Table of contents

Introduction

Deadlock is a common problem in Operating Systems that occurs when two or more processes are waiting for each other to release a resource that they are holding, leading to a standstill or an infinite loop. In this article, we’ll dive deep into the topic of deadlock in OS, including what it is, how it happens, and what you can do to prevent it.

1. What is Deadlock?

Deadlock is a state of an OS where two or more processes are stuck in a situation where they can’t proceed further, waiting for a resource that another process is holding. In simpler terms, a deadlock occurs when two or more processes are blocked forever because each is waiting for the other to release a resource.

Deadlock

2. Types of Resources Involved in Deadlocks

Deadlocks can occur with any type of resources that are shared between processes. Some common types of resources that can lead to deadlocks are:

  • CPU cycles
  • Memory
  • Input/output (I/O) devices
  • Files and records
  • Semaphores and mutexes

3. Necessary Conditions for Deadlocks to Occur

Deadlocks can only occur when four necessary conditions are met simultaneously, known as the “four conditions for deadlock.” These conditions are:

  • Mutual Exclusion: A resource can only be used by one process at a time.
  • Hold and Wait: A process holding at least one resource is waiting to acquire additional resources held by other processes.
  • No Preemption: A resource cannot be forcibly taken from a process holding it.
  • Circular Wait: Two or more processes are waiting for each other to release a resource.

4. Examples of Deadlock Scenarios

Some examples of deadlock scenarios in OS are:

  • Two processes, A and B, each holding a resource that the other needs to proceed.
  • Two processes, X and Y, each waiting for a resource that is held by the other process.
  • Multiple processes competing for a limited set of resources.

5. Detection and Prevention of Deadlocks

There are two main approaches to detecting and preventing deadlocks: prevention and avoidance.

Prevention

Prevention involves ensuring that at least one of the necessary conditions for deadlock doesn’t occur. Here are some prevention techniques:

  • Mutual Exclusion: Resources are shared between processes instead of being exclusively held by a single process.
  • Hold and Wait: A process requests all the resources it needs at once, instead of requesting them one by one as it progresses.
  • No Preemption: A process is required to release all resources it is holding before requesting new ones.
  • Circular Wait: Processes are ordered in a way that they can only request resources in a certain order.

Avoidance

Avoidance involves detecting and preventing deadlocks before they occur. This is done by using algorithms that predict whether a resource request will lead to a deadlock or not. Here are some avoidance techniques:

  • Resource Allocation Graph Algorithm: A graphical algorithm that detects deadlocks by constructing a graph that represents the resource allocation and resource requests of processes.
  • Banker’s algorithm: A deadlock avoidance algorithm that prevents deadlocks by making sure that processes can only request resources if they have enough resources to complete their task.

Deadlock Handling Techniques

  1. Deadlock Prevention: As mentioned earlier, this technique involves eliminating at least one of the four necessary conditions for deadlock to occur. It’s the most effective technique, but it’s not always possible to apply in all situations.
  2. Deadlock Avoidance: This technique uses algorithms to detect potential deadlocks before they happen and take corrective actions to avoid them. This technique can be complex and may require significant resources.
  3. Deadlock Recovery: If prevention and avoidance techniques fail, deadlock recovery techniques can be used. The most common technique is to terminate one or more of the processes involved in the deadlock. Another technique is to roll back one or more of the processes to a previously known safe state and restart them. Both of these techniques can be disruptive and may lead to loss of data.

Deadlock Handling Techniques

Deadlock recovery is a technique used to handle a deadlock situation in an operating system. It is used when the prevention and avoidance techniques fail to avoid deadlocks. The goal of deadlock recovery is to break the deadlock and resume normal system operation.

There are several ways to recover from a deadlock. One common technique is to terminate one or more processes involved in the deadlock. By terminating a process, the system can break the circular wait condition and free up resources that were previously held by the deadlocked processes. However, this technique can result in the loss of data or other disruptions.