Deadlock: processes wait forever for each others resources

Introduction

In operating systems, a deadlock is like a traffic jam where every car 🚗 waits for another to move, but no one ever does! 😵 Multiple processes get stuck, each waiting for resources held by others. This freeze 🧊 can crash performance if not handled. ⚠️

Deadlock in OS

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1. 🔄 What is Deadlock?

• A situation where processes get stuck, each waiting for a resource held by another. No one can proceed.

2. 🧩 Necessary Conditions

• Mutual Exclusion
• Hold and Wait
• No Preemption
• Circular Wait

3. 🔍 Deadlock Detection

• The system checks for cycles in resource allocation to spot deadlocks.

4. 🛡️ Deadlock Prevention

• Ensure at least one of the necessary conditions doesn’t hold.

5. 🚦 Deadlock Avoidance

• Use algorithms like Banker’s Algorithm to avoid unsafe states.

6. 🔁 Deadlock Recovery

• Choose a victim process and terminate or roll back to break the deadlock.

7. ⚖️ Deadlock vs Starvation

• Deadlock: processes wait forever.
• Starvation: some processes may never get resources due to others' priority.

8. ✅ Pros & Cons

• Helps understand system behavior.
• Can reduce performance and cause system hangs.

9. 🔚 Conclusion

• Proper handling is crucial to maintain system reliability and performance.

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Necessary Conditions for Deadlock

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Deadlock Detection

Deadlock Prevention Techniques

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1. Mutual Exclusion

• What it means: A resource can be used by only one process at a time.
• How to prevent: Try to make resources shareable.
• Problem: Not possible for all resources (like printers).

2. Hold and Wait

• What it means: A process holds one resource and waits for more.
• How to prevent:
• Ask all needed resources at once.
• Or release held resources before asking for new ones.
• Problem: Wastes resources and causes delays.

3. No Preemption

• What it means: Resources can't be taken from a process.
• How to prevent: Allow taking back resources if needed.
• Problem: Not always safe or possible for some resources.

4. Circular Wait

• What it means: A cycle where each process waits for a resource held by the next.
• How to prevent:
• Set a fixed order to request resources.
• Processes must request in that order.
• Problem: Makes system less flexible.

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Deadlock Avoidance Techniques

Deadlock Recovery Methods

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Deadlock Handling Strategies

1. 🔍 Deadlock Detection and Recovery

• Let the system enter deadlock, then detect and recover.
• Suitable when deadlocks are rare.

2. 🛑 Deadlock Prevention

• Design system to avoid one or more necessary conditions for deadlock.
• Example: don’t allow hold and wait.

3. 🛡️ Deadlock Avoidance

• System checks in advance if a request might lead to deadlock.
• Uses techniques like Banker's Algorithm.

4. 🚫 Ignore the Problem (Ostrich Approach)

• Assume deadlock won’t happen; don’t handle it.
• Used in systems where deadlocks are very rare (e.g., some UNIX systems).

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Difference Between Deadlock and Starvation

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Starvation: Causes and Solutions

⚠️ Causes of Starvation

1. 🔁 Biased Scheduling Algorithms

• Some algorithms favor high-priority processes.
• Low-priority processes may never get a chance to execute.

2. 🔝 Continuous Arrival of High-Priority Tasks

• If the system always receives high-priority tasks, lower-priority ones get pushed back indefinitely.

3. 🔒 Resource Locking

• When resources are always occupied by other processes, some may keep waiting.

4. 🚫 No Aging Mechanism

• Without increasing the priority of waiting processes over time, they may starve.

5. 🔄 Improper Resource Allocation

• Resource allocation not considering fairness can cause repeated denial of access.

✅ Solutions to Starvation

1. ⏫ Aging Technique

• Gradually increase the priority of waiting processes to ensure they eventually get CPU time.

2. ⚖️ Fair Scheduling Algorithms

• Use fair schedulers like Round Robin or Fair Share Scheduling to distribute CPU evenly.

3. ⛔ Limit Priority Inversion

• Prevent high-priority tasks from blocking lower ones forever by using priority inheritance.

4. 🧠 Smart Resource Allocation Policies

• Design resource handling with fairness and guaranteed access in mind.

5. 📊 Monitoring & Feedback Systems

• Regularly monitor system behavior and adjust priorities or resource distribution dynamically.

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Advantages and Disadvantages of Deadlock Handling

Conclusion

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1. Nature of Deadlock

• Deadlock occurs when processes are indefinitely waiting for resources held by each other.
• It leads to system freeze and poor resource utilization.

2. Need for Handling

• Ignoring deadlocks can result in degraded system performance and user dissatisfaction.
• Efficient handling is necessary in critical and real-time systems.

3. Strategies Available

• Prevention: Design system to eliminate one or more necessary conditions for deadlock.
• Avoidance: Use algorithms like Banker's Algorithm to stay in safe states.
• Detection and Recovery: Allow deadlocks but detect and recover when they occur.
• Ignore (Ostrich Method): Used where deadlocks are rare and minimal impact is expected.

4. Choosing the Right Approach

• Depends on system type, application requirements, and expected deadlock frequency.
• Balance between performance, complexity, and safety is crucial.

5. Overall Importance

• Mastery of deadlock concepts helps in designing better operating systems.
• Ensures system reliability, efficiency, and optimal resource use.

FAQs

Q.1. What is a deadlock in operating systems?
A : A deadlock is a situation where two or more processes are stuck waiting for each other’s resources, and none can proceed.

Q.2. What causes a deadlock?
Deadlocks occur when the following four conditions hold simultaneously:
A : Mutual Exclusion
A: Hold and Wait
A : No Preemption
A : Circular Wait

Q.3. How is deadlock different from starvation?
A : In deadlock, all involved processes are blocked indefinitely.
A : In starvation, a process waits too long due to low priority but others may continue.

Q.4. Can deadlocks be prevented?
A : Yes. Deadlocks can be prevented by breaking one of the four necessary conditions using system design strategies.

Q.5. What is deadlock detection?
A : Deadlock detection involves monitoring resource allocation to identify cycles or blockages, and then taking steps to resolve them.

Q.6. What is the Banker's Algorithm?
A : Its a deadlock avoidance algorithm that allocates resources only if the system remains in a safe state after allocation.

Q.7. What are some ways to recover from a deadlock?
A : Terminate one or more processes.
A : Rollback a process to a safe state.
A : Preempt resources and assign them elsewhere.

Q.8. Is deadlock handling always necessary?
A : Not always. In some systems where deadlocks are rare or have low impact, developers may choose to ignore them.

Q.9. Can deadlocks happen in real life?
A : Yes. Deadlocks can occur in database systems, network traffic, and even daily scenarios like two people holding doors waiting for each other.

Q.10. Why is deadlock a problem?
A : Deadlocks waste system resources, reduce performance, and can cause system crashes if not resolved.