Implement simulated core download manager multithreading logic
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# Eighth Assignment: Multithreading Basics
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<div dir="rtl">
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## Table of contents
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- [Introduction](#introduction)
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- [Objectives 🎯](#objectives-)
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- [Theoretical Questions 📝](#theoretical-questions-)
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- [Practical Questions 💻](#practical-questions-)
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- [Evaluation ⚖️](#evaluation-)
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- [Submission ⌛](#submission-)
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- [Additional Resources 📚](#additional-resources-)
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# گزارش پروژه هشتم - برنامهنویسی پیشرفته
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## Important Note:
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This project is configured as a **Maven project**. If you're opening this project in an IDE (like IntelliJ IDEA or VS Code), please ensure you import it as a Maven project so that dependencies and build settings are recognized automatically.
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To run the project from the command line, use:
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```bash
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mvn compile
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mvn exec:java -Dexec.mainClass="Main"
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```
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## Introduction
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Welcome to your Eighth Advanced Programming (AP) Assignment. This project is divided into two main sections:
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1. **Theoretical Questions**: Analyze key multithreading concepts (Start vs Run, Daemon threads, and Lambdas).
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2. **Practical Questions**: Implement a **Simulated Download Manager**. You will use Java Threads to simulate downloading a file in multiple chunks concurrently.
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> **⚠️ Note:** This is a **local simulation only**. There is no actual network activity, URL connection, or socket programming involved. The goal is to practice thread management and state observation.
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## Objectives 🎯
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By completing this assignment, you will:
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- Apply **multithreading** basics using the `Thread` class and `Runnable` interface.
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- Understand how to manage multiple worker threads performing independent tasks.
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- Implement a monitor thread to observe the progress of other threads.
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- Practice using `start()` and `join()` for thread lifecycle management.
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## Theoretical Questions 📝
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**Note: Please answer these questions in a Markdown file (Report.md) and place it in the root directory of your fork. Include code or screenshots where you see fit.**
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### 1. `start()` vs `run()`
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```java
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public class StartVsRun {
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static class MyRunnable implements Runnable {
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public void run() {
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System.out.println("Running in: " + Thread.currentThread().getName());
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}
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}
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public static void main(String[] args) throws InterruptedException {
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Thread t1 = new Thread(new MyRunnable(), "Thread-1");
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System.out.println("Calling run()");
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t1.run();
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Thread.sleep(100);
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Thread t2 = new Thread(new MyRunnable(), "Thread-2");
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System.out.println("Calling start()");
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t2.start();
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}
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}
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```
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**Questions:**
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- What output do you get from the program? Why?
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- What’s the difference in behavior between calling `start()` and `run()`?
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---
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### 2. Daemon Threads
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```java
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public class DaemonExample {
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static class DaemonRunnable implements Runnable {
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public void run() {
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for(int i = 0; i < 20; i++) {
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System.out.println("Daemon thread running...");
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try {
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Thread.sleep(500);
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} catch (InterruptedException e) {
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//[Handling Exception...]
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}
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}
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}
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}
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public static void main(String[] args) {
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Thread thread = new Thread(new DaemonRunnable());
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thread.setDaemon(true);
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thread.start();
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System.out.println("Main thread ends.");
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}
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}
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```
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**Questions:**
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- What output do you get from the program? Why?
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- What happens if you remove `thread.setDaemon(true)`?
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- What are some real-life use cases of daemon threads?
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---
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### 3. A shorter way to create threads
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```java
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public class ThreadDemo {
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public static void main(String[] args) {
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Thread thread = new Thread(() -> {
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System.out.println("Thread is running using a ...!");
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});
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thread.start();
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}
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}
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```
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**Questions:**
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- What output do you get from the program?
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- What is the `() -> { ... }` syntax called?
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- How is this code different from creating a class that extends `Thread` or implements `Runnable`?
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## Practical Questions 💻
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### Simulated Download Manager
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You are tasked with completing a skeleton project for a download manager. The application reads a configuration file, splits a "file" into several chunks, and assigns each chunk to a dedicated worker thread.
