Re-implement scheduler system (check #1321)

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

@@ -0,0 +1,148 @@
+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;
+    }
+}