Main.java

package com.taskscheduler;

import java.util.concurrent.TimeUnit;

/**
 * Demonstrates the custom ThreadPool and ScheduledTask system.
 */
public class Main {

    public static void main(String[] args) throws InterruptedException {

        System.out.println("╔══════════════════════════════════════╗");
        System.out.println("║   Custom Thread Pool Task Scheduler  ║");
        System.out.println("╚══════════════════════════════════════╝\n");

        // ── Demo 1: Basic task submission ─────────────────────────────
        System.out.println("--- Demo 1: Basic Task Submission ---");
        ThreadPool pool = new ThreadPool(3, 50);

        for (int i = 1; i <= 6; i++) {
            final int taskNum = i;
            pool.submit("BasicTask-" + i, () -> {
                System.out.printf("  [Task %d] Running on %s%n", taskNum, Thread.currentThread().getName());
                sleep(200);
            });
        }

        Thread.sleep(2000);

        // ── Demo 2: Priority tasks ─────────────────────────────────────
        System.out.println("\n--- Demo 2: Priority Task Ordering ---");
        ThreadPool priorityPool = new ThreadPool(1, 20); // 1 worker so ordering is visible

        // Submit low priority first, high priority last — high should run first
        priorityPool.submit("Low-Priority-Task",    () -> sleep(100), Task.Priority.LOW);
        priorityPool.submit("Low-Priority-Task-2",  () -> sleep(100), Task.Priority.LOW);
        priorityPool.submit("Medium-Priority-Task", () -> sleep(100), Task.Priority.MEDIUM);
        priorityPool.submit("HIGH-PRIORITY-TASK",   () -> sleep(100), Task.Priority.HIGH);
        priorityPool.submit("HIGH-PRIORITY-TASK-2", () -> sleep(100), Task.Priority.HIGH);

        Thread.sleep(1500);
        priorityPool.shutdown();

        // ── Demo 3: Scheduled tasks ────────────────────────────────────
        System.out.println("\n--- Demo 3: Scheduled Tasks ---");
        ThreadPool scheduledPool = new ThreadPool(2);
        ScheduledTask scheduler  = new ScheduledTask(scheduledPool);

        scheduler.scheduleOnce("Delayed-Report", () ->
            System.out.println("  [Delayed-Report] Running 1 second after scheduling!"),
            1, TimeUnit.SECONDS
        );

        scheduler.scheduleRepeating("Heartbeat", () ->
            System.out.println("  [Heartbeat] Ping! " + System.currentTimeMillis()),
            0, 500, TimeUnit.MILLISECONDS
        );

        Thread.sleep(2500);
        scheduler.shutdown();
        scheduledPool.shutdown();

        // ── Demo 4: Stress test ────────────────────────────────────────
        System.out.println("\n--- Demo 4: Stress Test (50 tasks, 4 workers) ---");
        ThreadPool stressPool = new ThreadPool(4, 100);

        long startTime = System.currentTimeMillis();
        for (int i = 1; i <= 50; i++) {
            final int num = i;
            Task.Priority priority = num % 3 == 0 ? Task.Priority.HIGH
                                   : num % 2 == 0 ? Task.Priority.MEDIUM
                                   : Task.Priority.LOW;
            stressPool.submit("StressTask-" + num, () -> sleep(50), priority);
        }

        stressPool.shutdown();
        long elapsed = System.currentTimeMillis() - startTime;
        System.out.printf("Stress test completed in %dms%n", elapsed);

        // ── Final pool shutdown ────────────────────────────────────────
        pool.shutdown();

        System.out.println("\n✅ All demos complete!");
    }

    private static void sleep(long ms) {
        try { Thread.sleep(ms); }
        catch (InterruptedException e) { Thread.currentThread().interrupt(); }
    }
}