fix multithreading of system/observer callback + use valueLayout of java

Author: elebras1

examples/src/main/java/com/github/elebras1/flecs/examples/AdvancedSystemExample.java

@@ -46,7 +46,7 @@ public static void main(String[] args) {
                 .with(posId)
                 .rate(2)
                 .kind(FlecsConstants.EcsOnUpdate)
-                .run(it -> {
+                .iter(it -> {
                     System.out.println("  [Rate Filter] Running every 2nd frame (matched: " + it.count() + " entities)");
                 });
 
@@ -69,12 +69,13 @@ public static void main(String[] args) {
                     for (int i = 0; i < it.count(); i++) {
                         Position pos = positions.get(i);
                         Velocity vel = velocities.get(i);
-                        
+
                         float newX = pos.x() + vel.dx() * it.deltaTime();
                         float newY = pos.y() + vel.dy() * it.deltaTime();
                         long entityId = it.entity(i);
                         Entity entity = world.obtainEntity(entityId);
                         entity.set(new Position(newX, newY));
+                        // Note: System.out.printf removed to avoid synchronization issues with multi-threading
                     }
                 });
 

src/main/java/com/github/elebras1/flecs/Iter.java

@@ -1,6 +1,7 @@
 package com.github.elebras1.flecs;
 
 import java.lang.foreign.MemorySegment;
+import java.lang.foreign.ValueLayout;
 
 public class Iter {
 
@@ -36,7 +37,7 @@ public long entityId(int index) {
             throw new IndexOutOfBoundsException("Index " + index + " out of bounds for count " + this.count());
         }
         MemorySegment entities = ecs_iter_t.entities(this.nativeIter);
-        return entities.getAtIndex(flecs_h$shared.C_LONG, index);
+        return entities.getAtIndex(ValueLayout.JAVA_LONG, index);
     }
 
     public long entity(int index) {
@@ -86,7 +87,7 @@ public long termId(int index) {
             return 0;
         }
 
-        return ids.getAtIndex(flecs_h$shared.C_LONG, index);
+        return ids.getAtIndex(ValueLayout.JAVA_LONG, index);
     }
 
     public int fieldSize(int index) {
@@ -99,7 +100,7 @@ public int fieldSize(int index) {
             return 0;
         }
 
-        return sizes.getAtIndex(flecs_h$shared.C_INT, index);
+        return sizes.getAtIndex(ValueLayout.JAVA_INT, index);
     }
 
     public int fieldCount() {

src/main/java/com/github/elebras1/flecs/ObserverBuilder.java

@@ -159,14 +159,16 @@ public ObserverBuilder observerFlags(int flags) {
     public FlecsObserver iter(Query.IterCallback callback) {
         this.iterCallback = callback;
 
-        final Iter[] iterHolder = new Iter[1];
+        final ThreadLocal<Iter> iterHolder = new ThreadLocal<>();
         MemorySegment callbackStub = ecs_iter_action_t.allocate(it -> {
-            if (iterHolder[0] == null) {
-                iterHolder[0] = new Iter(it, this.world);
+            Iter iter = iterHolder.get();
+            if (iter == null) {
+                iter = new Iter(it, this.world);
+                iterHolder.set(iter);
             } else {
-                iterHolder[0].setNativeIter(it);
+                iter.setNativeIter(it);
             }
-            callback.accept(iterHolder[0]);
+            callback.accept(iter);
         }, this.world.arena());
 
         ecs_observer_desc_t.callback(this.desc, callbackStub);
@@ -177,14 +179,16 @@ public FlecsObserver iter(Query.IterCallback callback) {
     public FlecsObserver run(Query.RunCallback callback) {
         this.runCallback = callback;
 
-        final Iter[] iterHolder = new Iter[1];
+        final ThreadLocal<Iter> iterHolder = new ThreadLocal<>();
         MemorySegment callbackStub = ecs_run_action_t.allocate(it -> {
-            if (iterHolder[0] == null) {
-                iterHolder[0] = new Iter(it, this.world);
+            Iter iter = iterHolder.get();
+            if (iter == null) {
+                iter = new Iter(it, this.world);
+                iterHolder.set(iter);
             } else {
-                iterHolder[0].setNativeIter(it);
+                iter.setNativeIter(it);
             }
-            callback.accept(iterHolder[0]);
+            callback.accept(iter);
         }, this.world.arena());
 
         ecs_observer_desc_t.run(this.desc, callbackStub);

src/main/java/com/github/elebras1/flecs/SystemBuilder.java

@@ -187,14 +187,9 @@ public <T> SystemBuilder read(Class<T> componentClass) {
     public FlecsSystem iter(Query.IterCallback callback) {
         this.iterCallback = callback;
 
-        final Iter[] iterHolder = new Iter[1];
         MemorySegment callbackStub = ecs_iter_action_t.allocate(it -> {
-            if (iterHolder[0] == null) {
-                iterHolder[0] = new Iter(it, this.world);
-            } else {
-                iterHolder[0].setNativeIter(it);
-            }
-            callback.accept(iterHolder[0]);
+            Iter iter = new Iter(it, this.world);
+            callback.accept(iter);
         }, this.world.arena());
 
         ecs_system_desc_t.callback(this.desc, callbackStub);
@@ -205,14 +200,16 @@ public FlecsSystem iter(Query.IterCallback callback) {
     public FlecsSystem run(Query.RunCallback callback) {
         this.runCallback = callback;
 
-        final Iter[] iterHolder = new Iter[1];
+        final ThreadLocal<Iter> iterHolder = new ThreadLocal<>();
         MemorySegment callbackStub = ecs_run_action_t.allocate(it -> {
-            if (iterHolder[0] == null) {
-                iterHolder[0] = new Iter(it, this.world);
+            Iter iter = iterHolder.get();
+            if (iter == null) {
+                iter = new Iter(it, this.world);
+                iterHolder.set(iter);
             } else {
-                iterHolder[0].setNativeIter(it);
+                iter.setNativeIter(it);
             }
-            callback.accept(iterHolder[0]);
+            callback.accept(iter);
         }, this.world.arena());
 
         ecs_system_desc_t.run(this.desc, callbackStub);