fix: properly implement memory barriers

game/core/src/main/de/dhbw/tinf22b6/gameobject/GameObject.java

@@ -41,6 +41,14 @@ public Body getBody() {
         return body;
     }
 
+    public void setBody(Body body) {
+        this.body = body;
+    }
+
+    public short getCollisionMask() {
+        return collisionMask;
+    }
+
     public boolean isRemove() {
         return remove;
     }

game/core/src/main/de/dhbw/tinf22b6/gameobject/bullet/Bullet.java

@@ -10,6 +10,7 @@
 import com.badlogic.gdx.physics.box2d.World;
 import de.dhbw.tinf22b6.gameobject.GameObject;
 import de.dhbw.tinf22b6.util.Constants;
+import de.dhbw.tinf22b6.util.EntitySystem;
 import de.dhbw.tinf22b6.world.Box2dWorld;
 import de.dhbw.tinf22b6.world.WorldParser;
 
@@ -19,8 +20,6 @@ public abstract class Bullet extends GameObject {
     protected boolean active;
     protected float angle;
     protected float r;
-    // shitty mutex implementation
-    private static boolean canCreateBullet = true;
     // be careful when adjusting this parameter, as this is not the range in tiles but rather a
     // counting of delta times
     // speed until the "range" is reached
@@ -35,37 +34,7 @@ public Bullet(String region, Vector2 position, float angle, int damage, short ma
         speed = 3;
         width = 3;
         height = 6;
-        // This is arcane wizardry! It might fix the crash which happened at random when
-        // the player gets into the range of multiple enemies at the same time, and they start shooting
-        // in the same tick - effectively locking up the world (inserting body) and causing a data race
-        // this "fix" works for me and needs throughout testing as I suspect it breaking something further
-        // when the #render() call is done and the body is not created yet.
-        new Thread(() -> {
-                    World world = Box2dWorld.instance.getWorld();
-                    boolean isLocked;
-                    do {
-                        isLocked = world.isLocked();
-                    } while (isLocked);
-                    boolean canCreate;
-                    do {
-                        canCreate = canCreateBullet;
-                    } while (!canCreate);
-                    canCreateBullet = false;
-                    body = world.createBody(WorldParser.getDynamicBodyDef(pos.x + width / 2, pos.y + height / 2));
-                    PolygonShape polygonShape = new PolygonShape();
-                    polygonShape.setAsBox(3 - 2, 3 - 2);
-
-                    FixtureDef fixtureDef = new FixtureDef();
-                    fixtureDef.shape = polygonShape;
-                    fixtureDef.filter.categoryBits = collisionMask;
-                    fixtureDef.isSensor = true;
-
-                    body.createFixture(fixtureDef).setUserData(this);
-                    body.setBullet(true);
-                    polygonShape.dispose();
-                    canCreateBullet = true;
-                })
-                .start();
+        EntitySystem.instance.addBulletToQueue(this);
     }
 
     @Override

game/core/src/main/de/dhbw/tinf22b6/gameobject/enemy/Enemy.java

@@ -384,26 +384,12 @@ public Vector2 angleToVector(Vector2 outVector, float angle) {
         return SteeringUtils.angleToVector(outVector, angle);
     }
 
-    /**
-     * Overwrites the base call by spawning an AmmoBox at the target
-     * location where the Enemy died. Also, I wanted to try out
-     * Java 8s new CompletableFuture feature.
-     *
-     * @param remove specifies whether this Enemy shall be removed
-     */
     @Override
     public void setRemove(boolean remove) {
         Vector2 position = new Vector2(body.getPosition());
         position.x /= TILE_SIZE;
         position.y /= TILE_SIZE;
-        CompletableFuture.supplyAsync(() -> {
-            boolean locked;
-            do {
-                locked = Box2dWorld.instance.getWorld().isLocked();
-            } while (locked);
-            EntitySystem.instance.add(new AmmoBox(position, new Rectangle(3, 2, 10, 10)));
-            return true; // we have return something
-        });
+        EntitySystem.instance.addAmmoBoxToQueue(position);
         super.setRemove(remove);
     }
 }

game/core/src/main/de/dhbw/tinf22b6/util/EntitySystem.java

@@ -1,34 +1,53 @@
 package de.dhbw.tinf22b6.util;
 
 import com.badlogic.gdx.Gdx;
-import com.badlogic.gdx.math.Rectangle;
 import com.badlogic.gdx.math.Vector2;
 import de.dhbw.tinf22b6.gameobject.GameObject;
 import de.dhbw.tinf22b6.gameobject.Player;
+import de.dhbw.tinf22b6.gameobject.bullet.Bullet;
+
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 public class EntitySystem {
-    public enum EntityType {
-        AMMO
-    }
-
     public static final String TAG = EntitySystem.class.getName();
     public static final EntitySystem instance = new EntitySystem();
     private List<GameObject> gameObjects;
+    private List<Bullet> syncBulletsToBeCreated;
+    private List<Vector2> syncAmmoBoxesToBeCreated;
 
