Deck 6: Synchronization Tools

Question 1

Which of the following regarding mutex lock is NOT true?

A) mutex lock is a hardware solution to critical-section problem
B) mutex lock is a higher-level software solution to critical-section problem
C) mutex lock suffers from busy waiting
D) the general rule of thumb is to use a mutex lock if the lock will be held for a duration less than two context switches

Answer 1

A

Question 2

Assume count is a variable name, which of the following operations is atomic?

A) count++
B) count--
C) both of the above
D) none of the above

Answer 2

D

Question 3

Which of the following is not true about test_and_set instruction?

A) It is a hardware instruction
B) It is executed atomically
C) Returns the original value of passed parameter
D) Returns the new value of passed parameter
E) Set the new value of passed parameter to "TRUE"

Answer 3

D

Question 4

In _________, the process requests permission to access and modify variables shared with others.

A) entry section
B) critical section
C) exit section
D) remainder section

Question 5

Which of the following critical-section problem's requirements ensures programs will cooperatively determine what process will next enter its critical section?

A) mutual exclusion
B) progress
C) bounded waiting
D) none of the above

Question 6

Which of the following is true for race condition?

A) race condition occurs where several processes access and manipulate the same data concurrently
B) when race condition occurs, the outcome of the execution depends on the particular order in which the access takes place
C) both of the above
D) none of the above

Question 7

Which of the following actions should be performed among cooperating processes?

A) process synchronization
B) coordination
C) both of the above
D) none of the above

Question 8

Which of the following variables are shared between the processes in Peterson's solution?

A) int turn
B) boolean flag[2]
C) both of the above
D) none of the above

Question 9

Which of the following critical-section problem's requirements ensures only one process is active in its critical section at a time?

A) mutual exclusion
B) progress
C) bounded waiting
D) none of the above

Question 10

Which of the following is true regarding the requirements for the solutions to critical-section problem?

A) mutual exclusion implies progress
B) progress implies bounded waiting
C) bounded waiting implies progress
D) none of the above

Question 11

Assume the binary variable lock is initialized to be 0, which of the following can be an implementation of the entry section to solve the critical-section problem?

A) while (compare and swap(&lock, 0, 1) != 0), do nothing;
B) while (test and set(&lock)), do nothing;
C) both A and B
D) none of the above

Question 12

Which of the following indicates that P_i can enter the critical section in Peterson's solution?

A) flag[j] == false or turn == i
B) flag[j] == true or turn == i
C) flag[j] == false or turn == j
D) flag[j] == true and turn == j

Question 13

Which of the following is a software-based solution to the critical-section problem?

A) Peterson's solution
B) test_and_set
C) compare_and_swap
D) all of the above

Question 14

Which of the following is not true about compare_and_swap instruction?

A) It is a hardware instruction
B) It is executed atomically N) Returns the original value of passed parameter
D) Set the new value of passed parameter to "TRUE"
E) Set the variable "value" the value of the passed parameter "new_value" but only if "value" =="expected"

Question 15

Which of the following critical-section problem's requirements limits the amount of time a program will wait before it can enter its critical section?

A) mutual exclusion
B) progress
C) bounded waiting
D) none of the above

Question 16

Which of the following solutions needs hardware support for the critical section problem?

A) memory barriers
B) compare_and_swap instruction
C) atomic variables
D) all of the above

Question 17

Which of the following is NOT true for Peterson's solution?

A) Mutual exclusion is preserved
B) The progress requirement is satisfied
C) The bounded-waiting requirement is met
D) Peterson's solution works for synchronization among more than two processes

Question 18

When mutex lock is implemented as a binary semaphore, what should its value be initialized to be?

A) 0
B) 1
C) -1
D) none of the above

Question 19

Which of the following is true for the solutions to critical-section problems?

A) No deadlock implies progress, and progress implies bounded waiting
B) Bounded waiting implies progress, and progress implies no deadlock
C) Progress implies no deadlock, and no deadlock implies bounded waiting
D) Bounded waiting implies no deadlock, and no deadlock implies progress

Question 20

In _________, the process may be changing common variables, updating a table, writing a file, and so on.

A) entry section
B) critical section
C) exit section
D) remainder section

Question 21

What is the correct order of operations for protecting a critical section using a binary semaphore?

A) release() followed by acquire()
B) acquire() followed by release()
C) wait() followed by signal()
D) signal() followed by wait()

Question 22

Explain what busy waiting is.

