1In your own words explain how the Compare and Swap instruct

1.In your own words, explain how the Compare and Swap instruction can prevent more than one process using the shared resource.

2.In your own words, explain how a Semaphore can prevent more than one process using the shared resource.

3.In your own words, explain why the solution on the left is not a correct solution for the consumer/producer problem, but the right one is.

4.Two processes want to use the same shared resource. In your own words, explain how messages can prevent concurrency problems.

int compare-and-swap Cint *value, int expected, int new-value) int temp tok value if value expected) *value new-value; return tempi Figure 5.5 The definition of the compare-and-swap instruction. do while (compare-and-swap (&lock;, 0, 1) 0) do nothing critical section lock 0; remainder section while (true); Figure 5.6 Mutual-exclusion implementation with the compare-and-swap) instruction

Solution

Compare and Swap instruction Uses 1 for locked state and 0 for available .

If a process checks when lock=1 , using the function compare_and_swap , the status does\'nt change and it continues in the locked state .

If a process checks when lock=0 , using the function compare_and_swap , the status changes to lock=1 and a new lock is returned .

This ensures mutual exclusion as a lock is granted only when there is no existing lock . i.e. when lock == expected or from the code when , (*value == expected ) is true i.e. ( 0 == 0 )