5 - Process Comms and Deadlock

Question 1

What is the Critical Section Problem?

Answer 1

processes all competing for the same shared data

Ensure that when one process is executing in its critical section, no other process is allowed to execute in its critical section

Question 2

Necessary elements of a critical section solution

Answer 2

Mutual Exclusion
-at most one process can be in its critical section at any time

Progress
- all processes should eventually be permitted to do so

Fairness
- Scheduling needs to be fair (bounded waiting)

Question 3

What is the producer consumer problem?

Answer 3

A producer process produces info that is consumed by a consumer process

Question 4

Circular Array

Answer 4

buffer can be org as a circular array with in/out pointers:

• in: next free position in buffer
• out: first full pos in buffer

Question 5

What is a “race condition”?

Answer 5

A situation where the order of execution affects data

Question 6

Semaphore

Answer 6

An integer variable only modified by p and v operations

Question 7

p operation

Answer 7

test a lock
enter if free
secure lock

or wait for lock to be free

Question 8

v operation

Answer 8

free the lock

Question 9

Deadlock

Answer 9

• When two processes wait for a resource held by another but that it cannot give up due to it waiting for another resource