Improve tick scheduling

src/main/java/net/minestom/server/UpdateManager.java

@@ -108,16 +108,8 @@ public final class UpdateManager {
         // Tick all instances
         MinecraftServer.getInstanceManager().getInstances().forEach(instance ->
                 instance.tick(tickStart));
-
         // Tick all chunks (and entities inside)
-        final CountDownLatch countDownLatch = threadProvider.update(tickStart);
-
-        // Wait tick end
-        try {
-            countDownLatch.await();
-        } catch (InterruptedException e) {
-            e.printStackTrace();
-        }
+        this.threadProvider.updateAndAwait(tickStart);
 
         // Clear removed entities & update threads
         long tickTime = System.currentTimeMillis() - tickStart;

src/main/java/net/minestom/server/acquirable/Acquirable.java

@@ -20,6 +20,8 @@ public interface Acquirable<T> {
      * Gets all the {@link Entity entities} being ticked in the current thread.
      * <p>
      * Useful when you want to ensure that no acquisition is ever done.
+     * <p>
+     * Be aware that the entity stream is only updated at the beginning of the thread tick.
      *
      * @return the entities ticked in the current thread
      */

src/main/java/net/minestom/server/thread/ThreadProvider.java

@@ -11,7 +11,7 @@ import org.jetbrains.annotations.NotNull;
 
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Phaser;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.function.Function;
 
@@ -30,6 +30,8 @@ public abstract class ThreadProvider {
     private final Set<Entity> updatableEntities = ConcurrentHashMap.newKeySet();
     private final Set<Entity> removedEntities = ConcurrentHashMap.newKeySet();
 
+    private final Phaser phaser = new Phaser(1);
+
     public ThreadProvider(int threadCount) {
         this.threads = new ArrayList<>(threadCount);
 
@@ -112,24 +114,23 @@ public abstract class ThreadProvider {
      *
      * @param time the tick time in milliseconds
      */
-    public synchronized @NotNull CountDownLatch update(long time) {
-        CountDownLatch countDownLatch = new CountDownLatch(threads.size());
-        for (TickThread thread : threads) {
+    public void updateAndAwait(long time) {
+        for (var entry : threadChunkMap.entrySet()) {
+            final TickThread thread = entry.getKey();
+            final var chunkEntries = entry.getValue();
+            if (chunkEntries == null || chunkEntries.isEmpty()) {
+                // Nothing to tick
+                continue;
+            }
             // Execute tick
-            thread.runnable.startTick(countDownLatch, () -> {
-                final var chunkEntries = threadChunkMap.get(thread);
-                if (chunkEntries == null || chunkEntries.isEmpty()) {
-                    // Nothing to tick
-                    Acquirable.refreshEntries(Collections.emptySet());
-                    return;
-                }
-
+            this.phaser.register();
+            thread.runnable.startTick(phaser, () -> {
                 Acquirable.refreshEntries(chunkEntries);
 
                 final ReentrantLock lock = thread.getLock();
                 lock.lock();
                 chunkEntries.forEach(chunkEntry -> {
-                    Chunk chunk = chunkEntry.chunk;
+                    final Chunk chunk = chunkEntry.chunk;
                     if (!ChunkUtils.isLoaded(chunk))
                         return;
                     chunk.tick(time);
@@ -138,18 +139,18 @@ public abstract class ThreadProvider {
                         for (Entity entity : entities) {
                             if (lock.hasQueuedThreads()) {
                                 lock.unlock();
-                                // #acquire callbacks should be called here
+                                // #acquire() callbacks should be called here
                                 lock.lock();
                             }
                             entity.tick(time);
                         }
                     }
                 });
-                Acquirable.refreshEntries(Collections.emptySet());
                 lock.unlock();
+                // #acquire() callbacks
             });
         }
-        return countDownLatch;
+        this.phaser.arriveAndAwaitAdvance();
     }
 
     /**

src/main/java/net/minestom/server/thread/TickThread.java

@@ -4,7 +4,7 @@ import net.minestom.server.MinecraftServer;
 import net.minestom.server.utils.validate.Check;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Phaser;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 import java.util.concurrent.locks.LockSupport;
 import java.util.concurrent.locks.ReentrantLock;
@@ -60,16 +60,16 @@ public class TickThread extends Thread {
                 // The context is necessary to control the tick rates
                 if (localContext != null) {
                     // Execute tick
-                    localContext.runnable.run();
-                    localContext.countDownLatch.countDown();
                     CONTEXT_UPDATER.compareAndSet(this, localContext, null);
+                    localContext.runnable.run();
+                    localContext.phaser.arriveAndDeregister();
                 }
                 LockSupport.park(this);
             }
         }
 
-        protected void startTick(@NotNull CountDownLatch countDownLatch, @NotNull Runnable runnable) {
-            this.tickContext = new TickContext(countDownLatch, runnable);
+        protected void startTick(@NotNull Phaser phaser, @NotNull Runnable runnable) {
+            this.tickContext = new TickContext(phaser, runnable);
             LockSupport.unpark(tickThread);
         }
 
@@ -79,11 +79,11 @@ public class TickThread extends Thread {
     }
 
     private static class TickContext {
-        private final CountDownLatch countDownLatch;
+        private final Phaser phaser;
         private final Runnable runnable;
 
-        private TickContext(@NotNull CountDownLatch countDownLatch, @NotNull Runnable runnable) {
-            this.countDownLatch = countDownLatch;
+        private TickContext(@NotNull Phaser phaser, @NotNull Runnable runnable) {
+            this.phaser = phaser;
             this.runnable = runnable;
         }
     }