Ch 5 p 227

Question 1

critical section problem

Answer 1

MUST ALLOW EXCLUSIVE ACCESS TO ONE PROCESS

when processes share a lot of variables it serialized the code.

Question 2

Peterson’s solution

Answer 2

int turn; // ready condition
boolean flag[2]; // if process is ready to enter critical seciotn

problem with this solution is that you can only use 1 type of thread

Question 3

use of locks (low level solution)

Answer 3

solution to peterson’s problem

test_and_set // one lock for implementaion
initialize lock to false
if true, set lock to true
if false, set to true (locks processes out)

compare_and_swap // each process has its own lock (new bool value) plus a shared lock (expected)
initialize lock to false
swap if new and expected bool value equal

problem with locks is busy waiting.
solution is sleepy threads ( wait( ) )

Question 4

Mutex locks (high level solution) (spinlock)

Answer 4

acquire() and release() must be atomic

Question 5

Deadlock

Answer 5

when two or more processes are waiting indefinitely for an event that can be cause only by one of the waiting processes

Question 6

race condition

Answer 6

situation where several processes access and manipulate the same data concurrently and the outcome of the execution depends on the particular order in which the access takes place.

Question 7

priority inverison

Answer 7

inverting priority when starvation, or indefinite deadlocks, occur

Question 8

binary semaphore is basically a mutex lock

Answer 8

binary semaphore is basically a mutex lock

Question 9

critical-section solution requirements

Answer 9

mutual exclusion - only one process can execute its critical section
progress - selection can't be postponed indefinitely – no deadlock
bounded waiting (fairness) -  a process requesting to enter its critical section only waits certain time