Quiz 4

Question 1

What are the three resource types in the system model?

Answer 1

CPU cycles, memory space, I/O devices

Question 2

In which way does each process utilizes a resource?

Answer 2

Request
Use
Release

Question 3

What are the four conditions required to have a Deadlock?

Answer 3

Mutual exclusion
Hold and wait
No preemption
Circular wait

Question 4

Mutual Exclusion

Answer 4

Only one process at a time can use a resource

Question 5

Hold and Wait

Answer 5

A process holding at least one resource is waiting to acquire additional resources held by other processes

Question 6

No Preemption

Answer 6

A resource can be released only voluntarily by the process holding it, after that process has completed its task

Question 7

Circular Wait

Answer 7

Each waiting process is waiting for a resource held by another process, where each of said processes are reliant on the other to give up their resource

Question 8

What is a resource allocation graph?

Answer 8

A resource allocation graph is a graph that shows the relationship between requests and resources held between processes

Question 9

If a graph contains no cycles this means what in reference to a deadlock?

Answer 9

No deadlock

Question 10

If a graph contains a cycle this means what in reference to a deadlock?

Answer 10

If only one instance per resource type then deadlock
else its only a possibility

Question 11

What are the two methods for preventing a deadlock state?

Answer 11

Deadlock prevention and Deadlock avoidance

Question 12

How does Deadlock Prevention prevent deadlocks?

Answer 12

It invalidates on of the four necessary conditions for deadlocks

Question 13

How does deadlock prevention invalidate mutual exclusion?

Answer 13

It makes it not required for sharable resources, this means non sharable resources can still result in a deadlock

Question 14

How does deadlock prevention invalidate Hold and Wait?

Answer 14

It must guarantee that whenever a process requests a resource it does not hold any other resource.

Question 15

How does deadlock prevention invalidate no Preemption?

Answer 15

If a process that is holding some resources requests another resource that cannot be immediately allocated to it then all resources currently being held are released

Question 16

How does deadlock prevention invalidate circular wait?

Answer 16

Impose a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration

Question 17

What is the most common type of deadlock prevention?

Answer 17

Invalidating circular wait

Question 18

How does deadlock avoidance avoid deadlocks?

Answer 18

By requesting additional a priori information to be available

Question 19

What is the a priori info that is typically requested for deadlock avoidance?

Answer 19

Each process declares the maximum number of resources of each type that it may need

Question 20

What must the system be in for a process request to be verified when the system is using deadlock avoidance?

Answer 20

A safe state

Question 21

When you have a single instance of a resource type which algorithm should you use?

Answer 21

A resource allocation graph

Question 22

When you have multiple instances of a resource type which algorithm should you use?

Answer 22

The bankers algorithm

Question 23

When can a request be granted for a request edge to an assignment edge?

Answer 23

As long as it does not result in the formation of a cycle

Question 24

What are the attributes of the Banker’s Algorithm?

Answer 24

You have multiple instances of resources
Each process must a priori claim maximum use
When a process requests a resource it may have to wait
When a process gets all its resources it must return them in a finite amount of time

Question 25

What is the overview for Deadlock detection?

Answer 25

Allow the system to enter the deadlock state, use a detection algorithm and then use a recovery scheme

Question 26

How do deadlock detection systems recover from a deadlock?

Answer 26

Abort all deadlocked processes
Abort one process at a time until the deadlock cycle is eliminated