Chapter 4 (Threads)

Question 1

What are the two main characteristics of a process?

Answer 1

Resource ownership

Scheduling/execution

Question 2

T/F A processes main characteristics could be split apart and managed separately

Answer 2

T

Question 3

What do we get if we split the two main characteristics of a process?

Answer 3

Process: owns resources

Thread: Executes

Question 4

Refers to multiple threads of execution in a single process

Answer 4

Multithreading

Question 5

What is a process called that is not multithreaded?

Answer 5

Single-threaded

Question 6

How many threads does MS-DOS support?

Answer 6

1

Question 7

T/F Traditional UNIX supports multiple user processes but only supports one thread per process

Answer 7

T

Question 8

What modern OS’s support multiple threads per process?

Answer 8

Solaris and Windows

Question 9

What does a process have in a multithreading context?

Answer 9

Virtual address space for the process image

Resource ownership

Question 10

What does a thread have in a multithreading context?

Answer 10

Thread execution state

Thread context

Stack

Local variables

Shared access to memory and resources of its process

Question 11

T/F In a multithreaded process model, each thread shares the user stack and kernel stack

Answer 11

F, they each have their own

Question 12

What are some benefits of threads?

Answer 12

Faster to create

Faster to terminate

Faster to switch between

Communication between threads is more efficient

Question 13

T/F Threads make program organization harder

Answer 13

F, they can make it easier

Question 14

“word processor, thread to periodically save to disk” is an example of:

Answer 14

Asynchronous processing

Question 15

overlapping activity is an example of:

Answer 15

Speed-up execution

Question 16

Structuring a program logically into threads may aid with program design” is an example of:

Answer 16

Modularity

Question 17

What states are associated with a thread?

Answer 17

Running

Ready

Blocked

Question 18

T/F Suspending a process involves suspending all threads of the process since all threads share the same address space

Answer 18

T

Question 19

T/F Termination of a process would terminate all threads within the process

Answer 19

T

Question 20

What is a key benefit of threads?

Answer 20

Speed-up in execution through parallelism

Question 21

T/F On a uniprocessor with multithreading, threads among the same process or differing processes are interleaved

Answer 21

T

Question 22

What are the two ways to implement thread support in an OS?

Answer 22

User-level threads

Kernel-level threads

Question 23

What are user-level threads?

Answer 23

Supports threading with the use of a thread library and the OS is not aware of the threads

Question 24

What are kernel-level threads?

Answer 24

The OS supports threads itself

Question 25

What are the advantages of user-level threads?

Answer 25

Thread switching does not involve the kernel (so it’s faster)

Scheduling can be application specific

Can run on any OS

Question 26

What are the disadvantages of user-level threads?

Answer 26

Most system calls are blocking for processes (all threads within the process will be blocked)

The kernel can only assign processes to processors (two threads within the same process cannot run simultaneously on two processors)

Question 27

What are the advantages of kernel-level threads?

Answer 27

The kernel can simultaneously schedule many threads of the same process on many processors

Blocking is done on a thread level, so one thread in a process can block while another runs

Kernel routines can be multithreaded

Question 28

What are the disadvantages of the kernel level threads?

Answer 28

Thread switching within the same process requires a mode switch to the kernel, which may result in a significant slowdown

Question 29

Amdahl’s law formula

Answer 29

1/(1-f)+(f/N)

Question 30

T/F Typically, there is the same overhead cost as the number of processors involved increases

Answer 30

F, increased overhead

Question 31

Can be made to run effectively on a multicore system

Answer 31

Database servers

Question 32

What are some other examples of software that may benefit with multiple cores?

Answer 32

Multithreaded applications

Multiprocess applications

Java applications (JVM as well)

Multi-instance applications (running more than one instance in parallel)