4 - Threads

Question 1

Define Threading:

Answer 1

Multiple threads of execution within a single process.

Question 2

Is forking a process efficient? If not, why?

Answer 2

No, because it copies everything.

Question 3

Define a Thread:

Answer 3

A tread is a basic unit of CPU utilization.

Question 4

Do Threads of a process have their own separate memory or share memory together?

Answer 4

Threads of a process share memory but can execute independently.

Question 5

In Web Servers, why is Forking inefficient compared to threading other than because it copies everything?

Answer 5

Web serveres have caches for read pages - forking means that these caches cannot be shared. Threads allow for these caches to be shared.

Question 6

What do threads share?

Answer 6

• Process Address space (text, data, heap)

- OS State (open files, sockets, locks)

Question 7

What do threads not share?

Answer 7

They have their own CPU context:

- Program counter, Stack pointer, register state, stacks

Question 8

Give 4 benefits of threads:

Answer 8

Responsiveness
Resource Sharing
Allocating memory and resources for process creation is costly which is avoided.
Context-switching is faster

Question 9

What does a thread library provide for the programmer?

Answer 9

An API for creating and managing threads

Question 10

What are the 3 main libraries?

Answer 10

1) POSIX Pthreads
2) Win32
3) Java

Question 11

True or false: Threads also share global variables which is a another pros.

Answer 11

False; sharing global variables is dangerous