Weaving threads

- Restore WaitGroup abstraction
- Simplify WaitGroup to make proper use of atomics
- Fix logic error in ParallelTaskExecutor causing task counter to go
  below zero when executing main thread tasks
- Use ConcurrentHashMap in models to allow parallel access
- Reduce chunk size in RunOnAllPlan
- Only queue in InstanceManager
- Defer syncPoint within renderStage
- AbstractStorage return immutable view for tickable/dynamic instances
- Process InstanceManager queues off-thread

src/main/java/com/jozufozu/flywheel/api/task/Plan.java

@@ -1,6 +1,7 @@
 package com.jozufozu.flywheel.api.task;
 
 import com.jozufozu.flywheel.lib.task.BarrierPlan;
+import com.jozufozu.flywheel.lib.task.NestedPlan;
 
 public interface Plan {
 	/**
@@ -22,13 +23,23 @@ public interface Plan {
 	 * Create a new plan that executes this plan, then the given plan.
 	 *
 	 * @param plan The plan to execute after this plan.
-	 * @return The new, composed plan.
+	 * @return The composed plan.
 	 */
 	default Plan then(Plan plan) {
 		// TODO: AbstractPlan?
 		return new BarrierPlan(this, plan);
 	}
 
+	/**
+	 * Create a new plan that executes this plan and the given plan in parallel.
+	 *
+	 * @param plan The plan to execute in parallel with this plan.
+	 * @return The composed plan.
+	 */
+	default Plan and(Plan plan) {
+		return NestedPlan.of(this, plan);
+	}
+
 	/**
 	 * If possible, create a new plan that accomplishes everything
 	 * this plan does but with a simpler execution schedule.

src/main/java/com/jozufozu/flywheel/backend/engine/batching/BatchingDrawTracker.java

@@ -81,4 +81,9 @@ public class BatchingDrawTracker {
 			buffers.clear();
 		}
 	}
+
+	public boolean hasStage(RenderStage stage) {
+		return !activeBuffers.get(stage)
+				.isEmpty();
+	}
 }

src/main/java/com/jozufozu/flywheel/backend/engine/batching/BatchingEngine.java

@@ -82,6 +82,10 @@ public class BatchingEngine implements Engine {
 
 	@Override
 	public void renderStage(TaskExecutor executor, RenderContext context, RenderStage stage) {
+		if (!drawTracker.hasStage(stage)) {
+			return;
+		}
+		executor.syncPoint();
 		drawTracker.draw(stage);
 	}
 

src/main/java/com/jozufozu/flywheel/backend/engine/indirect/IndirectCullingGroup.java

@@ -185,4 +185,7 @@ public class IndirectCullingGroup<P extends InstancePart> {
 		meshPool.delete();
 	}
 
+	public boolean hasStage(RenderStage stage) {
+		return drawSet.contains(stage);
+	}
 }

src/main/java/com/jozufozu/flywheel/backend/engine/indirect/IndirectDrawManager.java

@@ -73,6 +73,15 @@ public class IndirectDrawManager {
 		initializedInstancers.add(instancer);
 	}
 
+	public boolean hasStage(RenderStage stage) {
+		for (var list : renderLists.values()) {
+			if (list.hasStage(stage)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	private record UninitializedInstancer(IndirectInstancer<?> instancer, Model model, RenderStage stage) {
 	}
 }

src/main/java/com/jozufozu/flywheel/backend/engine/indirect/IndirectEngine.java

@@ -53,6 +53,12 @@ public class IndirectEngine implements Engine {
 
 	@Override
 	public void renderStage(TaskExecutor executor, RenderContext context, RenderStage stage) {
+		if (!drawManager.hasStage(stage)) {
+			return;
+		}
+
+		executor.syncPoint();
+
 		try (var restoreState = GlStateTracker.getRestoreState()) {
 			setup();
 

src/main/java/com/jozufozu/flywheel/backend/engine/instancing/InstancingEngine.java

@@ -66,6 +66,8 @@ public class InstancingEngine implements Engine {
 			return;
 		}
 
