GATE CS 2025 Set 2 — Question 48
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Operating System → Deadlocks → Deadlock Recovery
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Question
consists of all active processes in an operating system.
consists of single instances of distinct types of resources in the system.The resource allocation graph has the following assignment and claim edges.Assignment edges: (the assignment edge means resource is assigned to process , and so on for others)Claim edges: (the claim edge means process is waiting for resource , and so on for others)Which of the following statement(s) is/are CORRECT?
consists of single instances of distinct types of resources in the system.The resource allocation graph has the following assignment and claim edges.Assignment edges: (the assignment edge means resource is assigned to process , and so on for others)Claim edges: (the claim edge means process is waiting for resource , and so on for others)Which of the following statement(s) is/are CORRECT?
Correct answer
(C) Aborting P₂ makes the system deadlock free.; (D) Aborting P₁ and P₄ makes the system deadlock free.
Solution
To analyze the deadlock, we construct the Wait-for Graph (WFG) where nodes are processes and a directed edge exists if is waiting for a resource held by .Given Edges:
Since resources are single instances, a cycle in the WFG is necessary and sufficient for deadlock.
- Assignment (Held): holds , holds , holds , holds .
- Claim (Waiting):
- waits for (held by )
- waits for (held by )
- waits for (held by )
- waits for (held by )
- waits for (held by )
Since resources are single instances, a cycle in the WFG is necessary and sufficient for deadlock.
1.Cycle 1: (involves )
2.Cycle 2: (involves )
To make the system deadlock-free, we must break all cycles.Analysis of Options:- (A) Aborting : Removes . Breaks Cycle 1. Cycle 2 () remains. Deadlock persists.
- (B) Aborting : Removes . Breaks Cycle 1. Cycle 2 () remains. Deadlock persists.
- (C) Aborting : Removes . Since is part of both Cycle 1 and Cycle 2, removing it breaks both cycles. The system becomes deadlock-free.
- (D) Aborting and :
- Aborting breaks Cycle 1.
- Aborting breaks Cycle 2.
- Both cycles are broken. The system becomes deadlock-free.
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