[作業] Operating_System_Homework6

[Asbarla (木頭)]

6-1.

The first known correct software solution to the critical-section problem

for two processes was developed by Derek Fisher. The two process, P0 and P1

,shared the following variables:


        boolean flag[2];                /*initially fales */

        int turn;

        do {
            flag[i] = TRUE;

            while(flag[j]) {

            if(turn == j) {

                flag[i] = false;

                while(turn == j)

                ;//do nothing

                flag[i] = TRUE;
            }
        }
            // critical section

        turn = j;

        flag[i] = FALSE;

           // remainder section

      } while(TRUE);

The structure of precess Pi (i == 0 or 1) ;

The other process is     Pj (j == 1 or 0) ;

Prove that the algorithm

satisfies all three requirements for the critical-section problem.


6-2.

Explain why interrupts are not appropriate for implementing synchronization

primitives in multiprocessor systems.


6-11.

Show that, if the wait() and signal() semphore operations are not executed

atomically, then mutual exclusion may be violated.


6-21.

Explain why spinlocks are not appropriate for single-processor systems yet

are often used in multiprocessor systems.


6-28.

What is the meaning of the term busy waiting? What other kinds of waiting are

there in an operating system? Can busy waiting be avoided altogether?

Explain your answer.

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