Deck 8: Deadlocks

Question 1

Which of the following statement is true?

A) An unsafe state is a deadlocked state.
B) A deadlocked state is a safe state.
C) An unsafe state will lead to a deadlocked state.
D) An unsafe state may lead to a deadlocked state.

Answer 1

D

Question 2

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.

Answer 2

B

Question 3

The Linux Lockdep tool is

A) used to verify locking order in the kernel.
B) a modeler to develop resource allocation graphs
C) a driver that can be used to prevent mutual exclusion for nonsharable resources
D) an implementation of the banker's algorithm available for most operating systems

Answer 3

A

Question 4

Deadlocks can be prevented only if

A) all four necessary conditions cannot hold.
B) at least one of the four necessary conditions cannot hold.
C) mutual exclusion condition cannot hold.
D) circular wait condition cannot hold.

Question 5

In a system resource-allocation graph, ____.

A) a directed edge from a process to a resource is called an assignment edge
B) a directed edge from a resource to a process is called a request edge
C) a directed edge from a process to a resource is called a request edge
D) None of the above

Question 6

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.

Question 7

In a system resource-allocation graph, ____.

A) a directed edge from a resource to a process is called an assignment edge
B) a directed edge from a resource to a process is called a request edge
C) a directed edge from a process to a resource is called an assignment edge
D) None of the above

Question 8

Suppose that there are ten resources available to three processes. At time 0, the following data is collected. The table indicates the process, the maximum number of resources needed by the process, and the number of resources currently owned by each process. Process Maximum Needs Currently Owned
P₀ 10 4
P₁ 3 1
P₂ 5 4
At time 1, P1 requests a resource. Which of the following is correct?

A) The request will be granted, since the current state is safe.
B) The request will not be granted, since the current state is not safe.
C) The request will be granted, since the state after granting the request will be safe.
D) The request will not be granted, since the state after granting the request will be unsafe.

Question 9

A claim edge in a resource-allocation graph indicates that

A) a process has been allocated a resource.
B) a process may request a resource.
C) a process may release a resource that it has already been assigned.
D) a process has requested a resource.

Question 10

One necessary condition for deadlock is ____, which states that at least one resource must be held in a nonsharable mode.

A) hold and wait
B) mutual exclusion
C) circular wait
D) no preemption

Question 11

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

Question 12

Which of the following is not a factor in choosing which process to terminate during recovery from a deadlock?

A) Who the parent of the process is.
B) How many more resources the process needs in order to complete.
C) How many processes will need to be terminated.
D) What the priority of the process is

Question 13

In a resource allocation graph, when a process releases a resource,

A) a request edge is inserted.
B) an assignment edge is inserted.
C) a request edge is removed.
D) an assignment edge is removed.

Question 14

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 P_n is waiting for a resource held by P₀.

A) hold and wait
B) mutual exclusion
C) circular wait
D) no preemption

Question 15

Suppose that there are two resource types (R1 and R2) with five resources each available to four processes. At time 0, the following data is collected. The table indicates the process, the number of resources of each type currently allocated to the processes, and the current request of each resource type by each process. Process Allocation Request
R1 R2 R1 R2
P₀ 2 0 3 2
P₁ 1 1 1 0
P₂ 0 1 1 1
P₃ 1 1 3 2
Which of the following sentences is correct?

A) All four processes are currently deadlocked.
B) The system is not deadlocked.
C) Processes P₀ and P₃ are deadlocked.
D) Processes P₀, P₁ and P₃ are deadlocked.

Question 16

Deadlock prevention using preempting allocated resources cannot be used for

A) mutexes.
B) CPU registers.
C) database transactions.
D) memory.

Question 17

In a system that uses deadlock detection algorithm,

A) a deadlock is detected as soon as it occurs.
B) a deadlock is detected just before it occurs.
C) a deadlock is detected sometime after it has occurred but not necessarily immediately.
D) a deadlock is detected sometime before it occurs, but not necessarily just before.

Question 18

A _____ could be preempted from a process.

A) mutex lock
B) CPU registers
C) semaphore
D) file lock

Question 19

Which of the following data structures in the banker's algorithm is a vector of length m, where m is the number of resource types?

A) Need
B) Allocation
C) Max
D) Available

Question 20

A system will never enter a deadlocked state if

A) the system chooses to ignore the problem altogether.
B) the system uses the detection and recovery technique.
C) the system uses the deadlock avoidance technique.
D) None of the above.

Question 21

Describe a wait-for graph and how it detects deadlock.

Question 22

Explain what has to happen for a set of processes to achieve a deadlocked state.

Question 23

The circular-wait condition for a deadlock implies the hold-and-wait condition.

Question 24

Ordering resources and requiring the resources to be acquired in order prevents the circular wait from occurring and therefore prevents deadlock from occurring.

Question 25

Describe two protocols to ensure that the hold-and-wait condition never occurs in a system.

Question 26

What is one way to ensure that a circular-wait condition does not occur?

Question 27

What does a claim edge signify in a resource-allocation graph?

Question 28

Protocols to prevent hold-and-wait conditions typically also prevent starvation.

Question 29

Recovery from a deadlock works best when a single process can be identified whose termination will break the circular wait.

Question 30

Describe how a safe state ensures deadlock will be avoided.

Question 31

Deadlock prevention and deadlock avoidance are essentially the same approaches for handling deadlock.

Question 32

A system in an unsafe state will ultimately deadlock.

Question 33

What are the three general ways that a deadlock can be handled?

Question 34

The banker's algorithm is useful in a system with multiple instances of each resource type.

Question 35

Describe the four conditions that must hold simultaneously in a system if a deadlock is to occur.

Question 36

What is the difference between deadlock prevention and deadlock avoidance?

Question 37

If the sum of all needs for a resource type exceeds the available number of instances of that resource type, the system state is unsafe.

Question 38

What factors influence the decision of when to invoke a detection algorithm?

Question 39

Name three issues that need to be addressed if a preemption is required to deal with deadlocks.

Question 40

Describe two methods for eliminating deadlock by aborting a process.