feat: fix ExecutorCompletionService workaround in ChunkProcessingPipe…

…line (MovingBlocks#5128)

engine/src/main/java/org/terasology/engine/world/chunks/pipeline/ChunkExecutorCompletionService.java

@@ -0,0 +1,126 @@
+// Copyright 2023 The Terasology Foundation
+// SPDX-License-Identifier: Apache-2.0
+
+package org.terasology.engine.world.chunks.pipeline;
+
+import org.joml.Vector3i;
+import org.joml.Vector3ic;
+import org.terasology.engine.world.chunks.Chunk;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CompletionService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A specialised alternative to {@link java.util.concurrent.ExecutorCompletionService},
+ * used for submitting chunk tasks and queuing their results.
+ *
+ * Whilst this class adheres to the {@link CompletionService} interface, use of the class's
+ * {@link #submit(Callable, Vector3ic)} overload is preferred over those inherited from the interface.
+ */
+public class ChunkExecutorCompletionService implements CompletionService<Chunk> {
+    private static final Vector3ic EMPTY_VECTOR3I = new Vector3i();
+    private final ThreadPoolExecutor threadPoolExecutor;
+    private final BlockingQueue<Future<Chunk>> completionQueue;
+
+    private final class ChunkFutureWithCompletion extends PositionFuture<Chunk> {
+        ChunkFutureWithCompletion(Callable callable, Vector3ic position) {
+            super(callable, position);
+        }
+
+        ChunkFutureWithCompletion(Runnable runnable, Chunk result, Vector3ic position) {
+            super(runnable, result, position);
+        }
+
+        @Override
+        protected void done() {
+            super.done();
+            try {
+                completionQueue.put(this);
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
+    public ChunkExecutorCompletionService(ThreadPoolExecutor threadPoolExecutor, BlockingQueue<Future<Chunk>> completionQueue) {
+        this.threadPoolExecutor = threadPoolExecutor;
+        this.completionQueue = completionQueue;
+    }
+
+    /**
+     * Submits a task to be executed.
+     * @param callable the task to submit
+     *
+     * @deprecated Use {@link #submit(Callable, Vector3ic)} instead
+     */
+    @Override
+    @Deprecated
+    public Future<Chunk> submit(Callable<Chunk> callable) {
+        RunnableFuture<Chunk> task = new ChunkFutureWithCompletion(callable, EMPTY_VECTOR3I);
+        threadPoolExecutor.execute(task);
+        return task;
+    }
+
+    /**
+     * Submits a chunk task to be executed.
+     * @param callable the chunk task to execute.
+     * @param position the position of the chunk.
+     * @return the submitted task.
+     */
+    public Future<Chunk> submit(Callable<Chunk> callable, Vector3ic position) {
+        RunnableFuture<Chunk> task = new ChunkFutureWithCompletion(callable, position);
+        threadPoolExecutor.execute(task);
+        return task;
+    }
+
+    /**
+     * Submits a task to be executed.
+     * @param runnable the task to run.
+     * @param value the value to return upon task completion.
+     *
+     * @deprecated Use {@link #submit(Callable, Vector3ic)} instead
+     */
+    @Override
+    @Deprecated
+    public Future<Chunk> submit(Runnable runnable, Chunk value) {
+        RunnableFuture<Chunk> task = new ChunkFutureWithCompletion(runnable, value, EMPTY_VECTOR3I);
+        threadPoolExecutor.execute(task);
+        return task;
+    }
+
+    /**
+     * Retrieves a completed task from the queue.
+     * @return a completed task.
+     * @throws InterruptedException if interrupted whilst waiting on the queue.
+     */
+    @Override
+    public Future<Chunk> take() throws InterruptedException {
+        return completionQueue.take();
+    }
+
+    /**
+     * Retrieves a completed task from the queue if not empty.
+     * @return a completed task, or null if there are no tasks in the queue.
+     */
+    @Override
+    public Future<Chunk> poll() {
+        return completionQueue.poll();
+    }
+
+    /**
+     * Retrieves a completed task from the queue if not empty.
+     * @param l the timeout duration before returning null.
+     * @param timeUnit the time units of the timeout duration.
+     *
+     * @return a completed task, or null if there are no tasks in the queue.
+     */
+    @Override
+    public Future<Chunk> poll(long l, TimeUnit timeUnit) throws InterruptedException {
+        return completionQueue.poll(l, timeUnit);
+    }
+}