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#### 🏗 Project Structure
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- `src/main/resources/download_config.txt`: Contains simulation parameters (file size, chunk count, delays).
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- `DownloadWorker.java`: The logic for simulating a chunk download (needs implementation).
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- `ProgressMonitor.java`: A thread that periodically prints the total progress (needs implementation).
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- `Main.java`: The entry point that initializes chunks, starts threads, and waits for completion.
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- `ChunkStatus.java`: Data class holding the state of individual chunks.
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#### 🛠 What You Need to Do
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In the provided source code, look for **`// TODO`** comments. You must:
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1. **Implement `DownloadWorker`**:
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- Record start/end times for each chunk.
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- Use a loop to simulate progress based on the random delays and step sizes provided in the config.
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- Update the shared `ChunkStatus` object so the monitor can see progress.
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2. **Implement `ProgressMonitor`**:
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- Periodically calculate the total downloaded megabytes across all chunks.
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- Exit gracefully once all chunks are marked as completed.
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3. **Complete `Main`**:
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- Properly instantiate and `start()` the worker threads and the monitor thread.
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- Use `join()` to ensure the main thread waits for all workers to finish before printing the final report.
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#### ⚙️ Configuration
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The simulation behavior is controlled by `src/main/resources/download_config.txt`. You can modify these values to test different scenarios (e.g., more chunks or faster/slower speeds).
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**نام دانشجو:** امیرعلی امیری
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**درس:** برنامهنویسی پیشرفته (AP)
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---
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## Bonus Tasks 🌟
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- Download Speed and ETA:
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- Calculate and display the current overall download speed during the simulation.
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- Estimate and show the remaining time (ETA) based on the current progress and speed.
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## بخش اول: مقایسه `start()` و `run()`
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- User Interface (UI):
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- Improve the console output or design a simple UI that presents download progress in a cleaner and more intuitive way.
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- Make the simulation easier to follow by showing chunk activity, total progress, and final results in a user-friendly format.
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### ۱. خروجی برنامه و دلیل آن
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* **خروجی فراخوانی `t1.run()`:** عبارت `Running in: main`
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* **خروجی فراخوانی `t2.start()`:** عبارت `Running in: Thread-2`
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- Real-Time Progress Bar:
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- Implement a real-time progress bar that updates in place instead of printing a new line each time.
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- Show smooth progress growth in the console so the output looks more like a real download manager.
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**دلیل:** هنگام فراخوانی مستقیم متد `t1.run()`، نخ (Thread) جدیدی ساخته نمیشود؛ به همین دلیل کدهای درون این متد مانند یک متد معمولی و به صورت خطبهخط، داخل همان نخ فعلی (یعنی نخ `main`) اجرا میشوند.
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اما با فراخوانی متد `t2.start()`، به ماشین مجازی جاوا (JVM) درخواست داده میشود تا یک نخ کاملاً جدید و مستقل ایجاد کند. پس از ایجاد این نخ، متد `run()` درون آن و به صورت موازی با نخ اصلی اجرا خواهد شد.
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- Sequential vs Multithreaded Comparison:
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- Add a mode to simulate downloading chunks sequentially (one after another) and compare it with the multithreaded version.
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- Measure and report the total execution time of both approaches, and briefly analyze the difference in performance.
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### ۲. تفاوت رفتاری
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* **متد `start()`:** به صورت غیرهمگام (Asynchronous) عمل میکند. این متد با ایجاد یک Call Stack مجزا برای نخ جدید، امکان اجرای همزمان وظایف مختلف را فراهم میسازد.
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* **متد `run()`:** به صورت همگام (Synchronous) عمل میکند و رفتار آن کاملاً مشابه یک متد عادی است؛ در نتیجه، نخ فعلی را تا زمان اتمام اجرای کدهای خود متوقف (Block) میکند.
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## Evaluation ⚖️
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---
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Your work will be evaluated based on:
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## بخش دوم: نخهای پسزمینه (Daemon Threads)
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- **Thread Management**: Correct use of `start()` and `join()`.
