Re-implement scheduler system (check #1321)

src/main/java/emu/grasscutter/server/event/game/ServerTickEvent.java

 package emu.grasscutter.server.event.game;
 
 import emu.grasscutter.server.event.types.ServerEvent;
+import java.time.Instant;
+
+import java.time.Instant;
 
 public final class ServerTickEvent extends ServerEvent {
-    public ServerTickEvent() {
+    private final Instant start, end;
+
+    public ServerTickEvent(Instant start, Instant end) {
         super(Type.GAME);
+
+        this.start = start;
+        this.end = end;
+    }
+
+    public Instant getTickStart() {
+        return this.start;
+    }
+
+    public Instant getTickEnd() {
+        return this.end;
+    }
+
+    public Instant getTickStart() {
+        return this.start;
+    }
+
+    public Instant getTickEnd() {
+        return this.end;
     }
 }
\ No newline at end of file

src/main/java/emu/grasscutter/server/game/GameServer.java

@@ -26,11 +26,14 @@ import emu.grasscutter.server.event.types.ServerEvent;
 import emu.grasscutter.server.event.game.ServerTickEvent;
 import emu.grasscutter.server.event.internal.ServerStartEvent;
 import emu.grasscutter.server.event.internal.ServerStopEvent;
+import emu.grasscutter.server.scheduler.ServerTaskScheduler;
 import emu.grasscutter.task.TaskMap;
 import kcp.highway.ChannelConfig;
 import kcp.highway.KcpServer;
+import lombok.Getter;
 
 import java.net.InetSocketAddress;
+import java.time.Instant;
 import java.time.OffsetDateTime;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
@@ -42,6 +45,7 @@ public final class GameServer extends KcpServer {
 	private final InetSocketAddress address;
 	private final GameServerPacketHandler packetHandler;
 	private final ServerQuestHandler questHandler;
+    @Getter private final ServerTaskScheduler scheduler;
 
 	private final Map<Integer, Player> players;
 	private final Set<World> worlds;
@@ -80,6 +84,7 @@ public final class GameServer extends KcpServer {
 		this.address = address;
 		this.packetHandler = new GameServerPacketHandler(PacketHandler.class);
 		this.questHandler = new ServerQuestHandler();
+        this.scheduler = new ServerTaskScheduler();
 		this.players = new ConcurrentHashMap<>();
 		this.worlds = Collections.synchronizedSet(new HashSet<>());
 
@@ -238,7 +243,10 @@ public final class GameServer extends KcpServer {
 		return DatabaseHelper.getAccountByName(username);
 	}
 
-	public synchronized void onTick(){
+    public synchronized void onTick() {
+        var tickStart = Instant.now();
+
+        // Tick worlds.
         Iterator<World> it = this.getWorlds().iterator();
         while (it.hasNext()) {
             World world = it.next();
@@ -250,11 +258,17 @@ public final class GameServer extends KcpServer {
             world.onTick();
         }
 
+        // Tick players.
         for (Player player : this.getPlayers().values()) {
             player.onTick();
         }
 
-		ServerTickEvent event = new ServerTickEvent(); event.call();
+        // Tick scheduler.
+        this.getScheduler().runTasks();
+
+        // Call server tick event.
+        ServerTickEvent event = new ServerTickEvent(tickStart, Instant.now());
+        event.call();
     }
 
