8th Home Work, Practical and Theoretical Questions

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+\documentclass[12pt,a4paper]{article}
+
+\usepackage[utf8]{inputenc}
+\usepackage[T1]{fontenc}
+\usepackage[margin=2.5cm]{geometry}
+\usepackage{listings}
+\usepackage{xcolor}
+\usepackage{hyperref}
+\usepackage{parskip}
+\usepackage{booktabs}
+\usepackage{array}
+\usepackage{titlesec}
+\usepackage{fancyhdr}
+\usepackage{amsmath}
+\usepackage{enumitem}
+
+% ── Page style ──────────────────────────────────────────────────────────────
+\pagestyle{fancy}
+\fancyhf{}
+\rhead{Advanced Programming – Assignment 8}
+\lhead{Faraz Ardeh}
+\cfoot{\thepage}
+
+% ── Section formatting ───────────────────────────────────────────────────────
+\titleformat{\section}{\large\bfseries}{Question \thesection.}{0.6em}{}
+\titleformat{\subsection}{\normalsize\bfseries}{}{0em}{}
+
+% ── Java code style ─────────────────────────────────────────────────────────
+\definecolor{javakw}{rgb}{0.13,0.13,0.60}
+\definecolor{javastr}{rgb}{0.63,0.13,0.13}
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+\definecolor{codebg}{rgb}{0.97,0.97,0.97}
+\definecolor{codefr}{rgb}{0.82,0.82,0.82}
+
+\lstdefinestyle{java}{
+    language=Java,
+    basicstyle=\ttfamily\small,
+    keywordstyle=\color{javakw}\bfseries,
+    stringstyle=\color{javastr},
+    commentstyle=\color{javacmt}\itshape,
+    numberstyle=\tiny\color{gray},
+    numbers=left,
+    stepnumber=1,
+    numbersep=8pt,
+    backgroundcolor=\color{codebg},
+    frame=single,
+    rulecolor=\color{codefr},
+    breaklines=true,
+    breakatwhitespace=false,
+    showstringspaces=false,
+    tabsize=4,
+    captionpos=b,
+}
+
+\lstset{style=java}
+
+% ── Inline code ─────────────────────────────────────────────────────────────
+\newcommand{\code}[1]{\texttt{\small #1}}
+
+% ────────────────────────────────────────────────────────────────────────────
+\begin{document}
+
+% ── Title page ───────────────────────────────────────────────────────────────
+\begin{titlepage}
+    \centering
+    \vspace*{3cm}
+    {\Huge\bfseries Multithreading Basics\par}
+    \vspace{0.8cm}
+    {\large Assignment 8 – Theoretical Questions\par}
+    \vspace{0.4cm}
+    {\large Advanced Programming (AP)\par}
+    \vspace{2cm}
+    \rule{0.6\linewidth}{0.5pt}\\[0.4cm]
+    {\large\bfseries Faraz Ardeh\par}
+    \vspace{0.3cm}
+    {\normalsize fa.ardeh@gmail.com\par}
+    \vspace{0.6cm}
+    {\normalsize Shahid Beheshti University\par}
+    \vspace{0.3cm}
+    {\normalsize June 2026\par}
+    \vfill
+\end{titlepage}
+
+\tableofcontents
+\newpage
+
+% ════════════════════════════════════════════════════════════════════════════
+\section{\code{start()} vs \code{run()}}
+% ════════════════════════════════════════════════════════════════════════════
+
+The program under analysis:
+
+\begin{lstlisting}[caption={StartVsRun.java}]
+public class StartVsRun {
+    static class MyRunnable implements Runnable {
+        public void run() {
+            System.out.println("Running in: " + Thread.currentThread().getName());
+        }
+    }
+    public static void main(String[] args) throws InterruptedException {
+        Thread t1 = new Thread(new MyRunnable(), "Thread-1");
+        System.out.println("Calling run()");
+        t1.run();
+        Thread.sleep(100);
+
+        Thread t2 = new Thread(new MyRunnable(), "Thread-2");
+        System.out.println("Calling start()");
+        t2.start();
+    }
+}
+\end{lstlisting}
+
+\subsection{Expected output}
+
+\begin{lstlisting}[language={},numbers=none,backgroundcolor=\color{codebg}]
+Calling run()
+Running in: main
+Calling start()
+Running in: Thread-2
+\end{lstlisting}
+
+\subsection{Why this output?}
+
+\textbf{The \code{t1.run()} call:}
+Calling \code{run()} on a \code{Thread} object is just an ordinary method call, exactly
+like calling any other method on any other object.