engine/src/main/java/org/terasology/engine/world/chunks/pipeline/ChunkProcessingPipeline.java

@@ -13,22 +13,17 @@
 import org.slf4j.LoggerFactory;
 import org.terasology.engine.monitoring.ThreadActivity;
 import org.terasology.engine.monitoring.ThreadMonitor;
-import org.terasology.engine.utilities.ReflectionUtil;
 import org.terasology.engine.world.chunks.Chunk;
 import org.terasology.engine.world.chunks.pipeline.stages.ChunkTask;
 import org.terasology.engine.world.chunks.pipeline.stages.ChunkTaskProvider;
 
 import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.Callable;
 import java.util.concurrent.CancellationException;
-import java.util.concurrent.CompletionService;
 import java.util.concurrent.ExecutionException;
-import java.util.concurrent.ExecutorCompletionService;
 import java.util.concurrent.Future;
 import java.util.concurrent.PriorityBlockingQueue;
-import java.util.concurrent.RunnableFuture;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
@@ -50,7 +45,7 @@ public class ChunkProcessingPipeline {
 
     private final List<ChunkTaskProvider> stages = Lists.newArrayList();
     private final Thread reactor;
-    private final CompletionService<Chunk> chunkProcessor;
+    private final ChunkExecutorCompletionService chunkProcessor;
     private final ThreadPoolExecutor executor;
     private final Function<Vector3ic, Chunk> chunkProvider;
     private final Map<Vector3ic, ChunkProcessingInfo> chunkProcessingInfoMap = Maps.newConcurrentMap();
@@ -66,36 +61,18 @@ public ChunkProcessingPipeline(Function<Vector3ic, Chunk> chunkProvider, Compara
                 NUM_TASK_THREADS,
                 NUM_TASK_THREADS, 0L,
                 TimeUnit.MILLISECONDS,
-                new PriorityBlockingQueue(800, unwrappingComporator(comparable)),
+                new PriorityBlockingQueue(800, comparable),
                 this::threadFactory,
-                this::rejectQueueHandler) {
-            @Override
-            protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
-                RunnableFuture<T> newTaskFor = super.newTaskFor(callable);
-                return new PositionFuture<>(newTaskFor, ((PositionalCallable) callable).getPosition());
-            }
-        };
+                this::rejectQueueHandler);
         logger.debug("allocated {} threads", NUM_TASK_THREADS);
-        chunkProcessor = new ExecutorCompletionService<>(executor,
+        chunkProcessor = new ChunkExecutorCompletionService(executor,
                 new PriorityBlockingQueue<>(800, comparable));
         reactor = new Thread(this::chunkTaskHandler);
         reactor.setDaemon(true);
         reactor.setName("Chunk-Processing-Reactor");
         reactor.start();
     }
 
-    /**
-     * BlackMagic method: {@link ExecutorCompletionService} wraps task with QueueingFuture (private access)
-     * there takes wrapped task for comparing in {@link ThreadPoolExecutor}
-     */
-    private Comparator unwrappingComporator(Comparator<Future<Chunk>> comparable) {
-        return (o1, o2) -> {
-                Object unwrapped1 = ReflectionUtil.readField(o1, "task");
-                Object unwrapped2 = ReflectionUtil.readField(o2, "task");
-                return comparable.compare((Future<Chunk>) unwrapped1, (Future<Chunk>) unwrapped2);
-        };
-    }
-
     /**
      * Reactor thread. Handles all ChunkTask dependency logic and running.
      */
@@ -190,11 +167,11 @@ private Chunk getChunkBy(ChunkTaskProvider requiredStage, Vector3ic position) {
     }
 