 	public void registerWorld(World world) {

src/main/java/emu/grasscutter/server/scheduler/AsyncServerTask.java

+package emu.grasscutter.server.scheduler;
+
+import lombok.Getter;
+
+import javax.annotation.Nullable;
+
+/**
+ * A server task that should be run asynchronously.
+ */
+public final class AsyncServerTask implements Runnable {
+    /* The runnable to run. */
+    private final Runnable task;
+    /* This ID is assigned by the scheduler. */
+    @Getter private final int taskId;
+    /* The result callback to run. */
+    @Nullable private final Runnable callback;
+
+    /* Has the task already been started? */
+    private boolean started = false;
+    /* Has the task finished execution? */
+    private boolean finished = false;
+    /* The result produced in the async task. */
+    @Nullable private Object result = null;
+
+    /**
+     * For tasks without a callback.
+     * @param task The task to run.
+     */
+    public AsyncServerTask(Runnable task, int taskId) {
+        this(task, null, taskId);
+    }
+
+    /**
+     * For tasks with a callback.
+     * @param task The task to run.
+     * @param callback The task to run after the task is complete.
+     */
+    public AsyncServerTask(Runnable task, @Nullable Runnable callback, int taskId) {
+        this.task = task;
+        this.callback = callback;
+        this.taskId = taskId;
+    }
+
+    /**
+     * Returns the state of the task.
+     * @return True if the task has been started, false otherwise.
+     */
+    public boolean hasStarted() {
+        return this.started;
+    }
+
+    /**
+     * Returns the state of the task.
+     * @return True if the task has finished execution, false otherwise.
+     */
+    public boolean isFinished() {
+        return this.finished;
+    }
+
+    /**
+     * Runs the task.
+     */
+    @Override public void run() {
+        // Declare the task as started.
+        this.started = true;
+
+        // Run the runnable.
+        this.task.run();
+
+        // Declare the task as finished.
+        this.finished = true;
+    }
+
+    /**
+     * Runs the callback.
+     */
+    public void complete() {
+        // Run the callback.
+        if(this.callback != null)
+            this.callback.run();
+    }
+
+    /**
+     * Sets the result of the async task.
+     * @param result The result of the async task.
+     */
+    public void setResult(@Nullable Object result) {
+        this.result = result;
+    }
+
+    /**
+     * Returns the set result of the async task.
+     * @return The result, or null if it has not been set.
+     */
+    @Nullable public Object getResult() {
+        return this.result;
+    }
+}

src/main/java/emu/grasscutter/server/scheduler/ServerTask.java

+package emu.grasscutter.server.scheduler;
+
+import emu.grasscutter.Grasscutter;
+import lombok.*;
+
+/**
+ * This class works the same as a runnable, except with more information.
+ */
+public final class ServerTask implements Runnable {
+    /* The runnable to run. */
+    private final Runnable runnable;
+    /* This ID is assigned by the scheduler. */
+    @Getter private final int taskId;
+    /* The period at which the task should be run. */
+    /* The delay between the first execute. */
+    private final int period, delay;
+
+    public ServerTask(Runnable runnable, int taskId, int period, int delay) {
+        this.runnable = runnable;
+        this.taskId = taskId;
+        this.period = period;
+        this.delay = delay;
+    }
+
+    /* The amount of times the task has been run. */
+    @Getter private int ticks = 0;
+    /* Should the check consider delay? */
+    private boolean considerDelay = true;
+
+    /**
+     * Cancels the task from running the next time.
+     */
+    public void cancel() {
+        Grasscutter.getGameServer().getScheduler().cancelTask(this.taskId);
+    }
+
+    /**
+     * Checks if the task should run at the current tick.
+     * @return True if the task should run, false otherwise.
+     */
+    public boolean shouldRun() {
+        if(this.delay != -1 && this.considerDelay) {
+            this.considerDelay = false;
+            return this.ticks == this.delay;
+        } else if(this.period != -1)
+            return this.ticks % this.period == 0;
+        else return true;
+    }
+
+    /**
+     * Checks if the task should be canceled.
+     * @return True if the task should be canceled, false otherwise.
+     */
+    public boolean shouldCancel() {
+        return this.period == -1;
+    }
+
+    /**
+     * Runs the task.
+     */
+    @Override public void run() {
+        // Run the runnable.
+        this.runnable.run();
+        // Increase tick count.
+        this.ticks++;
+    }
+}
\ No newline at end of file

