CS400 Operating Systems
Homework #6
Due before next class.
Turn in your HW on SCANTRON answer sheet to your graders.
Turn in your HW on Santron answer sheet to your graders.
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Student ID:
Name:
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1. 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
2. One necessary condition for deadlock is ____, which states that at least one resource must be
held in a non-sharable mode.
a) hold and wait
b) mutual exclusion
c) circular wait
d) no preemption
3. 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
4. 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
5. 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.
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a) hold and wait
b) mutual exclusion
c) circular wait
d) no preemption
6. Deadlock prevention and deadlock avoidance are essentially the same approaches for
handling deadlock.
a) True
b) False
7. In a system resource-allocation graph, a directed edge from a process to a resource is called
____.
a) an assignment edge
b) a claim edge
c) a request edge
d)None of the above
8. 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) neither necessary nor sufficient for indicating deadlock in the case that each resource has
exactly one instance
9. 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
10. Which of the following statements is true?
a) A safe state is a deadlocked state.
b) A safe state may lead to a deadlocked state.
c) An unsafe state is necessarily, and by definition, always a deadlocked state.
d) An unsafe state may lead to a deadlocked state.
11. 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. Which of the
following correctly characterizes this state?
Process Maximum Needs Currently Owned
P0
10
4
2
P1
3
1
P2
6
4
a) It is safe.
b) It is not safe.
c) The state cannot be determined.
d) It is an impossible state.
12. Suppose that there are 12 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. Which of the
following correctly characterizes this state?
Process Maximum Needs Currently Owned
P0
10
4
P1
3
2
P2
7
4
a) It is safe.
b) It is not safe.
c) The state cannot be determined.
d) It is an impossible state.
13. 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
14. 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
15. Deadlock ___________________ is a set of methods for ensuring that at least one of
the necessary conditions for deadlock cannot hold.
a) prevention
b) avoidance
c) detection and recovery
16. Deadlock ____________ requires that the operating system be given, in advance, additional
information concerning which resources a process will request and use during its lifetime.
a) prevention
b) avoidance
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c) detection and recovery
17. Which of the following is not the solution to ensure that the hold-and-wait condition never
occurs in a system.
a) impose a total ordering of all resource types, and to require that each process requests
resources in an increasing order of enumeration.
b) One protocol requires each process to request and be allocated all its resources before it
begins execution.
c) An protocol allows a process to request resources only when it has none.
d) Before a process can request any additional resources, it must release all the resources that
it is currently allocated.
18. What is one way to ensure that a circular-wait condition does not occur?
a) Impose a total ordering of all resource types, and to require that each process requests
resources in an increasing order of enumeration.
b) One protocol requires each process to request and be allocated all its resources before it
begins execution.
c) A protocol allows a process to request resources only when it has none.
d) Before a process can request any additional resources, however, it must release all the
resources that it is currently allocated.
19. A(n) ___ edge indicates that a process may request a resource at some time in the future. It
is represented in the resource-allocation graph by a dashed line.
a) claim
b) Request
c) Assignment
d) Allocation
20. There are two methods for eliminating processes by aborting a process. The first method is
to abort all deadlocked processes. The second method is to abort one process at a time until
the deadlock cycle is eliminated. Which method will need to run deadlock-detection
algorithm?
a) The first method.
b) The second method.
21. There are two methods for eliminating processes by aborting a process. The first method is
to abort all deadlocked processes. The second method is to abort one process at a time until
the deadlock cycle is eliminated. The ____ method could terminate more processes than
necessary processes to remove the deadlock, while the __________ could run slower to fix
the deadlock problem since a deadlock detection is run after each process is removed.
a) 1st, 2nd.
b) 2nd, 1st
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22. A safe state ensures that there is a sequence of processes to finish their program execution.
