Unionized threads

- Allow the user to configure the number of worker threads
- Allow the user to disable parallelism entirely without a jvm flag
- Move thread count logic into FlwTaskExecutor and make
  ParallelTaskExecutor simply take a thread count as a parameter

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

@@ -66,5 +66,5 @@ public interface TaskExecutor extends Executor {
 	 *
 	 * @return The number of threads this executor uses.
 	 */
-	int getThreadCount();
+	int threadCount();
 }

src/main/java/com/jozufozu/flywheel/config/FlwConfig.java

@@ -66,6 +66,10 @@ public class FlwConfig {
 		return client.limitUpdates.get();
 	}
 
+	public int workerThreads() {
+		return client.workerThreads.get();
+	}
+
 	public void registerSpecs(ModLoadingContext context) {
 		context.registerConfig(ModConfig.Type.CLIENT, clientSpec);
 	}
@@ -73,6 +77,7 @@ public class FlwConfig {
 	public static class ClientConfig {
 		public final ConfigValue<String> backend;
 		public final BooleanValue limitUpdates;
+		public final ForgeConfigSpec.IntValue workerThreads;
 
 		private ClientConfig(ForgeConfigSpec.Builder builder) {
 			backend = builder.comment("Select the backend to use.")
@@ -80,6 +85,10 @@ public class FlwConfig {
 
 			limitUpdates = builder.comment("Enable or disable instance update limiting with distance.")
 					.define("limitUpdates", true);
+
+			workerThreads = builder.comment("The number of worker threads to use. Set to -1 to let Flywheel decide. Set to 0 to disable parallelism. Requires a game restart to take effect.")
+					.defineInRange("workerThreads", -1, -1, Runtime.getRuntime()
+							.availableProcessors());
 		}
 	}
 }

src/main/java/com/jozufozu/flywheel/impl/task/FlwTaskExecutor.java

@@ -4,11 +4,12 @@ import org.apache.commons.lang3.concurrent.AtomicSafeInitializer;
 import org.apache.commons.lang3.concurrent.ConcurrentUtils;
 
 import com.jozufozu.flywheel.api.task.TaskExecutor;
+import com.jozufozu.flywheel.config.FlwConfig;
 import com.mojang.blaze3d.systems.RenderSystem;
 
-public final class FlwTaskExecutor {
-	public static final boolean USE_SERIAL_EXECUTOR = System.getProperty("flw.useSerialExecutor") != null;
+import net.minecraft.util.Mth;
 
+public final class FlwTaskExecutor {
 	private static final Initializer INITIALIZER = new Initializer();
 
 	private FlwTaskExecutor() {
@@ -22,14 +23,34 @@ public final class FlwTaskExecutor {
 		return ConcurrentUtils.initializeUnchecked(INITIALIZER);
 	}
 
+	/**
+	 * Returns the "optimal" number of threads to be used for tasks. This will always return at least one thread.
+	 */
+	private static int getOptimalThreadCount() {
+		return Mth.clamp(Math.max(getMaxThreadCount() / 3, getMaxThreadCount() - 6), 1, 10);
+	}
+
+	private static int getMaxThreadCount() {
+		return Runtime.getRuntime()
+				.availableProcessors();
+	}
+
+
 	private static class Initializer extends AtomicSafeInitializer<TaskExecutor> {
 		@Override
 		protected TaskExecutor initialize() {
-			if (USE_SERIAL_EXECUTOR) {
+			int threadCount = FlwConfig.get()
+					.workerThreads();
+
+			if (threadCount == 0) {
 				return SerialTaskExecutor.INSTANCE;
+			} else if (threadCount < 0) {
+				threadCount = getOptimalThreadCount();
+			} else {
+				threadCount = Mth.clamp(threadCount, 1, getMaxThreadCount());
 			}
 
-			ParallelTaskExecutor executor = new ParallelTaskExecutor("Flywheel", RenderSystem::isOnRenderThread);
+			ParallelTaskExecutor executor = new ParallelTaskExecutor("Flywheel", threadCount, RenderSystem::isOnRenderThread);
 			executor.startWorkers();
 			return executor;
 		}

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

@@ -38,14 +38,14 @@ public class ParallelTaskExecutor implements TaskExecutor {
 	private final ThreadGroupNotifier taskNotifier = new ThreadGroupNotifier();
 	private final WaitGroup waitGroup = new WaitGroup();
 
-	public ParallelTaskExecutor(String name, BooleanSupplier mainThreadQuery) {
+	public ParallelTaskExecutor(String name, int threadCount, BooleanSupplier mainThreadQuery) {
 		this.name = name;
 		this.mainThreadQuery = mainThreadQuery;
-		threadCount = getOptimalThreadCount();
+		this.threadCount = threadCount;
 	}
 
 	@Override
-	public int getThreadCount() {
+	public int threadCount() {
 		return threadCount;
 	}
 
@@ -247,17 +247,6 @@ public class ParallelTaskExecutor implements TaskExecutor {
 		}
 	}
 
-	/**
-	 * Returns the "optimal" number of threads to be used for tasks. This will always return at least one thread.
-	 */
-	private static int getOptimalThreadCount() {
-		return Mth.clamp(Math.max(getMaxThreadCount() / 3, getMaxThreadCount() - 6), 1, 10);
-	}
-
-	private static int getMaxThreadCount() {
-		return Runtime.getRuntime().availableProcessors();
-	}
-
 	private class WorkerThread extends Thread {
 		public WorkerThread(String name) {
 			super(name);

src/main/java/com/jozufozu/flywheel/impl/task/SerialTaskExecutor.java

@@ -35,7 +35,7 @@ public class SerialTaskExecutor implements TaskExecutor {
 	}
 
 	@Override
-	public int getThreadCount() {
+	public int threadCount() {
 		return 1;
 	}
 

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

@@ -182,7 +182,7 @@ public final class Distribute {
 	}
 
 	public static int sliceSize(TaskExecutor taskExecutor, int totalSize, int denominator) {
-		return MoreMath.ceilingDiv(totalSize, taskExecutor.getThreadCount() * denominator);
+		return MoreMath.ceilingDiv(totalSize, taskExecutor.threadCount() * denominator);
 	}
 
 	private Distribute() {

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

@@ -27,7 +27,7 @@ class PlanExecutionTest {
 	@BeforeEach
 	public void setUp() {
 		var currentThread = Thread.currentThread();
-		EXECUTOR = new ParallelTaskExecutor("PlanTest", () -> currentThread == Thread.currentThread());
+		EXECUTOR = new ParallelTaskExecutor("PlanTest", 2, () -> currentThread == Thread.currentThread());
 		EXECUTOR.startWorkers();
 	}