process

Question 1

What’s Mutual Exclusion?

Answer 1

If process P1 is executing in its critical section then no other processes can be executing in their critical sections

Question 2

Progress?

Answer 2

If no processes are in their critical section and other processes wish to enter their critical section then the processes that are queued to enter can not be postponed

Question 3

What is Bounded Waiting?

Answer 3

A bound must exist on the number of times that other processes are allowed to enter their critical sections after a process has made a request to enter its critical section before that request is granted.

Question 4

What is Preemptive?

Answer 4

Allows preemption of process when running in kernel mode

Question 5

What is Non Preemptive?

Answer 5

Runs until exits kernel mode, blocks or voluntarily yields CPU. Essentially free of race conditions in kernel mode

Question 6

What is Bounded Buffer Problem?

Answer 6

• Buffers can only hold one item each
• semaphore mutex initialized to 1
• semaphore full intialized to 0
• semaphore empty initialized to the value n

Question 7

What is the Readers Writers Problem?

Answer 7

• A data set is shared among a number of concurrent processes
• Readers: can only read that data set. they dont perform any updates
• Writers: Can bot read and write

Problem: Allow multiple readers to read at the same time. Only one single writer can access the shared data at the same time

Question 8

Variations?

Answer 8

• First Variation: No reader kept waiting unless writer has permission to use shared object
• Second Variation: Once writer is ready, it performs the write asap
• Both may have starvation leading to even more variations
• Problem is solved on some systems by kernel providing reader writer locks

Question 9

What is a Counting Semaphore?

Answer 9

• Integer value can range over an unrestricted domain

Question 10

What is a Binary Semaphore?

Answer 10

• Integer value can range between only 0 and 1. same as a mutex lock

Question 11

Semaphore Implementation with no busy waiting

Answer 11

• Block : place the process invoking the operation on the appropriate waiting queue
• Wakeup: remove one of the processes in the waiting queue and place it in the ready queue

Question 12

What is a deadlock?

Answer 12

Two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting processes

Question 13

Starvation - Indefinite blocking

Answer 13

• A process may never be removed from the semaphore queue when it is suspended

Question 14

Priority Inversion

Answer 14

• Scheduling problem when lower- priority process holds a lock needed by higher priority process
• Solved via priority inheritance protocall