Deadlock

Back to Operating Systems
Arjit Sharma
02 Mins

Deadlock occurs when multiple processes get stuck indefinitely, waiting for resources held by each other, preventing further execution. Understanding deadlocks is essential for designing efficient systems and avoiding resource conflicts.

What is a Deadlock?

A deadlock happens when processes:

  • Hold resources that another process needs.
  • Wait for resources held by other waiting processes.

Real-World Example

Imagine two trains approaching an intersection:

  • Each train blocks the track for the other.
  • Neither train can proceed until the other moves, leading to a standstill - this is deadlock in action.

Conditions for Deadlock

Deadlock occurs when all four conditions are present:

1️⃣ Mutual Exclusion – Resources cannot be shared; only one process holds them at a time.

2️⃣ Hold and Wait – A process holding resources requests new ones without releasing the current ones.

3️⃣ No Preemption – Resources cannot be forcibly taken; a process must release them voluntarily.

4️⃣ Circular Wait – A set of processes are waiting for resources held by the next process in the chain, forming a loop.

Deadlock Detection & Prevention

Operating systems use several strategies to detect, prevent, and resolve deadlocks.

1. Deadlock Prevention

Modifies system design so that at least one deadlock condition never occurs:

  • Eliminating Hold and Wait: Ensure processes request all resources upfront before executing.
  • Allowing Preemption: If a resource is locked too long, forcefully remove it from the process and assign it elsewhere.

2. Deadlock Avoidance

Dynamically analyzes resource allocation using algorithms like Banker’s Algorithm, which ensures enough resources remain available for smooth execution.

3. Deadlock Detection & Recovery

Detects deadlocks using resource allocation graphs and resolves them via:

  • Terminating processes involved in the deadlock.
  • Rolling back processes to a safe state before the deadlock occurred.

Conclusion

Deadlock is a critical issue in operating systems, databases, and distributed systems, leading to stalled executions and performance bottlenecks. By applying techniques like prevention, avoidance, and detection, developers and system architects can minimize resource conflicts and enhance system efficiency.

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