This document summarizes key concepts related to deadlock avoidance in operating systems. It discusses the four conditions for deadlock, describes the concept of a safe state for resource allocation, and provides an example of modeling resource allocation using a resource allocation graph. The document is presented as part of a course on operating systems, covering topics such as deadlock avoidance, safe state determination, and modeling resource allocation through graphs.

1. Pundra University Of Science & Technology
Name: Shayek Parvez
CSE 3rd Batch, 7th semester
Roll No: C00315306010
Course Title: Operating System
Course Code: 313
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2. Presentation Topic
Deadlock avoidance, Safe State,
Resource Allocation Graph
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3. What is Deadlock avoidance
Deadlock is: A set of blocked processes each
holding a resource and waiting to acquire a
resource held by another process in the set.
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4. The Conditions for Deadlock
1. Mutual Exclusion
• Only one process at a time may use a resource
2. Hold-and-Wait
• A process may hold allocated resources while awaiting
assignment of others
3. No Preemption
• A resource can be released only voluntarily by the
process holding it, after that process has completed its
Task
4. Circular Wait
• a closed chain of processes exists, such that each
process holds at least one resource needed by the next
process in the chain
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5. Safe State
Q: Suppose there are four process in Execution with 12 instances of a Resources R
in a System. The Maximum need of each process & current allocation are given below.
Process Max Need Current Allocation
P1 8 3
P2 9 4
P3 5 2
P4 3 1
Ans: Total Resources = 12
Process Max Need Current
Allocation
Future
Allocation
P1 8 3 5
P2 9 4 5
P3 5 2 3
P4 3 1 2
10 resources allocated, 2 resources available
P4 = 1+2 = 3
P3 = 3+2 = 5
P2 = 4+5 = 9
P1 = 3+5 = 8
So the Answer Will be P4,P3,P1,P2 Page: 5/7

6. OS - Resource Allocation Graph
P1 P2 P3
R1 R2
R3 R4
Resource Allocation Graph
Process
Resources
Not Sharable
(only 1 process can be accessed)
instance
(sharable, can be allocated
2 processes at a time)
Allocation edge
(Directed Resource to Process)
Request edge
(Directed Process to Resource)
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7. Thank You