertEquals(MemorySegment.ofArray(arr).scope(), MemorySegment.ofArray(arr).scope());
+        ByteBuffer buf = ByteBuffer.wrap(arr);
+        assertEquals(MemorySegment.ofArray(arr).scope(), MemorySegment.ofBuffer(buf).scope());
+        testDerivedBufferScope(MemorySegment.ofArray(arr));
+    }
+
+    @Test
+    public void testSameBufferScope() {
+        ByteBuffer buf = ByteBuffer.allocateDirect(10);
+        assertEquals(MemorySegment.ofBuffer(buf).scope(), MemorySegment.ofBuffer(buf).scope());
+        testDerivedBufferScope(MemorySegment.ofBuffer(buf));
+    }
+
+    @Test
+    public void testSameArenaScope() {
+        try (Arena arena = Arena.ofConfined()) {
+            MemorySegment segment1 = arena.allocate(10);
+            MemorySegment segment2 = arena.allocate(10);
+            assertEquals(segment1.scope(), segment2.scope());
+            testDerivedBufferScope(segment1);
+        }
+    }
+
+    @Test
+    public void testSameNativeScope() {
+        MemorySegment segment1 = MemorySegment.ofAddress(42);
+        MemorySegment segment2 = MemorySegment.ofAddress(43);
+        assertEquals(segment1.scope(), segment2.scope());
+        assertEquals(segment1.scope(), segment2.reinterpret(10).scope());
+        assertEquals(segment1.scope(), Arena.global().scope());
+        testDerivedBufferScope(segment1.reinterpret(10));
+    }
+
+    @Test
+    public void testSameLookupScope() {
+        SymbolLookup loaderLookup = SymbolLookup.loaderLookup();
+        MemorySegment segment1 = loaderLookup.find("f").get();
+        MemorySegment segment2 = loaderLookup.find("c").get();
+        assertEquals(segment1.scope(), segment2.scope());
+        testDerivedBufferScope(segment1.reinterpret(10));
+    }
+
+    void testDerivedBufferScope(MemorySegment segment) {
+        ByteBuffer buffer = segment.asByteBuffer();
+        MemorySegment.Scope expectedScope = segment.scope();
+        assertEquals(MemorySegment.ofBuffer(buffer).scope(), expectedScope);
+        // buffer slices should have same scope
+        ByteBuffer slice = buffer.slice(0, 2);
+        assertEquals(expectedScope, MemorySegment.ofBuffer(slice).scope());
+        // buffer views should have same scope
+        IntBuffer view = buffer.asIntBuffer();
+        assertEquals(expectedScope, MemorySegment.ofBuffer(view).scope());
+    }
+}