+No new OS thread is created or scheduled.
+The body of \code{run()} executes \emph{synchronously} inside the calling thread,
+which is \code{main}.
+Therefore \code{Thread.currentThread().getName()} returns \texttt{"main"},
+not \texttt{"Thread-1"}.
+The thread object \texttt{t1} was constructed but its native thread was never started.
+
+\textbf{The \code{t2.start()} call:}
+\code{start()} allocates a new OS-level thread, registers it with the JVM scheduler,
+and returns to the caller \emph{immediately} (it does not wait for \code{run()} to finish).
+The new thread then invokes \code{run()} autonomously and concurrently.
+Inside that new thread, \code{Thread.currentThread().getName()} correctly
+returns \texttt{"Thread-2"}.
+
+\subsection{Key differences at a glance}
+
+\begin{center}
+\begin{tabular}{>{\bfseries}lll}
+\toprule
+Aspect & \code{run()} & \code{start()} \\
+\midrule
+New thread created?   & No  & Yes (exactly one) \\
+Execution thread      & Current thread & New thread \\
+Blocking behaviour    & Synchronous (caller waits) & Asynchronous (returns at once) \\
+Can be called twice?  & Yes, legal & No – throws \code{IllegalThreadStateException} \\
+Useful for?           & Testing \code{run()} logic directly & True concurrent execution \\
+\bottomrule
+\end{tabular}
+\end{center}
+
+\textbf{Summary:}
+\code{run()} is simply a method call; \code{start()} is what actually creates and
+launches a new thread of execution. Calling \code{run()} instead of \code{start()} is
+one of the most common multithreading bugs in Java – the code compiles and
+"works", but no concurrency ever happens.
+
+% ════════════════════════════════════════════════════════════════════════════
+\section{Daemon Threads}
+% ════════════════════════════════════════════════════════════════════════════
+
+\begin{lstlisting}[caption={DaemonExample.java}]
+public class DaemonExample {
+    static class DaemonRunnable implements Runnable {
+        public void run() {
+            for (int i = 0; i < 20; i++) {
+                System.out.println("Daemon thread running...");
+                try {
+                    Thread.sleep(500);
+                } catch (InterruptedException e) {
+                    // [Handling Exception...]
+                }
+            }
+        }
+    }
+    public static void main(String[] args) {
+        Thread thread = new Thread(new DaemonRunnable());
+        thread.setDaemon(true);
+        thread.start();
+        System.out.println("Main thread ends.");
+    }
+}
+\end{lstlisting}
+
+\subsection{Expected output (with \code{setDaemon(true)})}
+
+\begin{lstlisting}[language={},numbers=none,backgroundcolor=\color{codebg}]
+Main thread ends.
+Daemon thread running...
+(program terminates -- usually 0-2 more lines, non-deterministic)
+\end{lstlisting}
+
+\textbf{Why?}
+The JVM shuts down when there are no \emph{non-daemon} threads still alive.
+After \code{main()} prints \texttt{"Main thread ends."} and returns, the only surviving
+thread is the daemon thread.
+Because it is marked as a daemon, the JVM does \emph{not} wait for it to
+finish – it exits immediately (or after one scheduling quantum), abruptly
+terminating the daemon thread.
+The daemon may manage to print zero, one, or a few lines before termination,
+depending entirely on OS thread scheduling; this is non-deterministic.
+
+\subsection{What happens if you remove \code{thread.setDaemon(true)}?}
+
+Without that call the thread becomes a regular \emph{user thread} (the default).
+The JVM rule is: \textbf{wait for all user threads to finish before exiting.}
+The daemon thread (now a user thread) will sleep 500 ms per iteration and
+loop 20 times – the program will take approximately $20 \times 0.5 = 10$ seconds
+to terminate, and all 20 lines of \texttt{"Daemon thread running..."} will be
+printed in full before the JVM exits.
+
+\subsection{Real-life use cases of daemon threads}
+
+Daemon threads are ideal for background housekeeping work that should not
+prevent the application from exiting cleanly.
+
+\begin{enumerate}[leftmargin=2em]
+    \item \textbf{Garbage Collection.}
+          The JVM's garbage collector runs as a daemon thread;
+          it must not keep the JVM alive on its own.
+
+    \item \textbf{Log flushing.}
+          A background thread that periodically flushes buffered log entries
+          to disk. If the application finishes, unsaved logs are
+          an acceptable loss compared with hanging the process.
+
+    \item \textbf{Cache invalidation / expiry.}
+          A thread that sweeps an in-memory cache and removes stale entries
+          does not need to outlive the application.
