Concurrent Processes

Question 1

What are concurrent processes ?

Answer 1

Processes that can share physical or logical recourses.

Question 2

What are the problems with concurrent processes ?

Answer 2

Race conditions: Two processes accessing/ modifying shared data simulatneously causes inconsistent or lost results.
Critical Region: Section of code where shared recources are accessed (only one process should execute this at time).

Question 3

What is required to help prevent issues ?

Answer 3

Mutual exclusion (mutex).

Question 4

What is the main Software-Based Mutex ?

Answer 4

Peterson’s Algorithm -
Uses flags and a turn a variable to ensure only one processes enters its critical region at a time,
Prevents race conditions but leads to busy waiting.

Question 5

What is the main Hardware-Based Mutex ?

Answer 5

Test-and-set Instruction -
Performs test and assignement atomically (no intervention),
Solves the race condtition but still causes CPU time wastage due to busy waiting.

Question 6

What is a Semaphore ?

Answer 6

A protected integer variable used to control access,
Binary semaphore (0 or 1)
Counting semaphore (> 0)

Question 7

What are the two atomic operations of semaphores ?

Answer 7

wait() - decrements the semaphore; blocks if <= 0,
signal() - increments and potentially unblocks a waiting process.

Question 8

How do we handle multiple producers and consumers ?

Answer 8

Scaling the semaphore logic to allow the multiple producers and consumers to access the buffer concurrently.