Resource allocation graph in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Resource Allocation Graph Components

In a resource allocation graph, what does a directed edge from a process node to a resource node represent?

A The resource is being released by the process.

B The process is currently holding the resource.

C The resource is free and available.

D The process is requesting the resource.

💡 Hint

Think about what it means when a process points to a resource in the graph.

A directed edge from a process to a resource means the process is requesting that resource. Conversely, an edge from a resource to a process means the resource is allocated to that process.

📋 Factual

intermediate

Deadlock Detection Using Resource Allocation Graph

Which condition in a resource allocation graph indicates a deadlock?

A Presence of a cycle in the graph.

B No edges in the graph.

C All resources are free.

D Only one process is in the graph.

💡 Hint

Deadlock happens when processes wait indefinitely. What does a cycle represent?

A cycle in the resource allocation graph means a set of processes are waiting for resources held by each other, causing deadlock.

🔍 Analysis

advanced

Interpreting a Resource Allocation Graph Scenario

Given a resource allocation graph where process P1 holds resource R1 and requests resource R2, while process P2 holds resource R2 and requests resource R1, what does this situation represent?

A Deadlock; both processes are waiting indefinitely.

B No deadlock; both processes will complete.

C Starvation of P1 only.

D Resource R1 is free.

💡 Hint

Consider if the processes can proceed or are stuck waiting for each other.

Each process holds a resource the other needs and waits for the other's resource, forming a cycle and causing deadlock.

❓ Comparison

advanced

Difference Between Resource Allocation Graph and Wait-For Graph

Which statement correctly distinguishes a resource allocation graph from a wait-for graph?

A Both graphs are identical in structure and purpose.

B Wait-for graph includes resources; resource allocation graph does not.

C Resource allocation graph shows processes and resources; wait-for graph shows only processes and their waiting relationships.

D Resource allocation graph shows only processes; wait-for graph shows only resources.

💡 Hint

Think about what nodes each graph contains.

A resource allocation graph includes both processes and resources as nodes, while a wait-for graph simplifies this by showing only processes and edges representing waiting relationships.

❓ Reasoning

expert

Determining the Number of Edges in a Resource Allocation Graph

Consider a system with 3 processes (P1, P2, P3) and 2 resources (R1, R2). P1 holds R1 and requests R2, P2 holds R2 and requests R1, and P3 requests R2 but holds no resources. How many edges are in the resource allocation graph?

A 4 edges

B 5 edges

C 6 edges

D 3 edges

💡 Hint

Count edges from processes to resources (requests) and from resources to processes (allocations).

Edges: P1 → R2 (request), R1 → P1 (allocation), P2 → R1 (request), R2 → P2 (allocation), P3 → R2 (request). Total 5 edges.

Practice

1. What does a resource allocation graph primarily represent in an operating system?

easy

A. The network connections between computers

B. The file system hierarchy of the operating system

C. The relationship between processes and the resources they hold or request

D. The CPU scheduling order of processes

Solution

1. Step 1: Understand the purpose of resource allocation graphs

   Resource allocation graphs show which processes hold resources and which are waiting for them.

2. Step 2: Compare with other options

   File systems, network connections, and CPU scheduling are unrelated to resource allocation graphs.

3. Final Answer:

   The relationship between processes and the resources they hold or request -> Option C

4. Quick Check:

   Resource allocation graph = process-resource relationships [OK]

Hint: Focus on process-resource connections, not unrelated system parts [OK]

Common Mistakes:

• Confusing resource allocation graph with file system structure
• Thinking it shows network or CPU scheduling details

2. Which of the following correctly represents an edge from a process to a resource in a resource allocation graph?

easy

A. An arrow from the process node to the resource node

B. An arrow from the resource node to the process node

C. A double-headed arrow between process and resource nodes

D. No arrow, just a line connecting process and resource

Solution

1. Step 1: Recall edge direction meanings

   An arrow from a process to a resource means the process is requesting that resource.

2. Step 2: Eliminate incorrect options

   Arrow from resource to process means resource is allocated; double-headed or no arrow are incorrect representations.

3. Final Answer:

   An arrow from the process node to the resource node -> Option A

4. Quick Check:

   Process to resource = request edge [OK]

Hint: Process to resource arrow means request; resource to process means allocation [OK]

Common Mistakes:

• Reversing arrow directions for request and allocation
• Assuming no arrows are used

3. Consider a resource allocation graph with processes P1, P2 and resources R1, R2. P1 holds R1 and requests R2. P2 holds R2 and requests R1. What does this graph indicate?

medium

A. Deadlock exists between P1 and P2

B. Only P2 is deadlocked

C. Only P1 is deadlocked

D. No deadlock, processes can proceed

Solution

1. Step 1: Identify the cycle in the graph

   P1 holds R1 and waits for R2; P2 holds R2 and waits for R1, forming a cycle.

2. Step 2: Understand cycle implication

   A cycle in a resource allocation graph means deadlock among involved processes.

3. Final Answer:

   Deadlock exists between P1 and P2 -> Option A

4. Quick Check:

   Cycle in graph = deadlock [OK]

Hint: Look for cycles to detect deadlocks quickly [OK]

Common Mistakes:

• Ignoring the cycle and assuming no deadlock
• Thinking only one process is deadlocked

4. A resource allocation graph shows a cycle involving three processes and three resources. Which of the following fixes the deadlock?

medium

A. Remove all edges from resources to processes

B. Remove one edge from a process to a resource in the cycle

C. Add more edges to connect all processes

D. Ignore the cycle; it will resolve automatically

Solution

1. Step 1: Understand deadlock resolution in resource allocation graphs

   Removing an edge in the cycle breaks the cycle and resolves deadlock.

2. Step 2: Evaluate other options

   Adding edges or removing all edges from resources to processes does not fix deadlock; ignoring it is unsafe.

3. Final Answer:

   Remove one edge from a process to a resource in the cycle -> Option B

4. Quick Check:

   Break cycle by removing an edge [OK]

Hint: Break cycles by removing one request edge [OK]

Common Mistakes:

• Adding edges instead of removing
• Ignoring deadlock cycles

5. In a system with multiple processes and resources, how can a resource allocation graph help the operating system avoid deadlocks?

hard

A. By ignoring resource requests to reduce complexity

B. By increasing CPU speed to finish processes faster

C. By randomly killing processes to free resources

D. By detecting cycles early and preventing resource allocation that causes them

Solution

1. Step 1: Understand the role of resource allocation graphs

   They help detect cycles that indicate deadlocks before they happen.

2. Step 2: How OS uses this information

   The OS can prevent granting resource requests that would create cycles, thus avoiding deadlocks.

3. Final Answer:

   By detecting cycles early and preventing resource allocation that causes them -> Option D

4. Quick Check:

   Cycle detection prevents deadlocks [OK]

Hint: Prevent cycles by denying risky resource requests [OK]

Common Mistakes:

• Thinking CPU speed affects deadlocks
• Assuming random process termination is a solution
• Ignoring resource requests is not practical