Question 23

The counting semaphore is initialized to ___________.

A) 0
B) 1
C) the number of resources available
D) none of the above

Question 24

What is the difference between counting semaphore and binary semaphore.

Question 25

Which of the following statements is true?

A) A counting semaphore can never be used as a binary semaphore.
B) A binary semaphore can never be used as a counting semaphore.
C) Spinlocks can be used to prevent busy waiting in the implementation of semaphore.
D) Counting semaphores can be used to control access to a resource with a finite number of instances.

Question 26

Under which of the following contention loads does traditional synchronization become faster than CAS-based synchronization?

A) uncontended
B) moderate contention
C) high contention
D) none of the above

Question 27

What is meant by "short duration"?

Question 28

Which of the following is NOT true regarding semaphore implementation?

A) It suffers from the busy waiting problem
B) Semaphore has a waiting queue associated with the semaphore
C) When a process executes the wait() operation and finds that the semaphore value is not positive, it will suspend itself
D) A process that is suspended, waiting on the semaphore, should be restarted when some other process executes a signal() operation.

Question 29

Which of the following is true?

A) No deadlock implies no starvation;
B) No starvation implies no deadlock;
C) Deadlock doesn't imply starvation;
D) Starvation implies deadlock.

Question 30

Which of the following may cause a liveness failure?

A) an infinite loop
B) a busy waiting loop
C) a deadlock
D) all of the above

Question 31

What is the difference between semaphore and mutex lock?

Question 32

Which of the following are efforts to towards developing scalable, efficient tools that address the demands of concurrent programming?

A) designing compilers that generate more efficient code
B) developing languages that provide support for concurrent programming
C) improving the performance of existing libraries and APIs
D) all of the above

Question 33

Explain how semaphore implementation overcomes the busy waiting problem of mutex lock.

Question 34

Assume you had a function named update() that updates shared data. Illustrate how a mutex lock named mutex might be used to prevent a race condition in update().

Question 35

Explain what critical section problem is.

Question 36

Explain two general approaches to handle critical sections in operating systems.

Question 37

Which of the following is NOT true?

A) Since semaphore and mutex lock are tools for synchronization, process that have used semaphores or mutex locks should not cause deadlocks
B) Semaphores and mutex locks may be shared resources that difference processes contend for, and hence deadlocks may occur
C) a set of processes is in a deadlocked state when every process in the set is waiting for an event that can be caused only by another process in the set
D) all of the above

Question 38

Explain what race condition is.

Question 39

Which of the following is NOT true regarding conditional variable, e.g. x?

A) The only operations that can be invoked on a condition variable are wait() and signal()
B) x.wait() means that the process invoking this operation is suspended until another process invokes x.signal()
C) The x.signal() operation resumes exactly one suspended process
D) If no process is suspended, then the signal() operation still affects the state of the semaphore

Question 40

What three conditions must be satisfied in order to solve the critical section problem?

Question 41

Mutex locks and counting semaphores are essentially the same thing.

Question 42

Semaphore implementation overcomes the busy waiting problem.

Question 43

Semaphores and mutex locks both provide mutual exclusion.

Question 44

A semaphore has an integer value.

Question 45

The preemptive kernel is more suitable for real-time programming than non-preemptive kernel.

Question 46

Write two short methods that implement the simple semaphore wait() and signal() operations on global variable S.

Question 47

Solutions to the critical section problem may suffer from liveness failures.

Question 48

The value of a counting semaphore can range only between 0 and 1.

Question 49

Peterson's solution works on modern computer architectures.

Question 50

A monitor is an abstract data type that is based on semaphore implementation.

Question 51

A mutex lock is released immediately after entering a critical section.

Question 52

What is the difference between a semaphore and conditional variable?

Question 53

Spinlocks are not appropriate for single-processor systems.

Question 54

Explain what a deadlock is.

Question 55

When the mutex lock is implemented based on a binary semaphore, it should be initialized to be 0.

Question 56

The preemptive kernel may be more responsive than non-preemptive kernel.

Question 57

Race conditions can result in corrupted values of shared data.

Question 58

Mutex lock variable is binary.

Question 59

Bounded waiting implies progress, and progress implies mutual exclusion.

Question 60

Every object in Java has associated with it a single lock.

Question 61

CAS-based synchronization is always faster than traditional synchronization.