Question 62

Deadlock prevention operates by invalidating at least one of the four necessary Coffman conditions:

1. Mutual Exclusion
2. Hold and Wait
3. No Preemption
4. Circular Wait

Evaluate the four policies:

• Policy I (Conservative / all-or-nothing): Requesting all resources before execution and releasing all held resources if any is unavailable directly eliminates the Hold-and-Wait condition and allows preemption. It prevents deadlock.
• Policy II (Global Linear Ordering): Numbering resources uniquely and allowing requests only in increasing order prevents Circular Wait, because no cycle can exist in a directed graph where edges always point from lower numbers to higher numbers. It prevents deadlock.
• Policy III (Global Linear Ordering): Allowing requests only in decreasing order also establishes a strict linear ordering, which symmetrically eliminates Circular Wait. It prevents deadlock.
• Policy IV (Monotonic Request Ordering): A process may only request resources strictly greater than any resource it currently holds. This is the standard hierarchical resource ordering policy that eliminates Circular Wait. It prevents deadlock.

Thus, any one of I, II, III, and IV can be used for preventing deadlock (Option D).