src/main/java/emu/grasscutter/server/scheduler/ServerTaskScheduler.java

+package emu.grasscutter.server.scheduler;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A class to manage all time-based tasks scheduled on the server.
+ * This handles both synchronous and asynchronous tasks.
+ *
+ * Developers note: A server tick is ONE REAL-TIME SECOND.
+ */
+public final class ServerTaskScheduler {
+    /* A map to contain all running tasks. */
+    private final ConcurrentHashMap<Integer, ServerTask> tasks
+        = new ConcurrentHashMap<>();
+    /* A map to contain all async tasks. */
+    private final ConcurrentHashMap<Integer, AsyncServerTask> asyncTasks
+        = new ConcurrentHashMap<>();
+
+    /* The ID assigned to the next runnable. */
+    private int nextTaskId = 0;
+
+    /**
+     * Ran every server tick.
+     * Attempts to run all scheduled tasks.
+     * This method is synchronous and will block until all tasks are complete.
+     */
+    public void runTasks() {
+        // Skip if there are no tasks.
+        if(this.tasks.size() == 0)
+            return;
+
+        // Run all tasks.
+        for(ServerTask task : this.tasks.values()) {
+            // Check if the task should run.
+            if (task.shouldRun()) {
+                // Run the task.
+                task.run();
+            }
+
+            // Check if the task should be canceled.
+            if (task.shouldCancel()) {
+                // Cancel the task.
+                this.cancelTask(task.getTaskId());
+            }
+        }
+
+        // Run all async tasks.
+        for(AsyncServerTask task : this.asyncTasks.values()) {
+            if(!task.hasStarted()) {
+                // Create a thread for the task.
+                Thread thread = new Thread(task);
+                // Start the thread.
+                thread.start();
+            } else if(task.isFinished()) {
+                // Cancel the task.
+                this.asyncTasks.remove(task.getTaskId());
+                // Run the task's callback.
+                task.complete();
+            }
+        }
+    }
+
+    /**
+     * Gets a task from the scheduler.
+     * @param taskId The ID of the task to get.
+     * @return The task, or null if it does not exist.
+     */
+    public ServerTask getTask(int taskId) {
+        return this.tasks.get(taskId);
+    }
+
+    /**
+     * Gets an async task from the scheduler.
+     * @param taskId The ID of the task to get.
+     * @return The task, or null if it does not exist.
+     */
+    public AsyncServerTask getAsyncTask(int taskId) {
+        return this.asyncTasks.get(taskId);
+    }
+
+    /**
+     * Removes a task from the scheduler.
+     * @param taskId The ID of the task to remove.
+     */
+    public void cancelTask(int taskId) {
+        this.tasks.remove(taskId);
+    }
+
+    /**
+     * Schedules a task to be run on a separate thread.
+     * The task runs on the next server tick.
+     * @param runnable The runnable to run.
+     * @return The ID of the task.
+     */
+    public int scheduleAsyncTask(Runnable runnable) {
+        // Get the next task ID.
+        var taskId = this.nextTaskId++;
+        // Create a new task.
+        this.asyncTasks.put(taskId, new AsyncServerTask(runnable, taskId));
+        // Return the task ID.
+        return taskId;
+    }
+
+    /**
+     * Schedules a task to be run on the next server tick.
+     * @param runnable The runnable to run.
+     * @return The ID of the task.
+     */
+    public int scheduleTask(Runnable runnable) {
+        return this.scheduleDelayedRepeatingTask(runnable, -1, -1);
+    }
+
+    /**
+     * Schedules a task to be run after the amount of ticks has passed.
+     * @param runnable The runnable to run.
+     * @param delay The amount of ticks to wait before running.
+     * @return The ID of the task.
+     */
+    public int scheduleDelayedTask(Runnable runnable, int delay) {
+        return this.scheduleDelayedRepeatingTask(runnable, -1, delay);
+    }
+
+    /**
+     * Schedules a task to be run every amount of ticks.
+     * @param runnable The runnable to run.
+     * @param period The amount of ticks to wait before running again.
+     * @return The ID of the task.
+     */
+    public int scheduleRepeatingTask(Runnable runnable, int period) {
+        return this.scheduleDelayedRepeatingTask(runnable, period, 0);
+    }
+
+    /**
+     * Schedules a task to be run after the amount of ticks has passed.
+     * @param runnable The runnable to run.
+     * @param period The amount of ticks to wait before running again.
+     * @param delay The amount of ticks to wait before running the first time.
+     * @return The ID of the task.
+     */
+    public int scheduleDelayedRepeatingTask(Runnable runnable, int period, int delay) {
+        // Get the next task ID.
+        var taskId = this.nextTaskId++;
+        // Create a new task.
+        this.tasks.put(taskId, new ServerTask(runnable, taskId, period, delay));
+        // Return the task ID.
+        return taskId;
+    }
+}
\ No newline at end of file