Deadlock

Define deadlock and explain the conditions necessary for it to occur.

A set of processes is deadlocked when every process is waiting for an event or resource that only another process in the set can provide. None can proceed or release what the others require.

The source lists four necessary conditions:

1. Mutual exclusion: A resource can be used by only one process at a time.
2. Hold and wait: A process holds resources while waiting for additional resources.
3. No preemption: A resource cannot be forcibly taken away from its owner.
4. Circular wait: There is a circular chain of processes, each waiting for a resource held by the next.

All four must hold for deadlock to occur; breaking a necessary condition prevents it. Original process notation and discussion:

For m identical resources and n processes, each requesting one resource at a time, prove the no-deadlock result under the maximum-demand conditions stated in the source.

The question bounds each process's maximum need between 1 and m and gives an inequality involving the sum of maximum needs and m + n. The original statement and proof are reproduced as images so that all inequalities, summations, and handwritten steps remain unchanged.

The handwritten algebra is not independently validated. Read the original conditions and steps together; this conversion does not repair the proof.

For five processes and resource totals A = 7, B = 2, C = 6, use the supplied allocation/request tables to determine whether the state is deadlocked and whether P2's additional request (0, 0, 1) can be granted.

The source constructs allocation, request/need, and work tables. It claims the system is not deadlocked and gives the order P0, P2, P3, P4, P1. It rejects the additional request with an available vector of (0, 0, 0).

Source inconsistency: The working treats a request table as a maximum-demand table and contains negative need entries. The reported conclusion is retained for fidelity and is not a validated Banker/detection result.

The full original matrices and working follow:

State the necessary conditions for deadlock and explain detection and recovery.

The four conditions are given in Question 1. With one instance of each resource type, a cycle in the wait-for graph identifies deadlock. For multiple instances, the source describes a matrix-based detection approach examining requests, allocations, and available resources.

Recovery approaches include:

• Preemption: Take a resource from a process when that resource supports it.
• Rollback: Restore a process to a saved checkpoint so resources can be released.
• Termination: Kill a process, choosing one whose termination has a comparatively small impact, to break the deadlock.

Original graphs and recovery discussion:

Define deadlock, state its necessary conditions, and explain detection with examples.

Cross-references the earlier definition/conditions and detection answers. See Question 1 and Question 4, including the original diagrams.

Explain deadlock avoidance, detection, and prevention.

Avoidance checks a request before granting it and permits allocation only if the resulting state remains safe. Detection checks whether deadlock has occurred when it is not prevented in advance. Prevention denies at least one of the four necessary conditions.

The source discusses requiring a process to obtain all resources before starting, with the disadvantage of low utilization; preemption; and restricting resource acquisition to break circular waiting. Mutual exclusion appears as a listed condition without a separate prevention explanation.

The circular-wait paragraph contains a repeated resource label that makes its release rule unclear. Its wording is retained in the scan rather than silently corrected.

Differentiate deadlock from indefinite postponement. For five processes and four resource types with totals (6, 4, 4, 2), use the supplied allocation and maximum-demand matrices to examine safety.

In deadlock, processes cannot progress because each needs an event or resource another blocked process must provide. With indefinite postponement, a process could in principle run but is repeatedly delayed.

The source computes an available vector of (1, 1, 2, 0) and gives the safe sequence P2, P3, P4, P0, P1. The original matrices, need calculations, and work-vector updates are retained below without substituting a new calculation:

A separate question statement is not available for this exam heading.

This exam heading appears without a separate complete question and answer. The preceding worked safety example is retained in Question 7; no new problem has been invented for this heading.

Two processes share three resources, and each needs at most two. Can the system deadlock? Explain using the deadlock conditions.

The source reviews the four conditions and illustrates assigning two resources to one process and one to the other. The first process can finish and release its resources so the second can complete; the source concludes that the illustrated system does not deadlock.

The source uses the word “preempt” in its explanation of resources becoming available after completion. The drawing and original wording remain unchanged below.

Repeated safety question — 2075 Bhadra.

The handwritten entry says the question is similar to 2073 Bhadra. See Question 7. A separate statement and worked solution are not supplied.