Chapter 4 Threads

Question 1

What happens when a user level thread ULT blocks in a multithreaded process that is mapped to only one kernel level thread?

Answer 1

The process stops.

Question 2

List one advantage of having a thread pool.

Answer 2

Faster to service a request with a existing thread.

Question 3

What is a LWP?

Answer 3

(Light Weight Process), maps user level to kernel level thread to one or more user level thread.

Question 4

Do threads have their own stack pointer?

Answer 4

yes

Question 5

Why does it take less time to create a user level thread as opposed too a kernel level thread?

Answer 5

user level thread does not involve kernel, kernel level threads create overhead.

Question 6

What are the benefits of multithreaded programming?

Answer 6

Responsiveness, Resource sharing, Economy, Utilization of MP Architectures

Question 7

What are some examples of how threads are used?

Answer 7

File Server, Spread Sheet Program and Word Processor

Question 8

What’s Solaris’ purpose? Describe some concepts

Answer 8

Implements the one-to-one mapping from LWP to a kernel thread and a one or more mapping between User-level thread.

Process – normal UNIX process
User-level threads – allows application parallelism
Lightweight processes
Kernel threads – entities manipulated by the scheduler

Question 9

What are the advantages and disadvantages of user-level threads?

Answer 9

Advantages: Portable, scheduling is dependent on application needs, doesn’t require kernel mode intervention when switching threads.

Disadvantages: All threads are blocked when a system function is called

Question 10

What’s the significance of User level threads?

Answer 10

Thread management, they…….
Create and destroy threads
Communication between threads
Scheduling and saving and restoring thread contexts

Libraries include:
Win32
POSIX Pthreads
java

Question 11

What’s the advantage and disadvantages of kernel level threads?

Answer 11

Advantage: Supported by the Kernel

Major disadvantage – switching between threads requires a mode switch to the kernel

Examples:
Windows XP/2000
Solaris
Linux
Tru64 UNIX
Mac OS X

Question 12

Many to one

Answer 12

maps many user-level threads to one kernel thread.

Entire process blocks when a blocking system call is invoked.

Because of one kernel thread mapping, other threads can not run in parallel on a multiprocessor.

Examples:
Solaris Green Threads
GNU Portable Threads

Question 13

One-to-One

Answer 13

maps each user thread to a kernel thread.

allows multiple threads to run in parallel on multiprocessors.

Examples:
Windows NT/XP/2000
Linux
Solaris 9 and later

Question 14

Many-to-Many

Answer 14

Allows many user level threads to be mapped to many kernel threads.

Allows the operating system to create a sufficient number of kernel threads.

Question 15

Data parallelism

Answer 15

Focuses on distributing subsets of the same data across multiple computing cores and performing the same operation on each core.

Question 16

Task parallelism

Answer 16

Involves distributing not data but tasks (threads) across multiple computing cores.

Question 17

What’s the difference between a thread and process?

Answer 17

A thread is a basic unit of CPU utilization. A process is an executing program.

Question 18

How do Solaris kernel threads communicate to the application.

Answer 18

With light weight process.