+
+    \item \textbf{Heartbeat / health-check threads.}
+          Service-mesh sidecars and microservices often send periodic
+          pings to a service-discovery system.
+          These should die with the service, not keep it alive.
+
+    \item \textbf{IDE background indexing.}
+          IntelliJ IDEA's indexer and VS Code's language-server workers
+          are typically daemon-like: if you close the IDE, you do not
+          want to wait for them to finish indexing.
+\end{enumerate}
+
+% ════════════════════════════════════════════════════════════════════════════
+\section{A Shorter Way to Create Threads – Lambda Expressions}
+% ════════════════════════════════════════════════════════════════════════════
+
+\begin{lstlisting}[caption={ThreadDemo.java}]
+public class ThreadDemo {
+    public static void main(String[] args) {
+        Thread thread = new Thread(() -> {
+            System.out.println("Thread is running using a lambda!");
+        });
+
+        thread.start();
+    }
+}
+\end{lstlisting}
+
+\subsection{Expected output}
+
+\begin{lstlisting}[language={},numbers=none,backgroundcolor=\color{codebg}]
+Thread is running using a lambda!
+\end{lstlisting}
+
+\subsection{What is \code{() -> \{ \ldots \}} called?}
+
+The \code{() -> \{ \ldots \}} syntax is called a \textbf{lambda expression}
+(also known as an \emph{anonymous function} or \emph{arrow function} in
+other languages).
+
+A lambda expression is a concise way to provide an implementation of a
+\emph{functional interface} – any interface that declares exactly one abstract
+method.
+\code{Runnable} is a functional interface: its single abstract method is
+\code{void run()}.
+The lambda \code{() -> \{ \ldots \}} supplies that implementation inline,
+without naming it.
+
+\subsection{How does this differ from other approaches?}
+
+There are three common ways to supply a \code{Runnable} to a \code{Thread}:
+
+\begin{lstlisting}[caption={Three equivalent approaches}]
+// 1. Class that extends Thread
+class MyThread extends Thread {
+    public void run() { System.out.println("extends Thread"); }
+}
+new MyThread().start();
+
+// 2. Named class that implements Runnable
+class MyRunnable implements Runnable {
+    public void run() { System.out.println("implements Runnable"); }
+}
+new Thread(new MyRunnable()).start();
+
+// 3. Lambda expression (shortest)
+new Thread(() -> System.out.println("lambda")).start();
+\end{lstlisting}
+
+\begin{center}
+\begin{tabular}{>{\bfseries}lllll}
+\toprule
+Approach & Boilerplate & Separate class? & Captures outer vars? & Extensible? \\
+\midrule
+\code{extends Thread}   & High   & Yes (named) & No                & Inherits Thread \\
+\code{implements Runnable} & Medium & Yes (named) & No             & Yes \\
+Anonymous class         & Medium & Yes (anon.) & Yes (eff.\ final) & Yes \\
+Lambda                  & \textbf{Minimal} & No & Yes (eff.\ final) & No \\
+\bottomrule
+\end{tabular}
+\end{center}
+
+\textbf{Key advantages of lambdas:}
+\begin{itemize}[leftmargin=2em]
+    \item \textbf{Conciseness.}
+          No need to declare a class, override a method, or write a constructor.
+          A single line can create and start a thread.
+
+    \item \textbf{Readability.}
+          The intent (``run this block of code in a new thread'') is immediately
+          obvious to the reader.
+
+    \item \textbf{Variable capture.}
+          A lambda can reference local variables from the enclosing scope as long
+          as they are effectively final (i.e., never reassigned after declaration).
+          This is often more convenient than passing data through a constructor.
+
+    \item \textbf{Functional programming patterns.}
+          Lambdas work seamlessly with the Java Streams API, \code{CompletableFuture},
+          \code{ExecutorService}, and other modern concurrency utilities that accept
+          \code{Runnable} or \code{Callable} arguments.
+\end{itemize}
+
+\textbf{Limitation:}
+Because a lambda is not a subclass of \code{Thread}, it cannot override thread
+life-cycle methods such as \code{interrupt()} or \code{setUncaughtExceptionHandler()}
+directly inside the lambda body.
+When that level of control is needed, a named class is more appropriate.
+
+% ── Footer note ──────────────────────────────────────────────────────────────
+\vfill
+\begin{center}
+    \small\color{gray}
+    Advanced Programming – Assignment 8 \quad|\quad
+    Faraz Ardeh \quad|\quad
+    Shahid Beheshti University \quad|\quad
+    June 2026
+\end{center}
+
+\end{document}