Rewrote scheduler to use ScheduledExecutorService for delay/repeat tasks

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -25,7 +25,6 @@ import com.velocitypowered.proxy.messages.VelocityChannelRegistrar;
 import com.velocitypowered.proxy.plugin.VelocityEventManager;
 import com.velocitypowered.proxy.protocol.util.FaviconSerializer;
 import com.velocitypowered.proxy.plugin.VelocityPluginManager;
-import com.velocitypowered.proxy.scheduler.Sleeper;
 import com.velocitypowered.proxy.scheduler.VelocityScheduler;
 import com.velocitypowered.proxy.util.AddressUtil;
 import com.velocitypowered.proxy.util.EncryptionUtils;
@@ -137,7 +136,7 @@ public class VelocityServer implements ProxyServer {
         ipAttemptLimiter = new Ratelimiter(configuration.getLoginRatelimit());
         httpClient = new NettyHttpClient(this);
         eventManager = new VelocityEventManager(pluginManager);
-        scheduler = new VelocityScheduler(pluginManager, Sleeper.SYSTEM);
+        scheduler = new VelocityScheduler(pluginManager);
         channelRegistrar = new VelocityChannelRegistrar();
         loadPlugins();
 

proxy/src/main/java/com/velocitypowered/proxy/scheduler/Sleeper.java

@@ -1,7 +0,0 @@
-package com.velocitypowered.proxy.scheduler;
-
-public interface Sleeper {
-    void sleep(long ms) throws InterruptedException;
-
-    Sleeper SYSTEM = Thread::sleep;
-}

proxy/src/main/java/com/velocitypowered/proxy/scheduler/VelocityScheduler.java

@@ -14,22 +14,22 @@ import org.apache.logging.log4j.Logger;
 
 import java.util.ArrayList;
 import java.util.IdentityHashMap;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
-import java.util.concurrent.TimeUnit;
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicReference;
 
 public class VelocityScheduler implements Scheduler {
     private final PluginManager pluginManager;
     private final ExecutorService taskService;
-    private final Sleeper sleeper;
+    private final ScheduledExecutorService timerExecutionService;
     private final Multimap<Object, ScheduledTask> tasksByPlugin = Multimaps.synchronizedListMultimap(
             Multimaps.newListMultimap(new IdentityHashMap<>(), ArrayList::new));
 
-    public VelocityScheduler(PluginManager pluginManager, Sleeper sleeper) {
+    public VelocityScheduler(PluginManager pluginManager) {
         this.pluginManager = pluginManager;
-        this.sleeper = sleeper;
         this.taskService = Executors.newCachedThreadPool(new ThreadFactoryBuilder().setDaemon(true)
                 .setNameFormat("Velocity Task Scheduler - #%d").build());
+        this.timerExecutionService = Executors.newSingleThreadScheduledExecutor(new ThreadFactoryBuilder().setDaemon(true)
+                .setNameFormat("Velocity Task Scheduler Timer").build());
     }
 
     @Override
@@ -44,6 +44,7 @@ public class VelocityScheduler implements Scheduler {
         for (ScheduledTask task : ImmutableList.copyOf(tasksByPlugin.values())) {
             task.cancel();
         }
+        timerExecutionService.shutdown();
         taskService.shutdown();
         return taskService.awaitTermination(10, TimeUnit.SECONDS);
     }
@@ -85,27 +86,30 @@ public class VelocityScheduler implements Scheduler {
 
         @Override
         public ScheduledTask schedule() {
-            VelocityTask task = new VelocityTask(plugin, runnable, delay, repeat);
+            if (delay == 0 && repeat == 0) {
+                // A special purpose, simplified implementation
+                VelocityImmediatelyScheduledTask task = new VelocityImmediatelyScheduledTask(plugin, runnable);
+                tasksByPlugin.put(plugin, task);
                 taskService.execute(task);
+                return task;
+            } else {
+                VelocityTask task = new VelocityTask(plugin, runnable, delay, repeat);
                 tasksByPlugin.put(plugin, task);
                 return task;
             }
         }
+    }
 
-    private class VelocityTask implements Runnable, ScheduledTask {
+    private class VelocityImmediatelyScheduledTask implements ScheduledTask, Runnable {
         private final Object plugin;
         private final Runnable runnable;
-        private final long delay;
-        private final long repeat;
-        private volatile TaskStatus status;
+        private final AtomicReference<TaskStatus> status;
         private Thread taskThread;
 
-        private VelocityTask(Object plugin, Runnable runnable, long delay, long repeat) {
+        private VelocityImmediatelyScheduledTask(Object plugin, Runnable runnable) {
             this.plugin = plugin;
             this.runnable = runnable;
-            this.delay = delay;
-            this.repeat = repeat;
-            this.status = TaskStatus.SCHEDULED;
+            this.status = new AtomicReference<>(TaskStatus.SCHEDULED);
         }
 