Deadlock is not possible while the system is in a safe state. One technique for avoiding
deadlock is to ensure that the system always stays in a safe state.
a) True
b) False
23. If a system goes from a safe state to an unsafe state, deadlock is possible.
a) True
b)False
24. The circular-wait condition for a deadlock implies the hold-and-wait condition.
A) True
B) False
25. If a resource-allocation graph has a cycle, the system must be in a deadlocked state.
A) True
B) False
26. Protocols to prevent hold-and-wait conditions typically also prevent starvation.
A) True
B) False
27. The wait-for graph scheme is not applicable to a resource allocation system with multiple
instances of each resource type.
A) True
B) False
28. The banker's algorithm is useful in a system with multiple instances of each resource type
which wait-for graph scheme is not applicable to.
A) True
B) False
29. Ordering resources and requiring the resources to be acquired in order prevents the circular
wait from occurring and therefore prevents deadlock from occurring.
A) True
B) False
30. A system in an unsafe state will ultimately deadlock.
A) True
B) False
31. Deadlock prevention and deadlock avoidance are essentially the same approaches for
handling deadlock.
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a) True
b) False
32. Given a priori information about the ________ number of resources of each type that maybe
requested for each process, it is possible to construct an algorithm that ensures that the
system will never enter a deadlock state.
a) minimum
b)average
c) maximum
d)approximate
33. A deadlock avoidance algorithm dynamically examines the __________, to ensure that a
circular wait condition can never exist.
a) resource allocation state
b)system storage state
c) operating system
d)resources
34. A state is safe if _______.
a) the system does not crash due to deadlock occurrence
b)the system can allocate resources to each process in some order and still avoid a deadlock
c) the state keeps the system protected and safe
d)All of these
35. A system is in a safe state only if there exists a _______.
a) safe allocation
b) safe resource
c) safe sequence
d) All of these
36. A system has 12 magnetic tape drives and 3 processes : P0, P1, and P2.
Process Maximum needs allocated
P0
10
5
P1
4
2
P2
9
2
37. What are the current available resources?
a) 3
b)4
c) 5
d)6
38. (Continue the above question.) Which of the following sequence is a safe sequence?
a) P0, P1, P2
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b)P1, P2, P0
c) P2, P0, P1
d)P1, P0, P2
39. The resource allocation graph is not applicable to a resource allocation system _____.
a) with multiple instances of each resource type
b)with a single instance of each resource type
c) Both a and b
40. The Banker's algorithm is _____________ than the resource allocation graph algorithm.
a) less efficient
b)more efficient
c) None of these
41. The data structures available in the Banker's algorithm does not include
a) Available
b)Need
c) Allocation
d)Maximum
e) Minimum
42. A system with 5 processes P0 through P4 and three resource types A, B and C. At time t0,
the following snapshot has been taken:
Total number of resources
A
B
C
10 5
7
Allocation (process-wise: P0 through P4 top to bottom)
A
B
C
P0 0
1
0
P1 2
0
0
P2 3
0
2
P3 2
1
1
P4 0
0
2
Max (process-wise: P0 through P4 top to bottom)
A
B
C
P0 7
5
3
P1 3
2
2
P2 9
0
2
P3 2
2
2
P4 4
3
3
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43. What are the available resources per each type?
Available resources
A
B
C
a)
3
3
2
b)
2
3
2
c)
3
3
3
d)
2
2
3
e)
3
3
4
44. (Continue) The sequence leads the system to :
a) an unsafe state
b)a safe state
c) a protected state
d)a deadlock
45. Each request requires that the system consider the __________, _____________,
____________ to decide whether the current request can be satisfied or must wait to avoid a
future possible deadlock. (choose three)
a) resources currently available
b) processes that have previously been in the system
c) resources currently allocated to each process
d) future requests and releases of each process
46. A computer system has 6 tape drives, with 'n' processes competing for them. Each process
may need 3 tape drives. The maximum value of 'n' for which the system is guaranteed to be
deadlock free is _______.
a) 2
b)3
c) 4
d)1
47. Which of the following is not a disadvantage of the banker’s algorithm:
a) The numbers of processes and resources have to be fixed.
b)All processes must know and state their maximum resource need in advance.
c) All processes must terminate and release all its resouces in a finite amount of time.
d)The system can be less productive than the deadlock prevention method.
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