CS2005 - Lecture 10 - Threads

Question 1

What is a thread in the context of process management?

Answer 1

A thread is the basic unit of CPU utilization; It includes a thread ID, program counter, register set, and stack; Threads share code, data, and OS resources with other threads of the same process

Question 2

What is the main benefit of using threads in applications?

Answer 2

Threads enable simultaneous execution of tasks, improving responsiveness and CPU utilization; They are lightweight and more economical than creating new processes

Question 3

What are the differences between concurrency and parallelism?

Answer 3

Concurrency: Tasks appear to run in parallel through time-slicing; not necessarily at the same time; Parallelism: Tasks actually run at the same time on multiple processors or cores

Question 4

How does sequential execution differ from concurrent and parallel execution?

Answer 4

Sequential: One task executes at a time, others must wait; Concurrent: Multiple tasks are interleaved in execution; Parallel: Multiple tasks execute simultaneously on separate CPUs/cores

Question 5

What is the lifecycle of a Java thread?

Answer 5

NEW → RUNNABLE → RUNNING → may go to WAITING, TIMED_WAITING, BLOCKED, or TERMINATED

Question 6

What happens when a thread enters the WAITING state?

Answer 6

It waits indefinitely for another thread to perform an action (e.g., wait() called)

Question 7

What is Amdahl’s Law and how does it relate to multicore performance?

Answer 7

Amdahl’s Law estimates the potential speedup of a program using multiple cores; Formula: speedup ≤ 1 / (S + (1 - S)/N) where S = serial fraction, N = number of cores

Question 8

What are the advantages of multithreaded server architecture?

Answer 8

Efficient handling of multiple client requests using threads instead of processes; Lower overhead and quicker context switching

Question 9

How can threads be created in Java?

Answer 9

By extending the Thread class and overriding run(); By implementing the Runnable interface

Question 10

Why is multithreading beneficial in multicore systems?

Answer 10

It allows actual parallel execution of threads, improving performance and scalability

Question 11

What does the RUNNABLE state mean in Java thread lifecycle?

Answer 11

The thread is ready to run and waiting for CPU time from the thread scheduler

Question 12

What are the key benefits of threads over processes?

Answer 12

Faster creation and context switching; Shared memory space; Improved responsiveness; Better scalability on multicore systems

Question 13

How does Java put a thread into TIMED_WAITING state?

Answer 13

Using methods like sleep(millis) or wait(millis)

Question 14

What is the difference between BLOCKED and WAITING states in Java?

Answer 14

BLOCKED: Waiting for a lock; WAITING: Waiting indefinitely for an event or action

Question 15

What are common use cases for threads in desktop applications?

Answer 15

UI responsiveness (e.g., UI thread + background threads); Networking (e.g., downloading while rendering UI); Parallel computations

Question 16

What methods are commonly used to control thread behavior in Java?

Answer 16

start(), run(), sleep(), wait(), notify(), interrupt()

Question 17

What happens when a thread finishes execution?

Answer 17

It transitions to the TERMINATED state

Question 18

Why is thread creation more efficient than process creation?

Answer 18

Thread creation uses shared memory and resources of the process, avoiding expensive memory allocation and setup steps

Question 19

In what scenario would concurrency not result in performance gain?

Answer 19

On single-core systems where tasks are context-switched rather than executed in parallel; overhead may even reduce performance

Question 20

Why is synchronization important in concurrent and parallel systems?

Answer 20

To prevent race conditions, ensure data integrity, and avoid deadlocks when multiple threads access shared data

Question 21

What are some risks or drawbacks of using multithreading?

Answer 21

Deadlocks, race conditions, difficult debugging, increased complexity, and nondeterministic behavior

Question 22

Compare RUNNABLE vs. RUNNING in Java threads.

Answer 22

RUNNABLE: Eligible to run but waiting for CPU; RUNNING: Currently executing on a CPU

Question 23

Describe an application that benefits from both concurrency and parallelism.

Answer 23

A video game: concurrent threads for input, rendering, and audio; parallel execution on multicore systems improves performance

Question 24

How does multithreading improve responsiveness in GUI applications?

Answer 24

Background threads handle long-running tasks (e.g., file download), allowing the UI thread to stay interactive

Question 25

When would you prefer implementing Runnable over extending Thread?

Answer 25

When you need to inherit from another class (Java doesn't support multiple inheritance), or want to decouple task logic from threading

Question 26

What happens if you call run() directly instead of start() on a thread?

Answer 26

It will execute like a normal method call in the current thread, not in a separate thread

Question 27

How does Java handle thread scheduling?

Answer 27

It's managed by the JVM and OS; generally based on thread priority and time-slicing