Lecture 4 (unfinished)

Question 1

What is Resource Ownership in terms of Processes?

Answer 1

Process includes a virtual address space to hold the process image
• The OS performs a protection function to prevent unwanted interference between processes with respect to resources

Question 2

What is Scheduling/Execution in terms of Processes?

Answer 2

Follows an execution path that may be interleaved with other processes
 A process has an execution state (Running, Ready, etc.) and a dispatching priority, and is the entity that is scheduled and dispatched by the OS

Question 3

What is a Thread (Lightweight process)?

Answer 3

The unit of dispatching is referred to as a thread

Question 4

What is a process (task)?

Answer 4

Defined in a multithreaded environment as “the
unit of resource allocation and a unit of protection”

Associated with processes:
A virtual address space that holds the process image
Protected access to:
 Processors
 Other processes (for interprocess communication)
 Files
 I/O resources (devices and channels)

Question 5

What is multithreading?

Answer 5

Multithreading - The ability of an OS to support multiple, concurrent paths of execution within a single process.

Question 6

Check multithread and single thread model/pics slide 5

Answer 6

Check multithread and single thread model/pics slide 5

Question 7

What does each thread have ?

Answer 7

Access to the memory and resources of its processes, shared with all other threads in that process

 An execution state (Running, Ready, etc.)
 A saved thread context when not running
 An execution stack
 Some per-thread static storage for local variables

Question 8

2 benefits of threads?

Answer 8

Takes less time to create a new thread than a process

Less time to terminate a thread than a process

Question 9

What is Thread Use in a Single-User System?

Answer 9

Foreground and background work in parallel
•Asynchronous processing
•Speed of execution
•Modular program structure

Question 10

What is suspending a process?

Answer 10

 Suspending a process involves suspending all threads of the process

Question 11

What is a termination of a process?

Answer 11

Termination of a process terminates all threads within the process

Question 12

What is thread syncronization?

Answer 12

It is necessary to synchronize the activities of the various threads
•All threads of a process share the same address space and other resources
•Any alteration of a resource by one thread affects the other threads in the same process

Question 13

What are the 2 types of threads?

Answer 13

User Level thread

Kernel Level thread

Question 14

What is a user Level Thread (ULT)?

Answer 14

• All thread management is done by the application

* The kernel is not aware of the existence of threads

Question 15

2 advantages of ULT?

Answer 15

Thread switching does not require kernel mode privileges

ULTs can run on any OS

Question 16

1 Disadvantage of ULT?

Answer 16

Many system calls are blocking

When a ULT executes a system call, the thread and all of the threads within the process are blocked

Question 17

What is a kernel level thread?

Answer 17

Thread management is done by the kernel

No thread management code in the application level, simply an application programming interface (API) to the kernel thread facility

Question 18

Advantage of kernel level thread?

Answer 18

The kernel can simultaneously schedule multiple threads from the same process on multiple processors

Question 19

Disadvantage of kernel Level thread?

Answer 19

The transfer of control from one thread to another within the same process requires a mode switch to the kernel