+		executor.syncPoint();
+
 		try (var state = GlStateTracker.getRestoreState()) {
 			setup();
 

src/main/java/com/jozufozu/flywheel/backend/task/ParallelTaskExecutor.java

@@ -13,6 +13,7 @@ import org.slf4j.Logger;
 
 import com.jozufozu.flywheel.Flywheel;
 import com.jozufozu.flywheel.api.task.TaskExecutor;
+import com.jozufozu.flywheel.lib.task.WaitGroup;
 import com.mojang.logging.LogUtils;
 
 import net.minecraft.util.Mth;
@@ -29,17 +30,13 @@ public class ParallelTaskExecutor implements TaskExecutor {
 	 * If set to false, the executor will shut down.
 	 */
 	private final AtomicBoolean running = new AtomicBoolean(false);
-	/**
-	 * Synchronized via {@link #tasksCompletedNotifier}.
-	 */
-	private int incompleteTaskCounter = 0;
 
 	private final List<WorkerThread> threads = new ArrayList<>();
 	private final Deque<Runnable> taskQueue = new ConcurrentLinkedDeque<>();
 	private final Queue<Runnable> mainThreadQueue = new ConcurrentLinkedQueue<>();
 
 	private final Object taskNotifier = new Object();
-	private final Object tasksCompletedNotifier = new Object();
+	private final WaitGroup waitGroup = new WaitGroup();
 
 	public ParallelTaskExecutor(String name) {
 		this.name = name;
@@ -102,10 +99,6 @@ public class ParallelTaskExecutor implements TaskExecutor {
 
 		threads.clear();
 		taskQueue.clear();
-		synchronized (tasksCompletedNotifier) {
-			incompleteTaskCounter = 0;
-			tasksCompletedNotifier.notifyAll();
-		}
 	}
 
 	@Override
@@ -114,12 +107,9 @@ public class ParallelTaskExecutor implements TaskExecutor {
 			throw new IllegalStateException("Executor is stopped");
 		}
 
+		waitGroup.add();
 		taskQueue.add(task);
 
-		synchronized (tasksCompletedNotifier) {
-			incompleteTaskCounter++;
-		}
-
 		synchronized (taskNotifier) {
 			taskNotifier.notifyAll();
 		}
@@ -140,19 +130,17 @@ public class ParallelTaskExecutor implements TaskExecutor {
 	@Override
 	public void syncPoint() {
 		Runnable task;
-
 		// Finish everyone else's work...
-		while ((task = pollForSyncPoint()) != null) {
+		while (true) {
-			processTask(task);
+			if ((task = mainThreadQueue.poll()) != null) {
-		}
+				processMainThreadTask(task);
-
+			} else if ((task = taskQueue.pollLast()) != null) {
-		// and wait for any stragglers.
+				processTask(task);
-		synchronized (tasksCompletedNotifier) {
+			} else {
-			while (incompleteTaskCounter > 0) {
+				// and wait for any stragglers.
-				try {
+				waitGroup.await();
-					tasksCompletedNotifier.wait();
+				if (mainThreadQueue.isEmpty()) {
-				} catch (InterruptedException e) {
+					break;
-					//
 				}
 			}
 		}
@@ -170,23 +158,12 @@ public class ParallelTaskExecutor implements TaskExecutor {
 	public void discardAndAwait() {
 		// Discard everyone else's work...
 		while (taskQueue.pollLast() != null) {
-			synchronized (tasksCompletedNotifier) {
+			waitGroup.done();
-				if (--incompleteTaskCounter == 0) {
-					tasksCompletedNotifier.notifyAll();
-				}
-			}
 		}
 
 		// and wait for any stragglers.
-		synchronized (tasksCompletedNotifier) {
+		waitGroup.await();
-			while (incompleteTaskCounter > 0) {
+		mainThreadQueue.clear();
-				try {
-					tasksCompletedNotifier.wait();
-				} catch (InterruptedException e) {
-					//
-				}
-			}
-		}
 	}
 
 	@Nullable
@@ -213,11 +190,15 @@ public class ParallelTaskExecutor implements TaskExecutor {
 		} catch (Exception e) {
 			Flywheel.LOGGER.error("Error running task", e);
 		} finally {
-			synchronized (tasksCompletedNotifier) {
+			waitGroup.done();
-				if (--incompleteTaskCounter == 0) {
+		}
-					tasksCompletedNotifier.notifyAll();
+	}
-				}
+
-			}
+	private void processMainThreadTask(Runnable task) {
+		try {
+			task.run();
+		} catch (Exception e) {
+			Flywheel.LOGGER.error("Error running main thread task", e);
 		}
 	}
 
