Exam 2 COP4610 FSU Wang questions well answered graded A+

Exam 2 COP4610 FSU Wang

Monitor - correct answer ✔✔a lock + condition variables



Lock - correct answer ✔✔provides mutual exclusion to shared data



Condition variable - correct answer ✔✔provides a queue for waiting threads inside a critical section



Hoare vs. Mesa monitors - correct answer ✔✔1.) Hoare Monitors (used in most textbooks)

a.) Signal() transfers the CPU directly to a waiting thread



2.) Mesa Monitors (used in most real operating systems)

a.) Signal() only puts a waiting thread on the scheduler's ready queue

b.) By the time the waken thread gets the CPU, the waiting condition may no longer be true and needs
to be retested



Correct a broken solution - correct answer ✔✔Reader() {

lock.Acquire();

while (activeWriters > 0

|| waitingWriters > 0) {

++waitingReaders;

okToRead.Wait(&lock);

--waitingReaders;

}

++activeReaders;

lock.Release();

// access database

lock.Acquire();

, --activeReaders;

if (activeReaders == 0 &&

waitingWriters > 0) {

okToWrite.Signal(&lock);

}

lock.Release();

}



Writer() {

lock.Acquire();

while (activeWriters > 0

|| activeReaders > 0) {

++waitingWriters;

okToWrite.Wait(&lock);

--waitingWriters;

}

++activeWriters;

lock.Release();

// access database

lock.Acquire();

--activeWriters;

if (waitingWriters > 0) {

okToWrite.Signal(&lock);

} else if (waitingReaders > 0) {

okToRead.Broadcast(&lock);

}

lock.Release();

}