Rework the cleanup a little bit so that we avoid the atomic boolean

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -27,7 +27,6 @@ extension JNISwift2JavaGenerator {
     "org.swift.swiftkit.core.util.*",
     "org.swift.swiftkit.core.collections.*",
     "java.util.*",
-    "java.util.concurrent.atomic.AtomicBoolean",
 
     // NonNull, Unsigned and friends
     "org.swift.swiftkit.core.annotations.*",
@@ -282,6 +281,7 @@ extension JNISwift2JavaGenerator {
         }
         printer.print(
           """
+          this.$cleanup = $createCleanup();
 
           // Only register once we have fully initialized the object since this will need the object pointer.
           swiftArena.register(this);
@@ -317,16 +317,16 @@ extension JNISwift2JavaGenerator {
         /** Pointer to the "self". */
         private final long selfPointer;
 
-        /** Used to track additional state of the underlying object, e.g. if it was explicitly destroyed. */
-        private final AtomicBoolean $state$destroyed = new AtomicBoolean(false);
+        /** Tracks whether this instance has been destroyed; doubles as the destroyed-state holder. */
+        private final SwiftInstanceCleanup $cleanup;
 
         public long $memoryAddress() {
           return this.selfPointer;
         }
 
         @Override
-        public AtomicBoolean $statusDestroyedFlag() {
-          return $state$destroyed;
+        public SwiftInstanceCleanup $cleanup() {
+          return $cleanup;
         }
         """
       )

SwiftKitCore/src/main/java/org/swift/swiftkit/core/AutoSwiftMemorySession.java

@@ -50,7 +50,7 @@ public void register(SwiftInstance instance) {
 
         // We make sure we don't capture `instance` in the
         // cleanup action, so we can ignore the warning below.
-        var cleanupAction = instance.$createCleanup();
+        var cleanupAction = instance.$cleanup();
         swiftCleaner.register(instance, cleanupAction);
     }
 }

SwiftKitCore/src/main/java/org/swift/swiftkit/core/ConfinedSwiftMemorySession.java

@@ -54,7 +54,7 @@ public void close() {
     public void register(SwiftInstance instance) {
         checkValid();
 
-        SwiftInstanceCleanup cleanup = instance.$createCleanup();
+        SwiftInstanceCleanup cleanup = instance.$cleanup();
         this.resources.add(cleanup);
     }
 

SwiftKitCore/src/main/java/org/swift/swiftkit/core/JNISwiftInstance.java

@@ -54,11 +54,13 @@ public interface JNISwiftInstance extends SwiftInstance {
      */
     long $typeMetadataAddress();
 
-    @Override
+    /**
+     * Build a fresh {@link SwiftInstanceCleanup} for this instance.
+     * <p>
+     * Concrete implementations are expected to call this once during construction
+     * and cache the result in a field exposed via {@link #$cleanup()}.
+     */
     default SwiftInstanceCleanup $createCleanup() {
-        return new JNISwiftInstanceCleanup(
-                $createDestroyFunction(),
-                $statusDestroyedFlag()
-        );
+        return new JNISwiftInstanceCleanup($createDestroyFunction());
     }
 }

SwiftKitCore/src/main/java/org/swift/swiftkit/core/JNISwiftInstanceCleanup.java

@@ -14,20 +14,29 @@
 
 package org.swift.swiftkit.core;
 
-import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 
 class JNISwiftInstanceCleanup implements SwiftInstanceCleanup {
+    private static final AtomicIntegerFieldUpdater<JNISwiftInstanceCleanup> DESTROYED =
+            AtomicIntegerFieldUpdater.newUpdater(JNISwiftInstanceCleanup.class, "destroyed");
+
     private final Runnable destroyFunction;
-    private final AtomicBoolean statusDestroyedFlag;
 
-    public JNISwiftInstanceCleanup(Runnable destroyFunction, AtomicBoolean statusDestroyedFlag) {
+    @SuppressWarnings("unused") // accessed via DESTROYED field updater
+    private volatile int destroyed;
+
+    public JNISwiftInstanceCleanup(Runnable destroyFunction) {
         this.destroyFunction = destroyFunction;
-        this.statusDestroyedFlag = statusDestroyedFlag;
+    }
+
+    @Override
+    public boolean isDestroyed() {
+        return destroyed != 0;
     }
 
     @Override
     public void run() {
-        if (statusDestroyedFlag.compareAndSet(false, true)) {
+        if (DESTROYED.compareAndSet(this, 0, 1)) {
             destroyFunction.run();
         } else {
             throw new IllegalStateException("Double destruction attempt detected!");

