2.9 Deadlock & Starvation Explained Simply | OS Concepts | Prevention, Avoidance & Recovery

Описание: Learn Deadlock and Starvation in Operating Systems with simple explanations and real-life examples.
Covers Coffman conditions, prevention, avoidance, detection, recovery, and exam points.

📘 Deadlock – Concept (One-Paragraph Explainer)

A deadlock is a situation in which a group of processes are permanently blocked because each process is holding a resource and waiting for another resource held by some other process. Deadlock occurs due to poor resource allocation and improper synchronization. Once a deadlock happens, no process can proceed on its own. A simple real-life analogy is a four-way traffic junction, where each vehicle blocks the others and no one can move forward. This makes deadlock easy to recognize in exams.

📘 Deadlock Characterization (Coffman Conditions)

Deadlock can occur only if all four Coffman conditions are satisfied simultaneously:
1️⃣ Mutual Exclusion – resources cannot be shared
2️⃣ Hold and Wait – processes hold resources while waiting for others
3️⃣ No Preemption – resources cannot be forcibly taken
4️⃣ Circular Wait – a circular chain of waiting processes exists
📌 Exam Tip: If even one condition is broken, deadlock cannot occur.
Mnemonic: M-H-N-C (Mutual, Hold, No preemption, Circular).

📘 Deadlock Prevention (One-Paragraph Explainer)

Deadlock prevention works by ensuring that at least one Coffman condition never occurs. This is done by changing how resources are requested or allocated, such as forcing processes to request all resources at once or allowing resource preemption. By breaking one condition, deadlock becomes impossible. However, prevention techniques often lead to low resource utilization, reduced concurrency, and inefficiency, making them impractical in many real systems.

📘 Deadlock Avoidance (Short Explainer)

Deadlock avoidance allows the system to dynamically decide whether granting a resource request is safe. The key idea is to keep the system in a safe state, where all processes can complete without deadlock. The Banker’s Algorithm is a classic example used to check system safety before allocation. Unlike prevention, avoidance does not break Coffman conditions but carefully avoids unsafe states.

📘 Deadlock Detection (One-Paragraph Explainer)

Deadlock detection is used in systems where deadlocks are allowed to occur. The operating system periodically checks the system state using deadlock detection algorithms to identify cycles in resource allocation. Once a deadlock is detected, the system takes action to recover. Detection is useful when deadlocks are rare and prevention is too costly.

📘 Deadlock Recovery (Short Explainer)

Deadlock recovery is the process of removing deadlocks after they are detected. Common recovery techniques include terminating one or more processes involved in the deadlock or preempting resources from selected processes. For example, stopping one program can release resources and allow others to continue. Recovery resolves deadlock but may cause loss of work or performance issues.

📘 Starvation (One-Paragraph Explainer)

Starvation occurs when a process waits for a resource indefinitely because other processes keep getting priority. Unlike deadlock, the system continues running, but some processes never get a chance to execute. Starvation often occurs in priority-based scheduling or unfair resource allocation. A key difference is that in starvation, progress is possible, but it is unfairly denied to certain processes.