Multithreading

Question 1

What is a thread in java?

Answer 1

A thread is a lightweight process that runs within another process or thread. It is an independent path of execution in an application.

Question 2

What is the priority of a thread and how is it used in scheduling?

Answer 2

Every thread has a priority between 1-10. Scheduler uses pre-emptive scheduling so a thread with higher priority gets preference over a lower priority thread.

Question 3

What is the default priority of a thread?

Answer 3

A new thread gets the same priority as the priority of the parent thread. Default priority of a thread is 5.

Question 4

What are the different priorities that can be set?

Answer 4

MIN_PRIORITY: 1
NORM_PRIORITY: 5
MAX_PRIORITY: 10

Question 5

What is the purpose of the join() method in java?

Answer 5

We can use the join() method on a thread to make current thread wait for another thread to finish. When we use join(), the current thread stops executing. It waits for the thread on which join() was called to finish.

Question 6

What is the difference between wait() and sleep()?

Answer 6

When we call wait() the current threaded releases the monitor and goes into a waiting state. Then another thread calls notify() to wake it up.
When we call sleep() the current thread just sleeps for some pre defined period of time.

Question 7

What are the advantages of multithreading?

Answer 7

Improved performance, simultaneous access to multiple applications, reduced number of servers required, simplified coding.

Question 8

What are the disadvantages of multithreading?

Answer 8

Difficult to debug, difficult to manage concurrency, difficult to port existing code into multithreaded code, deadlocks.

Question 9

Can you lock an object for exclusive use by a thread?

Answer 9

Yes, using a synchronised block we can lock an object to a specific thread.

Question 10

Difference between notify() and notifyAll()?

Answer 10

Notify is used to unblock a specific thread that is in waiting state. NotifyAll is used to unblock all waiting threads.

Question 11

What is a daemon thread in java?

Answer 11

A low priority thread that does not prevent the JVM from exiting when the program finishes. Garbage collection is an example of a daemon thread.

Question 12

What is synchronisation?

Answer 12

It is a feature in Java that helps in controlling the access of multiple threads to a shared resource.

Question 13

What is the purpose of Synchronised block in java?

Answer 13

It can prevent thread interference, it is used to avoid memory inconsistency issues.

Question 14

What is a deadlock?

Answer 14

A deadlock is a situation in which two or more threads are waiting on each other to release a resource. This can result in a universal waiting state.

Question 15

What is the meaning of concurrency?

Answer 15

The ability of a program to execute several programs simultaneously. This is achieved by distributing computation over multiple CPU cores of a machine or over different machines within the same network.

Question 16

Difference between a process and a thread?

Answer 16

A thread runs in a shared memory space, a process runs in its own space. A process runs in an environment provided by the operating system. A thread lives within a process and shares the resource like-memory.

Question 17

What is a scheduler?

Answer 17

A program that is the implementation of a scheduling algorithm to manage access of processes and threads to limited resources like CPU or I/O channel. The goal is to provide load balancing for the available processes/threads.

Question 18

What are the different states of a thread?

Answer 18

New: new thread created
Runnable: a thread executing in the JVM is in Runnable state
Blocked: a thread waiting for a monitor lock is in a blocked state
Waiting: a thread in a waiting state
Terminated: a thread that has exited

Question 19

How to create a thread?

Answer 19

Extend thread class: we can extend thread class and implement the run() method.
Implement runnable interface: we can implement runnable interface and pass the implemented object to the constructor of the thread class.

Question 20

What is an atomic operation?

Answer 20

An operation that completes in a single step relative to other threads. It is either executed completely or not at all.

Question 21

What is thread starvation?

Answer 21

Threads with lower priority get less time for execution than higher priority threads. Thread starvation occurs when a lower priority thread does not get enough time to finish computation.

Question 22

What is a race condition?

Answer 22

When a program attempts to perform two or more operations at the same time, but because of the logic of the program, the operations have to be performed in proper sequence to run the program correctly.