Quiz 3

Question 1

What is a race condition?

Answer 1

A condition that occurs when two concurrent programs interfere with each other

Question 2

What is a critical section?

Answer 2

A portion of code that shouldn’t be interrupted while its running.

Question 3

What are the three requirements for a solution to the critical section problem?

Answer 3

Mutual Exclusion
Progress
Bounded Waiting

Question 4

What is Mutual Exclusion?

Answer 4

A requirement that a solution for the critical section problem must have. If a process is in its critical section then no other processes can be executing their critical section.

Question 5

What is Progress?

Answer 5

A requirement that a solution for the critical section problem must have. If no process is executing its critical section and another process wishes to enter their critical section then it cannot be postponed indefinitely.

Question 6

What is Bounded Waiting?

Answer 6

A requirement that a solution for the critical section problem must have. A bound must exist on the number of times other process are allowed to enter their critical section.

Question 7

What is the Interrupt based solution?

Answer 7

The entry section disables interrupts for the program while the exit section enables interrupts for the program.

Question 8

What is Peterson’s Solution?

Answer 8

You have a variable called turn that indicates who turn it is to enter the critical section as well as a flag that indicates if a process is read to enter into the critical section.

Question 9

Why is it that Peterson’s Solution may not work on modern hardware?

Answer 9

Modern Hardware may reorder operations to make thee program more efficient resulting in a skewed result.

Question 10

What is a memory barrier?

Answer 10

Memory guarantees a computer architecture makes to application programs.

Question 11

What is the difference between a strongly ordered memory model and a weakly ordered memory model?

Answer 11

A strongly ordered memory model is one where a memory modification of one processor is visible to all other processors. A weakly ordered memory model is where a modification of one processor may not be immediately visible to all other processors.

Question 12

What are the two forms of hardware support for synchronization?

Answer 12

Hardware instructions
Atomic Variables

Question 13

What are atomic variables?

Answer 13

Variables that are guaranteed to not be able to interrupted in their operations

Question 14

What are the two Hardware Instructions that can be used to insure syncronization?

Answer 14

Test and Set and Compare and Swap

Question 15

What does Test and Set do?

Answer 15

It takes in a Boolean target, sets a return value equal to target sets target to true and then returns the return value
It is executed atomically

Question 16

What does the compare and swap function do?

Answer 16

Returns the original value of the passed parameter and sets the variable value to the value of the passed parameter only if value equals the expected variable.

Question 17

What are Mutex Locks?

Answer 17

A way to protect critical sections by acquiring locks then releasing them

Question 18

What is a downside of Mutex Locks?

Answer 18

It requires something called busy waiting which means that the threads that are waiting on the lock are consuming reasources

Question 19

What are Semaphores?

Answer 19

Integer variables that are incremented and decremented atomicly.

Question 20

What are Condition Variables?

Answer 20

Variables that can be suspended and woken up by signaling and waiting

Question 21

What is liveness?

Answer 21

A set of properties that a system must satisfy to ensure processes make progress (i.e. no indefinite waiting)

Question 22

What is a deadlock?

Answer 22

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

Question 23

What is the bounded-buffer synchronization problem?

Answer 23

You have n buffers, each of which can hold one item, a semaphore mutex initialized to the value 1 and a semaphore full initialized to the value 0 and a semaphore empty initialized to the value n. The producer produces something to place into the buffer while the consumer consumers what is placed in the buffer.

Question 24

What is the readers-writers problem?

Answer 24

The readers only read the data, they do not perform any updates, while the writers can both read and write. The problem involves how to have multiple readers to read at the same time.

Question 25

What is the difference between named and unnamed Semaphores?

Answer 25

Named semaphores can be used by unrelated processes, while unnamed semaphores cant.

Question 26

What is a memory transaction?

Answer 26

A sequence of read-write operations to memory that are performed atomically.