@@ -233,7 +214,6 @@ public class ParallelTaskExecutor implements TaskExecutor {
 	}
 
 	private class WorkerThread extends Thread {
-		private final AtomicBoolean running = ParallelTaskExecutor.this.running;
 
 		public WorkerThread(String name) {
 			super(name);
@@ -242,7 +222,7 @@ public class ParallelTaskExecutor implements TaskExecutor {
 		@Override
 		public void run() {
 			// Run until the executor shuts down
-			while (running.get()) {
+			while (ParallelTaskExecutor.this.running.get()) {
 				Runnable task = getNextTask();
 
 				if (task == null) {

src/main/java/com/jozufozu/flywheel/handler/EntityWorldHandler.java

@@ -28,7 +28,7 @@ public class EntityWorldHandler {
 
 		if (FlwUtil.canUseInstancing(level)) {
 			InstancedRenderDispatcher.getEntities(level)
-					.remove(event.getEntity());
+					.queueRemove(event.getEntity());
 		}
 	}
 }

src/main/java/com/jozufozu/flywheel/impl/instancing/InstanceWorld.java

@@ -70,11 +70,11 @@ public class InstanceWorld implements AutoCloseable {
 	 * </p>
 	 */
 	public void tick(double cameraX, double cameraY, double cameraZ) {
-		var blockEntityPlan = blockEntities.planThisTick(cameraX, cameraY, cameraZ);
+		taskExecutor.syncPoint();
-		var entityPlan = entities.planThisTick(cameraX, cameraY, cameraZ);
-		var effectPlan = effects.planThisTick(cameraX, cameraY, cameraZ);
 
-		PlanUtil.of(blockEntityPlan, entityPlan, effectPlan)
+		blockEntities.planThisTick(cameraX, cameraY, cameraZ)
+				.and(entities.planThisTick(cameraX, cameraY, cameraZ))
+				.and(effects.planThisTick(cameraX, cameraY, cameraZ))
 				.maybeSimplify()
 				.execute(taskExecutor);
 	}
@@ -114,7 +114,6 @@ public class InstanceWorld implements AutoCloseable {
 	 * Draw all instances for the given stage.
 	 */
 	public void renderStage(RenderContext context, RenderStage stage) {
-		taskExecutor.syncPoint();
 		engine.renderStage(taskExecutor, context, stage);
 	}
 

src/main/java/com/jozufozu/flywheel/impl/instancing/InstancedRenderDispatcher.java

@@ -160,7 +160,7 @@ public class InstancedRenderDispatcher {
 		// Block entities are loaded while chunks are baked.
 		// Entities are loaded with the level, so when chunks are reloaded they need to be re-added.
 		ClientLevelExtension.getAllLoadedEntities(level)
-				.forEach(world.getEntities()::add);
+				.forEach(world.getEntities()::queueAdd);
 	}
 
 	public static void addDebugInfo(List<String> info) {

src/main/java/com/jozufozu/flywheel/impl/instancing/manager/InstanceManager.java

@@ -6,7 +6,6 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 import org.joml.FrustumIntersection;
 
 import com.jozufozu.flywheel.api.instance.DynamicInstance;
-import com.jozufozu.flywheel.api.instance.Instance;
 import com.jozufozu.flywheel.api.instance.TickableInstance;
 import com.jozufozu.flywheel.api.task.Plan;
 import com.jozufozu.flywheel.config.FlwConfig;
@@ -15,7 +14,8 @@ import com.jozufozu.flywheel.impl.instancing.ratelimit.DistanceUpdateLimiter;
 import com.jozufozu.flywheel.impl.instancing.ratelimit.NonLimiter;
 import com.jozufozu.flywheel.impl.instancing.storage.Storage;
 import com.jozufozu.flywheel.impl.instancing.storage.Transaction;
-import com.jozufozu.flywheel.lib.task.PlanUtil;
+import com.jozufozu.flywheel.lib.task.RunOnAllPlan;
+import com.jozufozu.flywheel.lib.task.SimplePlan;
 
 public abstract class InstanceManager<T> {
 	private final Queue<Transaction<T>> queue = new ConcurrentLinkedQueue<>();
@@ -47,14 +47,6 @@ public abstract class InstanceManager<T> {
 		return getStorage().getAllInstances().size();
 	}
 
