Concurrency Control

Question 1

what is the bounded-buffer problem (producer-consumer)

Answer 1

a process produces data, another consumes it, and their rates may vary. they share a buffer. to solve this we synchronise when the buffer is empty or full

Question 2

what is a race condition?

Answer 2

a situation in which two processes or threads are trying to acquire the same resource, and the order of access is relevant

Question 3

what is a critical section?

Answer 3

a process is in a critical section when it is accessing shared data. we need to ensure that only one process can be executing in a critical section at a given time, to avoid race conditions. the entry and exit from the section must be atomic

Question 4

what is a spin lock/busy wait?

Answer 4

a while loop that loops while the lock is on, and then breaks when the lock is unlocked

Question 5

what are the semaphore operations?

Answer 5

wait
delays until the sem is > 0 then decrements it
and signal
increments the sem

Question 6

what is a monitor?

Answer 6

a high level tool that provides syncronised operations
a process takes a monitor and then other processes cant run with that monitor
contains a queue of suspended processes
can contain condition variables that support variable-level exclusivity, x.wait() e.g.

Question 7

what are the conditions for a deadlock?

Answer 7

• mutual exclusion (at least 1 resource is not shareable)
• hold and wait (process holds a resource and is waiting for another)
• no resource preemption
• circular wait (processes are waiting in a loop)

Question 8

what are some deadlock strategies?

Answer 8

prevention - make sure they’re impossible. processes can declare their maximum needs and we can schedule accordingly.
recovery - detect it and correct it
ignore it - most common