Threads

Question 1

Concurrency

Answer 1

Managing multiple tasks at the same time, but not necessarily doing them literally at the same instant

Question 2

Parallelism

Answer 2

Doing multiple things at the exact same time, using multiple CPU cores

Question 3

Can an application be concurrent but not parallel?

Answer 3

Yes e.g. multitasking on a single-core CPU

Question 4

What is a thread?

Answer 4

A mini-program running inside a main program. Programs can have multiple threads doing tasks at the same time

Question 5

Why use multithreading?

Answer 5

• Responsiveness: Avoid blocking
• Resource Sharing: Threads share memory by default
• Economy: Faster to create/switch than processes
• Scalability: Utilises multiple cores effectively

Question 6

What are the states of a Java thread?

Answer 6

• NEW: Created but not started
• RUNNABLE: Ready or running (scheduler decides)
• BLOCKED: Waiting for a monitor lock
• WAITING: Indefinite wait
• TIMED_WAITING: Waits with timeout
• TERMINATED: Completed execution

Question 7

What is Amdahl’s Law?

Answer 7

Speedup <= 1/ S+[(1-S)/N], S=serial portion, N=cores. Limits speedup due to serial code

Question 8

Name multicore programming challenges

Answer 8

Load balancing, Data dependencies/synchronisation, debugging parallel tasks

Question 9

Why use multithreading in servers?

Answer 9

• Single-threaded: Poor responsiveness (one client at a time)
• Process-per-request: Heavy overhead
• Multithreaded: Efficiently handle multiple requests (one thread per request)

Question 10

Creating Threads in Java, Method 1: Extend Thread class

Answer 10

class MyTask extends Thread {
public void run() {
System.out.println(“Task is running!”);
}
}
public class Main {
public static void main(String[] args) {
MyTask t = new MyTask();
t.start();
}
}

Question 11

Creating Threads in Java, Method 2: Implement Runnable

Answer 11

class MyTask implements Runnable {
public void run() {
System.out.println(“Task is running”);
}
}
public class Main {
public static void main(String[] args) {
Threads t = new Thread(new MyTask());
t.start();
}
}