SwiftKitCore/src/main/java/org/swift/swiftkit/core/SwiftInstance.java

@@ -14,8 +14,6 @@
 
 package org.swift.swiftkit.core;
 
-import java.util.concurrent.atomic.AtomicBoolean;
-
 public interface SwiftInstance {
     /**
      * Pointer to the {@code self} of the underlying Swift object or value.
@@ -27,20 +25,16 @@ public interface SwiftInstance {
     long $memoryAddress();
 
     /**
-     * Called when the arena has decided the value should be destroyed.
+     * Returns the cleanup associated with this instance.
      * <p>
-     * <b>Warning:</b> The cleanup action must not capture {@code this}.
-     */
-    SwiftInstanceCleanup $createCleanup();
-
-    /**
-     * Exposes a boolean value which can be used to indicate if the object was destroyed.
+     * The same cleanup instance is returned on every call. The cleanup also serves as the
+     * destroyed-state holder, allowing callers to poll {@link SwiftInstanceCleanup#isDestroyed()}
+     * even after this instance has been GC-ed.
      * <p>
-     * This is exposing the object, rather than performing the action because we don't want to accidentally
-     * form a strong reference to the {@code SwiftInstance} which could prevent the cleanup from running,
-     * if using an GC managed instance (e.g. using an {@code AutoSwiftMemorySession}.
+     * <b>Warning:</b> The cleanup must not capture {@code this}.
      */
-    AtomicBoolean $statusDestroyedFlag();
+    SwiftInstanceCleanup $cleanup();
+
     /**
      * Ensures that this instance has not been destroyed.
      * <p>
@@ -49,7 +43,7 @@ public interface SwiftInstance {
      * use-after-free errors.
      */
     default void $ensureAlive() {
-        if (this.$statusDestroyedFlag().get()) {
+        if (this.$cleanup().isDestroyed()) {
             throw new IllegalStateException("Attempted to call method on already destroyed instance of " + getClass().getSimpleName() + "!");
         }
     }

SwiftKitCore/src/main/java/org/swift/swiftkit/core/SwiftInstanceCleanup.java

@@ -16,5 +16,13 @@
 
 /**
  * A Swift memory instance cleanup, e.g. count-down a reference count and destroy a class, or destroy struct/enum etc.
+ * <p>
+ * Implementations also serve as the destroyed-state holder for their associated {@link SwiftInstance},
+ * exposing {@link #isDestroyed()} which can be polled even after the instance has been GC-ed.
  */
-public interface SwiftInstanceCleanup extends Runnable {}
+public interface SwiftInstanceCleanup extends Runnable {
+    /**
+     * Whether this cleanup has run, i.e. the associated instance has been destroyed.
+     */
+    boolean isDestroyed();
+}

SwiftKitCore/src/main/java/org/swift/swiftkit/core/collections/SwiftDictionaryMap.java

@@ -15,7 +15,6 @@
 package org.swift.swiftkit.core.collections;
 
 import java.util.*;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.swift.swiftkit.core.*;
 
@@ -33,10 +32,11 @@
 public class SwiftDictionaryMap<K, V> extends AbstractMap<K, V> implements JNISwiftInstance {
 
     private final long selfPointer;
-    private final AtomicBoolean destroyed = new AtomicBoolean(false);
+    private final SwiftInstanceCleanup cleanup;
 
     private SwiftDictionaryMap(long selfPointer) {
         this.selfPointer = selfPointer;
+        this.cleanup = $createCleanup();
     }
 
     public static <K, V> SwiftDictionaryMap<K, V> wrapMemoryAddressUnsafe(long selfPointer, SwiftArena arena) {
@@ -58,8 +58,8 @@ public static <K, V> SwiftDictionaryMap<K, V> wrapMemoryAddressUnsafe(long selfP
     }
 
     @Override
-    public AtomicBoolean $statusDestroyedFlag() {
-        return destroyed;
+    public SwiftInstanceCleanup $cleanup() {
+        return cleanup;
     }
 
     @Override

SwiftKitCore/src/main/java/org/swift/swiftkit/core/collections/SwiftSet.java

@@ -15,7 +15,6 @@
 package org.swift.swiftkit.core.collections;
 
 import java.util.*;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.swift.swiftkit.core.*;
 
@@ -32,10 +31,11 @@
 public class SwiftSet<E> extends AbstractSet<E> implements JNISwiftInstance {
 
     private final long selfPointer;
-    private final AtomicBoolean destroyed = new AtomicBoolean(false);
+    private final SwiftInstanceCleanup cleanup;
 
     private SwiftSet(long selfPointer) {
         this.selfPointer = selfPointer;
+        this.cleanup = $createCleanup();
     }
 
     public static <E> SwiftSet<E> wrapMemoryAddressUnsafe(long selfPointer, SwiftArena arena) {
@@ -57,8 +57,8 @@ public static <E> SwiftSet<E> wrapMemoryAddressUnsafe(long selfPointer, SwiftAre
     }
 