-	public void add(T obj) {
-		if (!getStorage().willAccept(obj)) {
-			return;
-		}
-
-		getStorage().add(obj);
-	}
-
 	public void queueAdd(T obj) {
 		if (!getStorage().willAccept(obj)) {
 			return;
@@ -63,33 +55,10 @@ public abstract class InstanceManager<T> {
 		queue.add(Transaction.add(obj));
 	}
 
-	public void remove(T obj) {
-		getStorage().remove(obj);
-	}
-
 	public void queueRemove(T obj) {
 		queue.add(Transaction.remove(obj));
 	}
 
-	/**
-	 * Update the instance associated with an object.
-	 *
-	 * <p>
-	 *     By default this is the only hook an {@link Instance} has to change its internal state. This is the lowest frequency
-	 *     update hook {@link Instance} gets. For more frequent updates, see {@link TickableInstance} and
-	 *     {@link DynamicInstance}.
-	 * </p>
-	 *
-	 * @param obj the object to update.
-	 */
-	public void update(T obj) {
-		if (!getStorage().willAccept(obj)) {
-			return;
-		}
-
-		getStorage().update(obj);
-	}
-
 	public void queueUpdate(T obj) {
 		if (!getStorage().willAccept(obj)) {
 			return;
@@ -115,9 +84,11 @@ public abstract class InstanceManager<T> {
 	}
 
 	public Plan planThisTick(double cameraX, double cameraY, double cameraZ) {
-		tickLimiter.tick();
+		return SimplePlan.of(() -> {
-		processQueue();
+					tickLimiter.tick();
-		return PlanUtil.runOnAll(getStorage()::getTickableInstances, instance -> tickInstance(instance, cameraX, cameraY, cameraZ));
+					processQueue();
+				})
+				.then(RunOnAllPlan.of(getStorage()::getTickableInstances, instance -> tickInstance(instance, cameraX, cameraY, cameraZ)));
 	}
 
 	protected void tickInstance(TickableInstance instance, double cameraX, double cameraY, double cameraZ) {
@@ -127,9 +98,11 @@ public abstract class InstanceManager<T> {
 	}
 
 	public Plan planThisFrame(double cameraX, double cameraY, double cameraZ, FrustumIntersection frustum) {
-		frameLimiter.tick();
+		return SimplePlan.of(() -> {
-		processQueue();
+					frameLimiter.tick();
-		return PlanUtil.runOnAll(getStorage()::getDynamicInstances, instance -> updateInstance(instance, cameraX, cameraY, cameraZ, frustum));
+					processQueue();
+				})
+				.then(RunOnAllPlan.of(getStorage()::getDynamicInstances, instance -> updateInstance(instance, cameraX, cameraY, cameraZ, frustum)));
 	}
 
 	protected void updateInstance(DynamicInstance instance, double cameraX, double cameraY, double cameraZ, FrustumIntersection frustum) {

src/main/java/com/jozufozu/flywheel/impl/instancing/storage/AbstractStorage.java

@@ -1,6 +1,7 @@
 package com.jozufozu.flywheel.impl.instancing.storage;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 import com.jozufozu.flywheel.api.backend.Engine;
@@ -11,7 +12,9 @@ import com.jozufozu.flywheel.api.instance.TickableInstance;
 public abstract class AbstractStorage<T> implements Storage<T> {
 	protected final Engine engine;
 	protected final List<TickableInstance> tickableInstances = new ArrayList<>();
+	protected final List<TickableInstance> tickableInstancesView = Collections.unmodifiableList(tickableInstances);
 	protected final List<DynamicInstance> dynamicInstances = new ArrayList<>();
+	protected final List<DynamicInstance> dynamicInstancesView = Collections.unmodifiableList(dynamicInstances);
 
 	protected AbstractStorage(Engine engine) {
 		this.engine = engine;
@@ -19,12 +22,12 @@ public abstract class AbstractStorage<T> implements Storage<T> {
 
 	@Override
 	public List<TickableInstance> getTickableInstances() {
-		return tickableInstances;
+		return tickableInstancesView;
 	}
 
