Deadlock Avoidance: Identifying the Correct Algorithm Among Options

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Sep 12, 2026

Deadlock avoidance is a class of resource-allocation strategies that refuse to grant a request that would move the system into an unsafe state (i.e., a state where deadlock is possible). The canonical example in operating systems is the Banker's algorithm.

In contrast, options like round-robin are CPU scheduling policies rather than deadlock avoidance mechanisms, and “elevator” and “Karn’s” are not standard deadlock-avoidance algorithms in the classic OS taxonomy used in exams/textbooks.

A high-level decision rule for deadlock avoidance is:

Among the given choices, the deadlock avoidance algorithm is (i) Banker's algorithm.

Key terms you should recognize here:

Deadlock
Deadlock avoidance
Safe state
Resource allocation graph

Deadlock Avoidance (Banker's Algorithm) - OS Concepts

To map the multiple-choice options correctly, it helps to distinguish what kind of algorithm each option actually is:

(i) Banker's algorithm: designed specifically to avoid deadlocks by checking safety before granting resource requests. It matches the definition of deadlock avoidance.
(ii) Round-robin algorithm: a well-known time-slicing CPU scheduling approach. It does not analyze resource-allocation safety conditions, so it is not deadlock avoidance.
(iii) Elevator algorithm: typically refers to a disk head scheduling strategy (servicing requests like an elevator/SCAN). Again, not a resource-allocation deadlock method.
(iv) Karn's algorithm: “Karn’s algorithm” is not part of the standard OS deadlock avoidance/detection set used in canonical curricula and exam questions; it is therefore not the expected deadlock avoidance answer among these choices.

Why Banker's Algorithm is Deadlock Avoidance (Safety Check Process)

1
Step 1
Temporarily update the Available, Allocation, and Need structures as if the request were granted.
2
Step 2
Try to find a sequence of processes that can finish with the remaining resources.
3
Step 3
If such a sequence exists, the new state is safe → grant. If none exists, it’s unsafe → delay/deny.
4
Step 4
Repeat the safety check whenever a new request arrives.

Visualizing “safe vs unsafe”

A “safe” state means there exists at least one ordering of process completions that avoids deadlock. “Unsafe” does not mean deadlock is guaranteed immediately; it means deadlock is possible, so the system avoids granting actions that create such states.

Algorithm Type vs Relevance to Deadlock Avoidance

High relevance means the algorithm actively prevents unsafe resource-allocation grants.

Exam Strategy

If an option mentions resource allocation + safe/unsafe states, it’s usually deadlock avoidance. Round-robin and elevator are scheduling policies, not resource-allocation safety checks.

Common Confusion

Round-robin is about CPU time sharing. Deadlock is about processes waiting for resources. Don’t mix scheduling with deadlock-avoidance conditions.

Quick Explanations of Each Option

Knowledge Check

Question 1 of 3

Q1Single choice

Which one of the following is the deadlock avoidance algorithm?

Banker's algorithm

Round-robin algorithm

Elevator algorithm

Karn's algorithm

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Banker's Algorithm Safe-State Analysis for Processes $P_0$ Through $P_4$

The course walks through a full Banker's‑algorithm safety analysis for processes  $P_0$ – $P_4$ , computing the Need matrix and using the work‑vector test to verify a safe state and a valid completion order.

Need matrix: $P_0\;(0,0,0,0)$ , $P_1\;(0,7,5,0)$ , $P_2\;(1,0,0,2)$ , $P_3\;(0,0,2,0)$ , $P_4\;(0,6,4,2)$ .
Starting work $Work = Available = (1,5,2,0)$ ; each step selects a process with $Need \le Work$ , releases its allocation, and updates $Work$ .
All processes finish, yielding a safe sequence $\langle P_0, P_2, P_1, P_3, P_4\rangle$ .
A safe state requires only one such sequence; it does not mean every immediate allocation is safe.
Exam tip: test processes with minimal or zero Need first to unlock the rest.

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