     @Override
-    public AtomicBoolean $statusDestroyedFlag() {
-        return destroyed;
+    public SwiftInstanceCleanup $cleanup() {
+        return cleanup;
     }
 
     @Override

SwiftKitCore/src/test/java/org/swift/swiftkit/AutoArenaTest.java

@@ -17,8 +17,7 @@
 import org.junit.jupiter.api.Test;
 import org.swift.swiftkit.core.JNISwiftInstance;
 import org.swift.swiftkit.core.SwiftArena;
-
-import java.util.concurrent.atomic.AtomicBoolean;
+import org.swift.swiftkit.core.SwiftInstanceCleanup;
 
 public class AutoArenaTest {
 
@@ -29,15 +28,15 @@ public void cleaner_releases_native_resource() {
 
         // This object is registered to the arena.
         var object = new FakeSwiftInstance(arena);
-        var statusDestroyedFlag = object.$statusDestroyedFlag();
+        var cleanup = object.$cleanup();
 
         // Release the object and hope it gets GC-ed soon
 
         // noinspection UnusedAssignment
         object = null;
 
         var i = 1_000;
-        while (!statusDestroyedFlag.get()) {
+        while (!cleanup.isDestroyed()) {
             System.runFinalization();
             System.gc();
 
@@ -48,9 +47,10 @@ public void cleaner_releases_native_resource() {
     }
 
     private static class FakeSwiftInstance implements JNISwiftInstance {
-        AtomicBoolean $state$destroyed = new AtomicBoolean(false);
+        private final SwiftInstanceCleanup cleanup;
 
         public FakeSwiftInstance(SwiftArena arena) {
+            this.cleanup = $createCleanup();
             arena.register(this);
         }
 
@@ -69,8 +69,8 @@ public FakeSwiftInstance(SwiftArena arena) {
         }
 
         @Override
-        public AtomicBoolean $statusDestroyedFlag() {
-            return $state$destroyed;
+        public SwiftInstanceCleanup $cleanup() {
+            return cleanup;
         }
     }
 }

SwiftKitFFM/src/main/java/org/swift/swiftkit/ffm/AllocatingAutoSwiftMemorySession.java

@@ -56,7 +56,7 @@ public void register(SwiftInstance instance) {
 
         // We make sure we don't capture `instance` in the
         // cleanup action, so we can ignore the warning below.
-        var cleanupAction = instance.$createCleanup();
+        var cleanupAction = instance.$cleanup();
         cleaner.register(instance, cleanupAction);
     }
 

SwiftKitFFM/src/main/java/org/swift/swiftkit/ffm/FFMSwiftErrorInstance.java

@@ -18,7 +18,6 @@
 import org.swift.swiftkit.core.SwiftInstanceCleanup;
 
 import java.lang.foreign.MemorySegment;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * Base class for Swift errors passed across the FFM boundary.
@@ -27,17 +26,19 @@
  */
 public abstract class FFMSwiftErrorInstance extends Exception implements SwiftInstance {
     private final MemorySegment memorySegment;
-    private final AtomicBoolean $state$destroyed = new AtomicBoolean(false);
+    private final FFMSwiftInstanceCleanup cleanup;
 
     protected FFMSwiftErrorInstance(String message, MemorySegment segment, AllocatingSwiftArena arena) {
         super(message);
         this.memorySegment = segment;
+        this.cleanup = new FFMSwiftInstanceCleanup(segment, $swiftType());
         arena.register(this);
     }
 
     protected FFMSwiftErrorInstance(MemorySegment segment, AllocatingSwiftArena arena) {
         super();
         this.memorySegment = segment;
+        this.cleanup = new FFMSwiftInstanceCleanup(segment, $swiftType());
         arena.register(this);
     }
 
@@ -50,21 +51,13 @@ protected FFMSwiftErrorInstance(MemorySegment segment, AllocatingSwiftArena aren
         return $memorySegment().address();
     }
 
-    public final AtomicBoolean $statusDestroyedFlag() {
-        return $state$destroyed;
+    @Override
+    public final SwiftInstanceCleanup $cleanup() {
+        return this.cleanup;
     }
 
     /**
      * The Swift type metadata of this type.
      */
     public abstract SwiftAnyType $swiftType();
-
-    @Override
-    public SwiftInstanceCleanup $createCleanup() {
-        return new FFMSwiftInstanceCleanup(
-                $memorySegment(),
-                $swiftType(),
-                $statusDestroyedFlag()
-        );
-    }
 }