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- **Simulation Logic**: Correct implementation of the loops and random delays in the worker threads.
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- **Thread Safety**: Following the constraint of each worker only writing to its own assigned object.
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- **Code Quality**: Readable code and proper use of Java conventions.
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### ۱. خروجی برنامه و دلیل آن
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* **خروجی:** معمولاً برنامه تنها با چاپ خط `Main thread ends.` پایان مییابد.
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**Total: 500 points**
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- 🧠 Theoretical Questions – 150 points
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- 💻 Practical Task (Download Manager) – 350 points
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**دلیل:** در جاوا، به محض اتمام کار تمامی نخهای کاربر (User Threads یا همان نخهای غیر دیمن)، ماشین مجازی جاوا (JVM) به طور خودکار بسته میشود. از آنجا که نخ `main` بلافاصله پس از فعالسازی نخ دیمن به پایان میرسد، JVM نیز کار برنامه را خاتمه میدهد و منتظر کامل شدن حلقه نخ دیمن نمیماند.
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## Submission ⌛
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### ۲. حذف خط `thread.setDaemon(true)`
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در صورت حذف این خط، نخ به یک نخ کاربر معمولی تبدیل میشود. در این حالت، حتی پس از اتمام کار نخ `main`، ماشین مجازی جاوا روشن باقی میماند و منتظر میشود تا این نخ تمام ۲۰ دور حلقه خود را (که حدود ۱۰ ثانیه زمان میبرد) به طور کامل اجرا کند.
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1. Add your mentor as a contributor to the project.
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2. Create a `develop` branch for implementing features.
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3. Use Git for regular code commits.
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4. Push your code and the answers file (Report.md) to the remote repository.
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5. Submit a pull request to merge the `develop` branch with `main`.
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### ۳. کاربردهای واقعی نخهای Daemon
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* **سیستم زبالهروبی جاوا (Garbage Collection):** مدیریت و آزادسازی حافظه بلااستفاده در پسزمینه برنامه.
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* **نخهای مانیتورینگ:** بررسی مداوم وضعیت سلامت و میزان مصرف منابع سیستم در پسزمینه.
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* **سیستم ذخیره خودکار (Auto-Save):** ذخیرهسازی دورهای اطلاعات در بازیها یا نرمافزارهای ویرایشگر، بدون ایجاد وقفه در جریان اصلی برنامه.
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**Deadline:** **Friday, June 5** (15th of Khordad)
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---
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## Additional Resources 📚
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## بخش سوم: روش کوتاهتر برای ساخت نخها (Lambda Expression)
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- [Java Concurrency and Multithreading](https://jenkov.com/tutorials/java-concurrency/index.html)
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- [Creating and Starting Java Threads](https://jenkov.com/tutorials/java-concurrency/creating-and-starting-threads.html)
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- [Thread.join() explained](https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html#join--)
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### ۱. خروجی برنامه
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* **خروجی:** عبارت `Thread is running using a ...!` در کنسول چاپ میشود.
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### ۲. نام این سینتکس
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به سینتکس `() -> { ... }` اصطلاحاً **Lambda Expression** (عبارت لمبدا) میگویند.
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### ۳. تفاوت با روشهای سنتی
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در روشهای سنتی باید یک کلاس مجزا به صورت مشتقشده از `Thread` ایجاد میکردیم یا اینترفیس `Runnable` را از طریق یک کلاس جداگانه یا بینام (Anonymous Class) پیادهسازی مینمودیم. اما با استفاده از عبارت لمبدا، نیازی به نوشتن این کدهای تکراری و اضافی نیست و میتوان پیادهسازی تنها متد انتزاعی اینترفیس (یعنی متد `run`) را به صورت مستقیم و خلاصه به سازنده کلاس `Thread` پاس داد. این کار خوانایی کد را افزایش میدهد، در حالی که عملکرد آن در پشت صحنه هیچ تفاوتی با روشهای گذشته ندارد.
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</div>
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