Multithreading

Question 1

what does a thread comprise of

Answer 1

id, counter, register and stack

Question 2

Threads within a process share what

Answer 2

code, data+files, signals etc

Question 3

User threads

Answer 3

supported above the kernel and managed without kernel support, primarily by user-level threads library

Question 4

Kernel threads

Answer 4

supported and managed directly by the OS

Question 5

many to one mapping

Answer 5

many user threads to one kernel thread
Pure used level thread implementation
If one thread blocks then all block

Question 6

one-to-one mapping

Answer 6

creating a user level thread creates a kernel thread - more concurrency no. threads per process is usually restricted

Question 7

Many to many mapping

Answer 7

many user level threads to be mapped to equal no. or smaller no. of kernel threads
Allows OS to create a sufficient number of kernel threads.

Question 8

PThreads

Answer 8

Threads that may either be provided as user-level or kernel level threads
Specifications not implementations
POSIX standard API thread creation and synchronization

Question 9

Implicit threading

Answer 9

creating and management of threads are done by a compiler

- create tasks that gets mapped onto a framework -e.g. java fork() join()

Question 10

Name and explain the 2 approaches to thread cancellation

Answer 10

Asynch - terminates thread immediately
Deferred - allows target thread to periodically check if it should be cancelled, allows the thread to terminate in an orderly fashion.

Question 11

Why could asynchronous cancellation of threads be dangerous

Answer 11

when resources allocated to a cancelled thread are either not released or are in an unsafe state