ICP

Question 1

What is a Critical Region?

Answer 1

Where processes access shared variables.

Question 2

What are the four criteria for a critical region routine.

Answer 2

1. Mutual exclusion (One at a time)
2. Speed Independent
3. Non-Critical Regions Immaterial
4. Finite Waiting

Question 3

What are the instructions that all process go through?

Answer 3

1. Read
2. Modify
3. Write.

Question 4

describe spin lock

Answer 4

Spin lock is busy waiting on a lock polling.

Question 5

What is Peterson’s Algorithm?

Answer 5

Combines turn taking and “Interested” flags.

Question 6

What are the steps in Peterson’s Algorithm?

Answer 6

1. Raises flag when interested in entering critical region.
2. Gives turn to other process.
3. Checks whether the other process is interested AND it is the other process’ turn, to wait or enter region.
4. When exiting region, lower flag.

Question 7

What is the Test & Set lock (TSL)?

Answer 7

When the process instructions are atomic.

Question 8

What is the meaning of atomic?

Answer 8

Cannot be divided.

Question 9

What IPC mechanism keeps track of the number of available recourses in a count variable?

Answer 9

Semaphore

Question 10

What is considered a binary semaphore, and can only have 0 or 1 as values?

Answer 10

Mutex

Question 11

What are the condition variables for monitors?

Answer 11

• Wait
• Signal

Question 12

What can be true about Readers and Writers?

Answer 12

• Multiple readers can co-exist
• Multiple writers cannot co-exist
• Writers and readers cannot co-exist

Question 13

Reader Priority is when ….

Answer 13

Readers are not kept waiting until a writer gets permission. (Starves writers)

Question 14

Writer Priority is when ….

Answer 14

Readers cannot access if writer is waiting (starves readers)

Question 15

Describe no starvation solution (Mutex solution)

Answer 15

Writers lock the region
-if writer is writing, all incoming readers wait, all go in when writer is done.