Chapter 4

Question 1

define thread

Answer 1

basic unit of CPU utilization; comprises a thread ID, PC, register set, and a stack. shares its code section, data section, open files, and signals to other threads

Question 2

what are the 4 benefits of threads

Answer 2

1. responsiveness
2. resource sharing
3. economy
4. scalability

Question 3

define parallelism

Answer 3

performs more than one task simultaneously

Question 4

define concurrency

Answer 4

supports more than one task by allowing all the tasks to make progress, fast switching

Question 5

what is unintuitive about concurrency and parallelism

Answer 5

it is possible to have concurrency without parallelism

Question 6

what are the 5 programming challenges

Answer 6

1. identifying tasks : independent tasks
2. balance : work of equal value
3. data splitting : tasks divided to run on separate cores
4. data dependency: tasks synchronized to accommodate the data dependency
5. testing/debugging

Question 7

what are the two types of parallelism ?

Answer 7

1. data parallelism : distributing same data

2. task parallelism : distributing tasks

Question 8

what are the three multithreading models

Answer 8

1. one-one
2. many-one
3. many-many

Question 9

which multithreading model is the least common and why

Answer 9

many-one. multiple threads are unable to run in parallel

Question 10

which multithreading model runs in parallel

Answer 10

one-one

Question 11

which model doesn’t result in true concurrency

Answer 11

many-many

Question 12

what are the 2 methods for creating/managing threads

Answer 12

1. user space with no kernel support

2. kernel-level library supported directly by OS

Question 13

define thread pools

Answer 13

a solution to unlimited threads exhausting system resources and space

Question 14

what are 3 benefits of thread pools

Answer 14

1. servicing a request within an existing thread is faster than waiting to create a thread
2. thread pool limits # of existing threads
3. separating task to be performed from creating a task

Question 15

what is the flow of pattern of signals

Answer 15

1. signal detected by event occurence
2. signal delivered to process
3. once delivered, signal handled

Question 16

what are the 2 possible signal handlers

Answer 16

1. default signal handler

2. user-defined signal handler

Question 17

what are the 4 options of where a signal should be delivered

Answer 17

1. to which signal applies
2. every thread in process
3. certain thread in process
4. assign a specific thread to receive all signals for the process

Question 18

define thread cancellation

Answer 18

terminating a thread before it has completed

Question 19

what are the 2 scenarios of thread cancellation

Answer 19

1. asynchronous cancellation: immediately terminates target

2. deferred cancellation: target thread terminates itself

Question 20

define lightweight process

Answer 20

TLP, data structure between user and kernel threads of the many-many or 2 level model

Question 21

what are the steps of the scheduler activations

Answer 21

1. kernel provides an application with a set of LWPs

2. application can schedule user threads onto an available virtual processor

Question 22

what is the purpose of the scheduler activation

Answer 22

scheme for communication