 	@Override
 	public List<DynamicInstance> getDynamicInstances() {
-		return dynamicInstances;
+		return dynamicInstancesView;
 	}
 
 	protected void setup(Instance instance) {

src/main/java/com/jozufozu/flywheel/lib/light/LightUpdater.java

@@ -1,6 +1,8 @@
 package com.jozufozu.flywheel.lib.light;
 
+import java.util.Queue;
 import java.util.Set;
+import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.stream.Stream;
 
 import com.jozufozu.flywheel.lib.box.ImmutableBox;
@@ -26,6 +28,8 @@ public class LightUpdater {
 	private final WeakContainmentMultiMap<LightListener> listenersBySection = new WeakContainmentMultiMap<>();
 	private final Set<TickingLightListener> tickingListeners = FlwUtil.createWeakHashSet();
 
+	private final Queue<LightListener> queue = new ConcurrentLinkedQueue<>();
+
 	public static LightUpdater get(LevelAccessor level) {
 		if (LightUpdated.receivesLightUpdates(level)) {
 			// The level is valid, add it to the map.
@@ -41,8 +45,8 @@ public class LightUpdater {
 	}
 
 	public void tick() {
+		processQueue();
 		tickSerial();
-		//tickParallel();
 	}
 
 	private void tickSerial() {
@@ -59,8 +63,20 @@ public class LightUpdater {
 	 * @param listener The object that wants to receive light update notifications.
 	 */
 	public void addListener(LightListener listener) {
-		if (listener instanceof TickingLightListener)
+		queue.add(listener);
+	}
+
+	private synchronized void processQueue() {
+		LightListener listener;
+		while ((listener = queue.poll()) != null) {
+			doAdd(listener);
+		}
+	}
+
+	private void doAdd(LightListener listener) {
+		if (listener instanceof TickingLightListener) {
 			tickingListeners.add(((TickingLightListener) listener));
+		}
 
 		ImmutableBox box = listener.getVolume();
 
@@ -94,9 +110,13 @@ public class LightUpdater {
 	 * @param pos  The section position where light changed.
 	 */
 	public void onLightUpdate(LightLayer type, SectionPos pos) {
+		processQueue();
+
 		Set<LightListener> listeners = listenersBySection.get(pos.asLong());
 
-		if (listeners == null || listeners.isEmpty()) return;
+		if (listeners == null || listeners.isEmpty()) {
+			return;
+		}
 
 		listeners.removeIf(LightListener::isInvalid);
 

src/main/java/com/jozufozu/flywheel/lib/model/Models.java

@@ -1,8 +1,8 @@
 package com.jozufozu.flywheel.lib.model;
 
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import com.jozufozu.flywheel.api.event.ReloadRenderersEvent;
 import com.jozufozu.flywheel.api.model.Model;
@@ -16,9 +16,9 @@ import net.minecraft.core.Direction;
 import net.minecraft.world.level.block.state.BlockState;
 
 public final class Models {
-	private static final Map<BlockState, Model> BLOCK_STATE = new HashMap<>();
+	private static final Map<BlockState, Model> BLOCK_STATE = new ConcurrentHashMap<>();
-	private static final Map<PartialModel, Model> PARTIAL = new HashMap<>();
+	private static final Map<PartialModel, Model> PARTIAL = new ConcurrentHashMap<>();
-	private static final Map<Pair<PartialModel, Direction>, Model> PARTIAL_DIR = new HashMap<>();
+	private static final Map<Pair<PartialModel, Direction>, Model> PARTIAL_DIR = new ConcurrentHashMap<>();
 
 	public static Model block(BlockState state) {
 		return BLOCK_STATE.computeIfAbsent(state, it -> new BlockModelBuilder(it).build());

src/main/java/com/jozufozu/flywheel/lib/task/NestedPlan.java

@@ -4,12 +4,13 @@ import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.List;
 
+import com.google.common.collect.ImmutableList;
 import com.jozufozu.flywheel.api.task.Plan;
 import com.jozufozu.flywheel.api.task.TaskExecutor;
 
 public record NestedPlan(List<Plan> parallelPlans) implements Plan {
 	public static NestedPlan of(Plan... plans) {
-		return new NestedPlan(List.of(plans));
+		return new NestedPlan(ImmutableList.copyOf(plans));
 	}
 
 	@Override
@@ -33,6 +34,14 @@ public record NestedPlan(List<Plan> parallelPlans) implements Plan {
 		}
 	}
 
