GATE CS 2008 Q65 — Deadlock

To determine which statement is NOT true, let us analyze the characteristics of deadlock prevention and deadlock avoidance schemes:

• Deadlock Prevention: This approach prevents deadlocks by statically ensuring that at least one of the four necessary conditions for deadlock (Mutual Exclusion, Hold and Wait, No Preemption, Circular Wait) cannot hold. It does not dynamically track safe or unsafe states. Resource requests are granted or denied based on static rules (e.g., ordering of resources), regardless of whether the state is safe. Therefore, Statement A is NOT true.
• Deadlock Avoidance: This approach dynamically decides whether to grant a resource request based on whether the resulting state remains safe (e.g., using the Banker's Algorithm). If the resulting state is safe, the request is granted. Therefore, Statement B is true.
• Restrictiveness: Deadlock prevention is highly restrictive because it imposes strict static constraints on resource requests, which often leads to low resource utilization. Deadlock avoidance is less restrictive because it allows dynamic resource allocation as long as a safe sequence exists. Therefore, Statement C is true.
• A priori Knowledge: Deadlock avoidance algorithms require the system to have prior knowledge of the maximum resource requirements of each process to compute safe states. Therefore, Statement D is true.

Thus, the incorrect statement is A.