Classical synchronization problems

Question 1

Producer threads

Answer 1

create items of some kind and add them to DS

Question 2

consumer threads

Answer 2

remove and process items

Question 3

Example of producer consumer relationships

Answer 3

event driven programs

• when event occurs, the prod thread creates an event object and adds it to the event buffer
• consumer threads take events out of buffer and process them - concurrently

Question 4

What is the producer consumer problem?

Answer 4

while being added or removed the buffer is in an inconsistent state. threads therefore need to have exclusive access to buffer
- consumer arrives while buffer is empty, it needs to block until a producer adds a new item

• bounded buffer variant, producer cannot produce if buffer is full

Question 5

Synchronization constraints for readers-writers problem

Answer 5

any number of readers can be in the critical section simultaneously
writers need exclusive access to their critical section

Question 6

Two types (variations) of how readers and writers are considered

Answer 6

1. no reader is kept waiting unless writer has permission to use shared object - prioritizes readers
2. once reader is ready it performs the write ASAP

Question 7

Liveness

Answer 7

processes must make progress and not wait indefinitely

Question 8

Starvation

Answer 8

indefinite blocking e.g. process never removed from semaphore queue

Question 9

Deadlock

Answer 9

two or more processes are waiting infinitely long for an event that can never occur