+	@Override
+	public Plan and(Plan plan) {
+		return new NestedPlan(ImmutableList.<Plan>builder()
+				.addAll(parallelPlans)
+				.add(plan)
+				.build());
+	}
+
 	@Override
 	public Plan maybeSimplify() {
 		if (parallelPlans.isEmpty()) {

src/main/java/com/jozufozu/flywheel/lib/task/PlanUtil.java

@@ -1,15 +1,10 @@
 package com.jozufozu.flywheel.lib.task;
 
 import java.util.List;
-import java.util.function.Consumer;
-import java.util.function.Supplier;
 
 import com.jozufozu.flywheel.api.task.Plan;
 
 public class PlanUtil {
-	public static <T> Plan runOnAll(Supplier<List<T>> iterable, Consumer<T> forEach) {
-		return new RunOnAllPlan<>(iterable, forEach);
-	}
 
 	public static Plan of() {
 		return UnitPlan.INSTANCE;

src/main/java/com/jozufozu/flywheel/lib/task/RunOnAllPlan.java

@@ -8,16 +8,19 @@ import com.jozufozu.flywheel.api.task.Plan;
 import com.jozufozu.flywheel.api.task.TaskExecutor;
 
 public record RunOnAllPlan<T>(Supplier<List<T>> listSupplier, Consumer<T> action) implements Plan {
+	public static <T> Plan of(Supplier<List<T>> iterable, Consumer<T> forEach) {
+		return new RunOnAllPlan<>(iterable, forEach);
+	}
+
 	@Override
 	public void execute(TaskExecutor taskExecutor, Runnable onCompletion) {
-		// TODO: unit tests, fix CME?
 		taskExecutor.execute(() -> {
 			var list = listSupplier.get();
 			final int size = list.size();
 
 			if (size == 0) {
 				onCompletion.run();
-			} else if (size <= getChunkingThreshold(taskExecutor)) {
+			} else if (size <= getChunkingThreshold()) {
 				processList(list, onCompletion);
 			} else {
 				dispatchChunks(list, taskExecutor, onCompletion);
@@ -27,12 +30,9 @@ public record RunOnAllPlan<T>(Supplier<List<T>> listSupplier, Consumer<T> action
 
 	private void dispatchChunks(List<T> suppliedList, TaskExecutor taskExecutor, Runnable onCompletion) {
 		final int size = suppliedList.size();
-		final int threadCount = taskExecutor.getThreadCount();
+		final int chunkSize = getChunkSize(taskExecutor, size);
 
-		final int chunkSize = (size + threadCount - 1) / threadCount; // ceiling division
+		var synchronizer = new Synchronizer(ceilingDiv(size, chunkSize), onCompletion);
-		final int chunkCount = (size + chunkSize - 1) / chunkSize; // ceiling division
-
-		var synchronizer = new Synchronizer(chunkCount, onCompletion);
 		int remaining = size;
 
 		while (remaining > 0) {
@@ -45,6 +45,14 @@ public record RunOnAllPlan<T>(Supplier<List<T>> listSupplier, Consumer<T> action
 		}
 	}
 
+	private static int getChunkSize(TaskExecutor taskExecutor, int totalSize) {
+		return ceilingDiv(totalSize, taskExecutor.getThreadCount() * 32);
+	}
+
+	private static int ceilingDiv(int numerator, int denominator) {
+		return (numerator + denominator - 1) / denominator;
+	}
+
 	private void processList(List<T> suppliedList, Runnable onCompletion) {
 		for (T t : suppliedList) {
 			action.accept(t);
@@ -52,7 +60,7 @@ public record RunOnAllPlan<T>(Supplier<List<T>> listSupplier, Consumer<T> action
 		onCompletion.run();
 	}
 
