Algorithm Concurrency - Lock Variables

Question 1

Lock

Answer 1

A shared data item

Processes must acquire such a lock before entering a critical section

Processes have to release a lock when exiting critical section

Question 2

Synonym for the Lock Variables

Answer 2

Mutex

Question 3

Syntax

Answer 3

process ()
{
acquire lock
critical_section() ;
release lock
remainder_section();
}

Question 4

True vs False Lock

Answer 4

True - Critical Section Locked
False - Critical Section Unlocked

Question 5

while(lock == TRUE) {
// wait
}

Answer 5

This is a loop that keeps the process waiting (doing nothing) until the lock variable becomes FALSE

this while loop continuously checks the lock condition, as long as the condition is true (meaning the shared resource is being accessed by another process) the loop doesn’t allow the process to move forward.It stays stuck in the loop effectively waiting

once the lock variable is set to false (by the other process releasing the resource) the condition lock == TRUE becomes FALSE

Question 6

Issues with Lock variable

Answer 6

As the process continuously evaluates whether a lock has become available

Question 7

Token - Shared variable

Answer 7

Usually process ID

Indicated which process is next to enter critical section, set by previous process

Question 8

p0
while(TRUE) {

while(turn !=0) {
//wait
}

critical_section
turn= 1
non critical section

Answer 8

turn is a shared variable

turn=0 means P0 has the right to execute the critical section
turn=1 means P1 has the right to execute the critical section

each process alternates between the critical and non-critical section

P0 waits in the loop until turn==0 which means it is P0 to execute the critical section

once the critical section completed the process changes the turn variable to the next number to allow P1 to proceed to the critical section too