         @Override
@@ -115,13 +119,12 @@ public class VelocityScheduler implements Scheduler {
 
         @Override
         public TaskStatus status() {
-            return status;
+            return status.get();
         }
 
         @Override
         public void cancel() {
-            if (status == TaskStatus.SCHEDULED) {
-                status = TaskStatus.CANCELLED;
+            if (status.compareAndSet(TaskStatus.SCHEDULED, TaskStatus.CANCELLED)) {
                 if (taskThread != null) {
                     taskThread.interrupt();
                 }
@@ -131,40 +134,75 @@ public class VelocityScheduler implements Scheduler {
         @Override
         public void run() {
             taskThread = Thread.currentThread();
-            if (delay > 0) {
-                try {
-                    sleeper.sleep(delay);
-                } catch (InterruptedException e) {
-                    if (status == TaskStatus.CANCELLED) {
-                        onFinish();
-                        return;
-                    }
-                }
-            }
-
-            while (status != TaskStatus.CANCELLED) {
             try {
                 runnable.run();
             } catch (Exception e) {
                 Log.logger.error("Exception in task {} by plugin {}", runnable, plugin);
             }
+            status.compareAndSet(TaskStatus.SCHEDULED, TaskStatus.FINISHED);
+            taskThread = null;
+            tasksByPlugin.remove(plugin, this);
+        }
+    }
 
-                if (repeat > 0) {
-                    try {
-                        sleeper.sleep(repeat);
-                    } catch (InterruptedException e) {
-                        if (status == TaskStatus.CANCELLED) {
-                            break;
-                        }
-                    }
+    private class VelocityTask implements Runnable, ScheduledTask {
+        private final Object plugin;
+        private final Runnable runnable;
+        private ScheduledFuture<?> future;
+
+        private VelocityTask(Object plugin, Runnable runnable, long delay, long repeat) {
+            this.plugin = plugin;
+            this.runnable = runnable;
+            if (repeat == 0) {
+                this.future = timerExecutionService.schedule(this, delay, TimeUnit.MILLISECONDS);
             } else {
-                    status = TaskStatus.FINISHED;
-                    break;
+                this.future = timerExecutionService.scheduleAtFixedRate(this, delay, repeat, TimeUnit.MILLISECONDS);
             }
         }
 
+        @Override
+        public Object plugin() {
+            return plugin;
+        }
+
+        @Override
+        public TaskStatus status() {
+            if (future == null) {
+                return TaskStatus.SCHEDULED;
+            }
+
+            if (future.isCancelled()) {
+                return TaskStatus.CANCELLED;
+            }
+
+            if (future.isDone()) {
+                return TaskStatus.FINISHED;
+            }
+
+            return TaskStatus.SCHEDULED;
+        }
+
+        @Override
+        public void cancel() {
+            if (future != null) {
+                future.cancel(true);
                 onFinish();
             }
+        }
+
+        @Override
+        public void run() {
+            try {
+                runnable.run();
+            } catch (Exception e) {
+                // Since we can't catch InterruptedException separately...
+                if (e instanceof InterruptedException) {
+                    onFinish();
+                } else {
+                    Log.logger.error("Exception in task {} by plugin {}", runnable, plugin);
+                }
+            }
+        }
 
         private void onFinish() {
             tasksByPlugin.remove(plugin, this);

proxy/src/test/java/com/velocitypowered/proxy/scheduler/VelocitySchedulerTest.java

@@ -16,7 +16,7 @@ class VelocitySchedulerTest {
 
     @Test
     void buildTask() throws Exception {
-        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager(), Sleeper.SYSTEM);
+        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager());
         CountDownLatch latch = new CountDownLatch(1);
         ScheduledTask task = scheduler.buildTask(FakePluginManager.PLUGIN_A, latch::countDown).schedule();
         latch.await();
@@ -25,7 +25,7 @@ class VelocitySchedulerTest {
 
     @Test
     void cancelWorks() throws Exception {
-        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager(), Sleeper.SYSTEM);
+        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager());
         AtomicInteger i = new AtomicInteger(3);
         ScheduledTask task = scheduler.buildTask(FakePluginManager.PLUGIN_A, i::decrementAndGet)
                 .delay(100, TimeUnit.SECONDS)
@@ -38,7 +38,7 @@ class VelocitySchedulerTest {
 
     @Test
     void repeatTaskWorks() throws Exception {
-        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager(), Sleeper.SYSTEM);
+        VelocityScheduler scheduler = new VelocityScheduler(new FakePluginManager());
         CountDownLatch latch = new CountDownLatch(3);
         ScheduledTask task = scheduler.buildTask(FakePluginManager.PLUGIN_A, latch::countDown)
                 .delay(100, TimeUnit.MILLISECONDS)