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CS 410 Unit 5

Terms in this set (63)

A race condition ____.
A) results when several threads try to access the same data concurrently
B) results when several threads try to access and modify the same data concurrently
C) will result only if the outcome of execution does not depend on the order in which instructions are executed
D) None of the above
B) results when several threads try to access and modify the same data concurrently
Instructions from different processes can be interleaved when interrupts are allowed.
True
False
True
A(n) _______ refers to where a process is accessing/updating shared data.
A) critical section
B) entry section
C) mutex
D) test-and-set
A) critical section
A solution to the critical section problem does not have to satisfy which of the following requirements?
A) mutual exclusion
B) progress
C) atomicity
D) bounded waiting
C) atomicity
A nonpreemptive kernel is safe from race conditions on kernel data structures.
True
False
True
An instruction that executes atomically ____.
A) must consist of only one machine instruction
B) executes as a single, uninterruptible unit
C) cannot be used to solve the critical section problem
D) All of the above
B) executes as a single, uninterruptible unit
Race conditions are prevented by requiring that critical regions be protected by locks.
True
False
True
Both the test_ and_set() instruction and compare_and_swap() instruction are executed atomically.
True
False
True
A mutex lock ____.
A) is exactly like a counting semaphore
B) is essentially a boolean variable
C) is not guaranteed to be atomic
D) can be used to eliminate busy waiting
B) is essentially a boolean variable
What is the correct order of operations for protecting a critical section using mutex locks?
A) release() followed by acquire()
B) acquire() followed by release()
C) wait() followed by signal()
D) signal() followed by wait()
B) acquire() followed by release()
Busy waiting refers to the phenomenon that while a process is in its critical section, any other process that tries to enter its critical section must loop continuously in the call to acquire the mutex lock.
Yes
No
Yes
A counting semaphore ____.
A) is essentially an integer variable
B) is accessed through only one standard operation
C) can be modified simultaneously by multiple threads
D) cannot be used to control access to a thread's critical sections
A) is essentially an integer variable
_____ can be used to prevent busy waiting when implementing a semaphore.
A) Spinlocks
B) Waiting queues
C) Mutex lock
D) Allowing the wait() operation to succeed
B) Waiting queues
Mutex locks and binary semaphores are essentially the same thing.
True
False
True
A ___ type presents a set of programmer-defined operations that are provided mutual exclusion within it.
A) transaction
B) signal
C) binary
D) monitor
D) monitor
The local variables of a monitor can be accessed by only the local procedures.
True
False
True
Monitors are a theoretical concept and are not practiced in modern programming languages
True
False
False
A deadlock-free solution eliminates the possibility of starvation.
True
False
False
Another problem related to deadlocks is ____________.
A) race conditions
B) critical sections
C) spinlocks
D) indefinite blocking
D) indefinite blocking
____________ occurs when a higher-priority process needs to access a data structure that is currently being accessed by a lower-priority process.
A) Priority inversion
B) Deadlock
C) A race condition
D) A critical section
A) Priority inversion
Traditional synchronization is always much faster than CAS-based synchronization.
True
False
False
What is the purpose of the mutex semaphore in the implementation of the bounded-buffer problem using semaphores?
A) It indicates the number of empty slots in the buffer.
B) It indicates the number of occupied slots in the buffer.
C) It controls access to the shared buffer.
D) It ensures mutual exclusion.
D) It ensures mutual exclusion.
The first readers-writers problem ____.
A) requires that, once a writer is ready, that writer performs its write as soon as possible.
B) is not used to test synchronization primitives.
C) requires that no reader will be kept waiting unless a writer has already obtained permission to use the shared database.
D) requires that no reader will be kept waiting unless a reader has already obtained permission to use the shared database.
C) requires that no reader will be kept waiting unless a writer has already obtained permission to use the shared database.
How many philosophers may eat simultaneously in the Dining Philosophers problem with 5 philosophers?
A) 1
B) 2
C) 3
D) 5
B) 2
Which of the following statements is true?
A) Operations on atomic integers do not require locking.
B) Operations on atomic integers do require additional locking.
C) Linux only provides the atomic_inc() and atomic_sub() operations.
D) Operations on atomic integers can be interrupted.
A) Operations on atomic integers do not require locking.
A thread will immediately acquire a dispatcher lock that is the signaled state.
True
False
True
Linux mostly uses atomic integers to manage race conditions within the kernel.
True
False
False
Pthreads can be implemented
A) only inside the operating system kernel
B) only at the user level
C) at the user level or inside the operating system kernel
D) only Windows OS
C) at the user level or inside the operating system kernel
When the owner of a mutex lock invokes pthread mutex unlock(), all threads blocked on that mutex's lock are unblocked.
True
False
False
A call to pthread_cond_signal()
A) releases the mutex lock and signals one thread waiting on the condition variable.
B) releases the mutex lock and signals all threads waiting on the condition variable.
C) signals one thread waiting on the condition variable, but does not release the mutex lock.
D) signals all threads waiting on the condition variable, but does not release the mutex lock.
C) signals one thread waiting on the condition variable, but does not release the mutex lock.
A deadlocked state occurs whenever ____.
A) a process is waiting for I/O to a device that does not exist
B) the system has no available free resources
C) every process in a set is waiting for an event that can only be caused by another process in the set
D) a process is unable to release its request for a resource after use
C) every process in a set is waiting for an event that can only be caused by another process in the set
Deadlock occurs when every thread in a set is blocked waiting for an event that can be caused only by another thread in the set, while livelock occurs when a thread continuously attempts an action that fails.
True
False
True
In the dining philosophers problem, there is a possibility of deadlock but not livelock.