     // singleton: prevent instantiation from other classes
     private EntitySystem() {}
 
     public void init(List<GameObject> objectList) {
         this.gameObjects = objectList;
+        this.syncBulletsToBeCreated = Collections.synchronizedList(new ArrayList<>());
+        this.syncAmmoBoxesToBeCreated = Collections.synchronizedList(new ArrayList<>());
         Gdx.app.debug(TAG, "initialized with size: " + gameObjects.size());
     }
 
     public List<GameObject> getGameObjects() {
         return new ArrayList<>(gameObjects);
     }
 
+    public List<Vector2> getSyncAmmoBoxesToBeCreated() {
+        return syncAmmoBoxesToBeCreated;
+    }
+
+    public void addAmmoBoxToQueue(Vector2 ammoBox) {
+        this.syncAmmoBoxesToBeCreated.add(ammoBox);
+    }
+
+    public void addBulletToQueue(Bullet bullet) {
+        syncBulletsToBeCreated.add(bullet);
+    }
+
+    public List<Bullet> getSyncBulletsToBeCreated() {
+        return syncBulletsToBeCreated;
+    }
+
+
     public void add(GameObject object) {
         this.gameObjects.add(object);
     }
@@ -43,8 +62,4 @@ public Player getPlayer() {
         }
         return null;
     }
-
-    public void spawn(EntityType entityType, Vector2 pos, Rectangle rectangle) {
-        Thread thread = new Thread(() -> {});
-    }
 }

game/core/src/main/de/dhbw/tinf22b6/world/WorldController.java

@@ -3,15 +3,22 @@
 import com.badlogic.gdx.*;
 import com.badlogic.gdx.graphics.Camera;
 import com.badlogic.gdx.graphics.Cursor;
+import com.badlogic.gdx.math.Rectangle;
+import com.badlogic.gdx.math.Vector2;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
+import com.badlogic.gdx.physics.box2d.PolygonShape;
 import com.badlogic.gdx.physics.box2d.World;
 import de.dhbw.tinf22b6.gameobject.GameObject;
 import de.dhbw.tinf22b6.gameobject.Player;
+import de.dhbw.tinf22b6.gameobject.bullet.Bullet;
+import de.dhbw.tinf22b6.gameobject.interaction.AmmoBox;
 import de.dhbw.tinf22b6.screen.GameScreen;
 import de.dhbw.tinf22b6.util.CameraHelper;
 import de.dhbw.tinf22b6.util.EntitySystem;
 import de.dhbw.tinf22b6.util.PlayerStatistics;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.List;
 
 public class WorldController extends InputAdapter {
     private static final String TAG = WorldController.class.getName();
@@ -89,6 +96,39 @@ public void update(float deltaTime) {
         player.getMotionVector().x = motionX;
         player.getMotionVector().y = motionY;
 
+        List<Bullet> bullets = EntitySystem.instance.getSyncBulletsToBeCreated();
+
+        synchronized (bullets) {
+            bullets.forEach(bullet -> {
+                float width = 3;
+                float height = 6;
+                bullet.setBody(
+                        world.createBody(
+                                WorldParser.getDynamicBodyDef(
+                                        bullet.getPos().x + width / 2,
+                                        bullet.getPos().y + height / 2)));
+                PolygonShape polygonShape = new PolygonShape();
+                polygonShape.setAsBox(3 - 2, 3 - 2);
+
+                FixtureDef fixtureDef = new FixtureDef();
+                fixtureDef.shape = polygonShape;
+                fixtureDef.filter.categoryBits = bullet.getCollisionMask();
+                fixtureDef.isSensor = true;
+
+                bullet.getBody().createFixture(fixtureDef).setUserData(bullet);
+                bullet.getBody().setBullet(true);
+                polygonShape.dispose();
+            });
+            bullets.clear();
+        }
+
+        List<Vector2> ammoBoxPosition = EntitySystem.instance.getSyncAmmoBoxesToBeCreated();
+
+        synchronized (ammoBoxPosition) {
+            ammoBoxPosition.forEach(ammoBox -> EntitySystem.instance.add(new AmmoBox(ammoBox, new Rectangle(3, 2, 10, 10))));
+            ammoBoxPosition.clear();
+        }
+
         world.step(deltaTime, 6, 2);
 
         // tick objects