     private Future<Chunk> runTask(ChunkTask task, List<Chunk> chunks) {
-        return chunkProcessor.submit(new PositionalCallable(() -> {
+        return chunkProcessor.submit(() -> {
             try (ThreadActivity ignored = ThreadMonitor.startThreadActivity(task.getName())) {
                 return task.apply(chunks);
             }
-        }, task.getPosition()));
+        }, task.getPosition());
     }
 
     private Thread threadFactory(Runnable runnable) {
@@ -236,8 +213,7 @@ public ListenableFuture<Chunk> invokeGeneratorTask(Vector3ic position, Supplier<
             SettableFuture<Chunk> exitFuture = SettableFuture.create();
             chunkProcessingInfo = new ChunkProcessingInfo(position, exitFuture);
             chunkProcessingInfoMap.put(position, chunkProcessingInfo);
-            chunkProcessingInfo.setCurrentFuture(chunkProcessor.submit(new PositionalCallable(generatorTask::get,
-                    position)));
+            chunkProcessingInfo.setCurrentFuture(chunkProcessor.submit(generatorTask::get, position));
             return exitFuture;
         }
     }
@@ -317,26 +293,4 @@ public boolean isPositionProcessing(Vector3ic pos) {
     public Iterable<Vector3ic> getProcessingPosition() {
         return chunkProcessingInfoMap.keySet();
     }
-
-    /**
-     * Dummy callable for passthru position for {@link java.util.concurrent.ThreadPoolExecutor}#newTaskFor
-     */
-    private static final class PositionalCallable implements Callable<Chunk> {
-        private final Callable<Chunk> callable;
-        private final Vector3ic position;
-
-        private PositionalCallable(Callable<Chunk> callable, Vector3ic position) {
-            this.callable = callable;
-            this.position = position;
-        }
-
-        public Vector3ic getPosition() {
-            return position;
-        }
-
-        @Override
-        public Chunk call() throws Exception {
-            return callable.call();
-        }
-    }
 }

engine/src/main/java/org/terasology/engine/world/chunks/pipeline/PositionFuture.java

@@ -5,53 +5,23 @@
 
 import org.joml.Vector3ic;
 
-import java.util.concurrent.ExecutionException;
-import java.util.concurrent.RunnableFuture;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
+import java.util.concurrent.Callable;
+import java.util.concurrent.FutureTask;
 
-public class PositionFuture<T> implements RunnableFuture<T> {
-
-    private final RunnableFuture<T> delegate;
+public class PositionFuture<T> extends FutureTask<T> {
     private final Vector3ic position;
 
-    public PositionFuture(RunnableFuture<T> delegate, Vector3ic position) {
-        this.delegate = delegate;
+    public PositionFuture(Callable callable, Vector3ic position) {
+        super(callable);
         this.position = position;
     }
 
-    public Vector3ic getPosition() {
-        return position;
-    }
-
-    @Override
-    public void run() {
-        delegate.run();
-    }
-
-    @Override
-    public boolean cancel(boolean mayInterruptIfRunning) {
-        return delegate.cancel(mayInterruptIfRunning);
-    }
-
-    @Override
-    public boolean isCancelled() {
-        return delegate.isCancelled();
-    }
-
-    @Override
-    public boolean isDone() {
-        return delegate.isDone();
-    }
-
-    @Override
-    public T get() throws InterruptedException, ExecutionException {
-        return delegate.get();
+    public PositionFuture(Runnable runnable, T result, Vector3ic position) {
+        super(runnable, result);
+        this.position = position;
     }
 
-    @Override
-    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException,
-            TimeoutException {
-        return delegate.get(timeout, unit);
+    public Vector3ic getPosition() {
+        return position;
     }
 }