-	private static int getChunkingThreshold(TaskExecutor taskExecutor) {
+	private static int getChunkingThreshold() {
-		return 512;
+		return 256;
 	}
 }

src/main/java/com/jozufozu/flywheel/lib/task/SimplePlan.java

@@ -18,7 +18,7 @@ public record SimplePlan(List<Runnable> parallelTasks) implements Plan {
 		}
 
 		var synchronizer = new Synchronizer(parallelTasks.size(), onCompletion);
-		for (Runnable task : parallelTasks) {
+		for (var task : parallelTasks) {
 			taskExecutor.execute(() -> {
 				task.run();
 				synchronizer.decrementAndEventuallyRun();

src/main/java/com/jozufozu/flywheel/lib/task/WaitGroup.java

@@ -0,0 +1,59 @@
+package com.jozufozu.flywheel.lib.task;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+// https://stackoverflow.com/questions/29655531
+public class WaitGroup {
+	private final AtomicInteger counter = new AtomicInteger(0);
+
+	public void add() {
+		add(1);
+	}
+
+	public void add(int i) {
+		if (i == 0) {
+			return;
+		}
+
+		counter.addAndGet(i);
+	}
+
+	public void done() {
+		var result = counter.decrementAndGet();
+		if (result == 0) {
+			synchronized (this) {
+				this.notifyAll();
+			}
+		} else if (result < 0) {
+			throw new IllegalStateException("WaitGroup counter is negative!");
+		}
+	}
+
+	public void await() {
+		try {
+			awaitInternal();
+		} catch (InterruptedException ignored) {
+			// noop
+		}
+	}
+
+	private void awaitInternal() throws InterruptedException {
+		//		var start = System.nanoTime();
+		while (counter.get() > 0) {
+			// spin in place to avoid sleeping the main thread
+			//			synchronized (this) {
+			//				this.wait(timeoutMs);
+			//			}
+		}
+		//		var end = System.nanoTime();
+		//		var elapsed = end - start;
+		//
+		//		if (elapsed > 1000000) {
+		//			Flywheel.LOGGER.info("Waited " + StringUtil.formatTime(elapsed));
+		//		}
+	}
+
+	public void _reset() {
+		counter.set(0);
+	}
+}

src/main/java/com/jozufozu/flywheel/mixin/instancemanage/InstanceAddMixin.java

@@ -25,7 +25,7 @@ public class InstanceAddMixin {
 	private void flywheel$onBlockEntityAdded(BlockEntity blockEntity, CallbackInfo ci) {
 		if (level.isClientSide && FlwUtil.canUseInstancing(level)) {
 			InstancedRenderDispatcher.getBlockEntities(level)
-					.add(blockEntity);
+					.queueAdd(blockEntity);
 		}
 	}
 }

src/main/java/com/jozufozu/flywheel/mixin/instancemanage/InstanceRemoveMixin.java

@@ -24,7 +24,7 @@ public class InstanceRemoveMixin {
 	private void flywheel$removeInstance(CallbackInfo ci) {
 		if (level instanceof ClientLevel && FlwUtil.canUseInstancing(level)) {
 			InstancedRenderDispatcher.getBlockEntities(level)
-					.remove((BlockEntity) (Object) this);
+					.queueRemove((BlockEntity) (Object) this);
 		}
 	}
 

src/main/java/com/jozufozu/flywheel/mixin/instancemanage/InstanceUpdateMixin.java

@@ -35,6 +35,6 @@ public class InstanceUpdateMixin {
 		}
 
 		InstancedRenderDispatcher.getBlockEntities(level)
-				.update(blockEntity);
+				.queueUpdate(blockEntity);
 	}
 }

src/test/java/com/jozufozu/flywheel/lib/task/PlanCompositionTest.java

@@ -0,0 +1,20 @@
+package com.jozufozu.flywheel.lib.task;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import com.jozufozu.flywheel.api.task.Plan;
+
+public class PlanCompositionTest {
+
+	public static final Runnable NOOP = () -> {
+	};
+	public static final Plan SIMPLE = SimplePlan.of(NOOP);
+
+	@Test
+	void nestedPlanAnd() {
+		var empty = NestedPlan.of(SIMPLE);
+
+		Assertions.assertEquals(NestedPlan.of(SIMPLE, SIMPLE), empty.and(SIMPLE));
+	}
+}

src/test/java/com/jozufozu/flywheel/lib/task/WaitGroupTest.java

@@ -0,0 +1,14 @@
+package com.jozufozu.flywheel.lib.task;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class WaitGroupTest {
+	@Test
+	public void testExtraDone() {
+		WaitGroup wg = new WaitGroup();
+		wg.add();
+		wg.done();
+		Assertions.assertThrows(IllegalStateException.class, wg::done);
+	}
+}