Threads

Question 1

How does single core systems have multiple threads?

Answer 1

Time-Slicing.

Question 2

What is a thread?

Answer 2

A lightweight process. A process is used for heavyweight tasks like executing an application. Threads exist in a process. Threads share process resources.

Question 3

What is multi-threading?

Answer 3

Example: word prints docmnent but also accepts user input typing.

Question 4

What are critical sections?

Answer 4

Code that modifies data structures shared by multiple threads.

Question 5

What is synchronization?

Answer 5

When code of one thread is in critical section it’s important another thread isn’t allowed in critical section. Signaled and unsignalled.

Question 6

In Java, how to start a thread?

Answer 6

Provide runnable object (implements Runnable). Must have run() method. Runnable object then passed to Thread constructor. Must also invoke Thread.start().

Question 7

How do you make thread sleep?

Answer 7

Thread.sleep(msec);

Question 8

What is an interrupt? How is interrupt done?

Answer 8

A thread should stop what it’s doing and do something else. Use try catch for interrupted exception and return out of catch block.

Question 9

How do you get name of current thread?

Answer 9

Thread.currentThread().getName();

Question 10

How do you check if a thread is alive?

Answer 10

t.isAlive() - it returns a Boolean

Question 11

How to wait for thread t? How to interrupt thread t?

Answer 11

t. join(msec);

t. interrupt();

Question 12

What is thread contention?

Answer 12

When two or threads try to access the same resource simultaneously and as a result they execute more slowly or not at all.

Question 13

How to make a method synchronized?

Answer 13

public synchronized void increment(){}

Question 14

Write a synchronized statement:

Answer 14

synchronized (this){}

Question 15

What is deadlock?

Answer 15

Two or more threads blocked forever, waiting for each other.

Question 16

What is starvation.

Answer 16

Other greedy threads make resources unavailable for a thread.

Question 17

What is livelock?

Answer 17

Two threads unable to make progress as they keep responding to each other’s responses. Like two people meeting in corridor.

Question 18

What are guarded blocks? ie using wait() method?

Answer 18

while(!someCondition){
try { wait(); }
catch (InterruptedException e) {}
}} print }

wait() does not return until another thread issues notification that some event has occurred.

Question 19

How does another thread let other threads know it has squired look and some important event has happened?

Answer 19

notifyAll();