True
False
False
One necessary condition for deadlock is ____, which states that a process must be holding one resource and waiting to acquire additional resources.
A) hold and wait
B) mutual exclusion
C) circular wait
D) no preemption
A) hold and wait
A cycle in a resource-allocation graph is ____.
A) a necessary and sufficient condition for deadlock in the case that each resource has more than one instance
B) a necessary and sufficient condition for a deadlock in the case that each resource has exactly one instance
C) a sufficient condition for a deadlock in the case that each resource has more than once instance
D) is neither necessary nor sufficient for indicating deadlock in the case that each resource has exactly one instance
B) a necessary and sufficient condition for a deadlock in the case that each resource has exactly one instance
If a resource-allocation graph has a cycle, the system must be in a deadlocked state.
True
False
False
To handle deadlocks, operating systems most often ____.
A) pretend that deadlocks never occur
B) use protocols to prevent or avoid deadlocks
C) detect and recover from deadlocks
D) None of the above
A) pretend that deadlocks never occur
Both deadlock prevention and deadlock avoidance techniques ensure that the system will never enter a deadlocked state.
True
False
True
Most operating systems choose to ignore deadlocks, because
A) handling deadlocks is expensive in terms of performance and resources.
B) deadlocks occur infrequently.
D) methods used to recover from livelock may be put to use to recover from deadlock.
D) All of the above.
D) All of the above.
Assume there are three resources, R1, R2, and R3, that are each assigned unique integer values 15, 10, and 25, respectively. What is a resource ordering which prevents a circular wait?
A) R1, R2, R3
B) R3, R2, R1
C) R3, R1, R2
D) R2, R1, R3
D) R2, R1, R3
Deadlock prevention by denying the mutual-exclusion condition is the simplest way to prevent deadlocks.
True
False
False
In deadlock prevention by denying hold-and-wait condition,
A) resource utilization may be low.
B) starvation is possible.
C) whenever a thread requests a resource, it does not hold any other resources.
D) All of the above.
D) All of the above.
What are the three criteria necessary for a solution to the critical section problem?
Mutual Exclusion
Progress
Bounded Waiting
List and briefly describe each of the four necessary conditions for a deadlock.
Mutual Exlusion
A process can be the only process aloud to use a resource at a time.
Hold and Wait
A process restricting a resource while waiting for more resources to free up.
No preemption
Processes must voluntarily give up resources
Circular wait
Processes wait in a loop because the resource they need is held by the previous process
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
C) both of the above
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
C) both of the above
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
B) critical section
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
A) entry section
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
D) none of the above
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
D) all of the above
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
A) mutex lock is a hardware solution to critical-section problem
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
B) 1
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.
A) It suffers from the busy waiting problem
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.
C) Spinlocks can be used to prevent busy waiting in the implementation of semaphore.
(Refer to section 6.7.1) 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
D) If no process is suspended, then the signal() operation still affects the state of the semaphore
In the structure of the producer process shown in Figure 7.1, what would be a possible outcome if wait(empty) is replaced with signal(empty) and signal(full) is replaced with wait(full)?
A) Producer will remain blocked after adding an item in the buffer.
B) Consumer will remain blocked after taking out an item from the buffer.
C) Producer and consumer may access the buffer at the same time.
D) All of the above.
A) Producer will remain blocked after adding an item in the buffer.
A reader-writer lock is useful when
A) there are a significantly large number of processes attempting to enter a critical section.
B) there are a significantly large number of consumer processes attempting to read data from a bounded buffer.
C) there are a significantly small number of reader processes attempting to read in the critical section.
D) there are a significantly large number of reader processes attempting to read in the critical section.
D) there are a significantly large number of reader processes attempting to read in the critical section.
Which of the following statements is not true about spinlocks in Linux?
A) Spinlocks cannot be used on single processor machines.
B) A thread may disable kernel preemption on Symmetric Multi Processing machines instead of acquiring spinlocks.
C) A thread that acquires a spinlock cannot acquire the same lock a second time without first releasing the lock.
D) The Linux kernel is designed so that the spinlock is held only for only short durations.
B) A thread may disable kernel preemption on Symmetric Multi Processing machines instead of acquiring spinlocks.
Atomic integers in Linux are useful when
A) several variables are involved in a race condition.
B) a single process access several variable involved in a race condition.
C) an integer variable needs to be updated.
D) All of the above.
C) an integer variable needs to be updated.
In the deadlock example shown in Figure 8.1,
A) a deadlock is guaranteed to occur.
B) a deadlock may occur sometime, but not necessarily every time.
C) a deadlock may occur sometime only if there are more than one instances of thread_one and thread_two are running.
D) a deadlock is guaranteed to occur as long as there are more than one instances of thread_one and thread_two are running.
B) a deadlock may occur sometime, but not necessarily every time.
In the livelock example shown in Figure 8.2,
A) a livelock is guaranteed to occur.
B) a livelock may occur sometime.
C) a livelock may occur sometime only if there are more than one instances of thread_one and thread_two are running.
D) a livelock is guaranteed to occur as long as there are more than one instances of thread_one and thread_two are running.
C) a livelock may occur sometime only if there are more than one instances of thread_one and thread_two are running.
One necessary condition for deadlock is ______, which states that a resource can be released only voluntarily by the process holding the resource.
A) hold and wait
B) mutual exclusion
C) circular wait
D) no preemption
D) no preemption
One necessary condition for deadlock is ______, which states that there is a chain of waiting processes whereby P0 is waiting for a resource held by P1, P1 is waiting for a resource held by P2, and Pn is waiting for a resource held by P0.
A) hold and wait
B) mutual exclusion
C) circular wait
D) no preemption
C) circular wait
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