Mod 1: Thread properties

Question 1

What is a thread?

Answer 1

(1) A single sequential flow of control within a program
(2) Sequence of instruction
(3) A unit of work that can be executed

Question 2

What does a thread share with the process and what does it has its own of?

Answer 2

It do share

(1) same memory space
(2) same program code and global data

but has its own

(1) set of registers
(2) stack

Question 3

Why is using single-threaded applications on modern computers underuse the capacity of of the computer?

Answer 3

Because modern computer often have multiple cores serving as mini-CPU. Using a single-threaded application loads one core with a lot of work, while the other cores stay idle.

Question 4

What are the four typical states that a thread can have?

Answer 4

(1) Ready
(2) Running/Active
(3) Blocked/Waiting
(4) Terminated

Question 5

What does a “ready” thread mean?

Answer 5

Created, but not started

Question 6

What can cause a thread to die?

Answer 6

• It is done with its task
• Exception or other unusual event

Question 7

When does thread blocking occur?

Answer 7

When a thread is unable to continue its execution because it is waiting for something

Question 8

Give example for what thread could be “waiting” on

Answer 8

(1) Resources to become available
(2) Conditions to be true
(3) Event to occur

Question 9

What happens when a thread is blocked?

Answer 9

It becomes temporarily suspended and other threads are allowed to execute

Question 10

How can a blocked thread resume its work?

Answer 10

By receiving CPU-time again

Question 11

What is “sleep”?

Answer 11

Timed waiting

Question 12

Why would we want to put a thread in sleep-mode?

Answer 12

to make processor time available for other threads

Question 13

What happens if there is no CPU time when the sleep time is over?

Answer 13

Nothing, the thread in sleeping-state need to receive CPU-time before resuming its task

Question 14

What is the difference between a foreground thread and a background thread?

Answer 14

a foreground thread keep the application alive and the background thread is running “behind the scenes”, this mean that if the foreground thread is terminated and we exit the application, the background thread will die regardless of if they are done with their tasks

Question 15

What is a foreground thread?

Answer 15

The thread keeping the application alive, JVM cannot exit the application when there is a foreground thread running

Question 16

Explain why multithreaded programs are non-deterministic

Answer 16

Becauses every thread has its own path of execution and we cannot controll the flow of execution. The output can be different every time we run, despite the same input.

Question 17

Will a thread automatically start upon creation?

Answer 17

No, the thread has to be started after being created

Question 18

What is a “join”-method?

Answer 18

Join is a synchronization method that blocks the calling thread (that is, the thread that calls the method) until the thread whose Join method is called has completed

Question 19

Why is “join”-method used?

Answer 19

Join is used when we want one thread to wait for the completion of another thread

Question 20

How does the “join”-method work if we want one thread to wait for completion of another thread?

Answer 20

The join method of a thread is used to let the caller method wait until the threads whose join method is called is terminated.

Question 21

When is the first and only mandatory thread creating?

Answer 21

at run-time, its job is to keep the application running