The 4 conditions for deadlocks

PublishedJanuary 11, 2024

I am Jyotiprakash, a deeply driven computer systems engineer, software developer, teacher, and philosopher. With a decade of professional experience, I have contributed to various cutting-edge software products in network security, mobile apps, and healthcare software at renowned companies like Oracle, Yahoo, and Epic. My academic journey has taken me to prestigious institutions such as the University of Wisconsin-Madison and BITS Pilani in India, where I consistently ranked among the top of my class.

At my core, I am a computer enthusiast with a profound interest in understanding the intricacies of computer programming. My skills are not limited to application programming in Java; I have also delved deeply into computer hardware, learning about various architectures, low-level assembly programming, Linux kernel implementation, and writing device drivers. The contributions of Linus Torvalds, Ken Thompson, and Dennis Ritchie—who revolutionized the computer industry—inspire me. I believe that real contributions to computer science are made by mastering all levels of abstraction and understanding systems inside out.

In addition to my professional pursuits, I am passionate about teaching and sharing knowledge. I have spent two years as a teaching assistant at UW Madison, where I taught complex concepts in operating systems, computer graphics, and data structures to both graduate and undergraduate students. Currently, I am an assistant professor at KIIT, Bhubaneswar, where I continue to teach computer science to undergraduate and graduate students. I am also working on writing a few free books on systems programming, as I believe in freely sharing knowledge to empower others.

Comments

Join the discussion

No comments yet. Be the first to comment.

More from this blog

Computer Arithmetic: From Fast Adders to Floating-Point

Arithmetic is the beating heart of every processor. Whether your machine is rendering 3-D graphics, training a neural network, or simply incrementing a loop counter, the ALU (Arithmetic Logic Unit) is doing the heavy lifting. In this deep-dive, I wan...

Feb 12, 202629 min read

The Complete Memory Hierarchy: From Semiconductor RAM to Virtual Memory

The performance gap between processors and main memory has been widening for decades. Modern processors can execute billions of instructions per second, but accessing data from main memory takes hundreds of processor cycles. This disparity creates a ...

Jan 7, 202670 min read

The Ultimate Spring Boot Guide: From Fundamentals to Production-Ready REST APIs

Introduction Welcome to the most comprehensive Spring Boot guide you'll find! This isn't just another tutorial that skims the surface. We're going to dive deep into every concept, explain every annotation, walk through every line of code, and underst...

Dec 26, 2025125 min read

Understanding Functions, Memory, and Pointers in C: A Complete Guide

Part 1: Functions and the Call Stack Before we can understand pointers and memory management in C, we need to understand how functions work and what happens behind the scenes when your program runs. This foundation will make everything else click int...

Dec 16, 202583 min read

Datapath and Control

The Basic Processing Unit is the brain of every computer. It fetches instructions from memory, decodes them, and executes the operations they specify. Whether you're running a simple addition or a complex algorithm, every operation flows through this...

Dec 10, 202534 min read

Jyotiprakash's Blog

251 posts

I'm Jyotiprakash, a software dev and professor at KIIT, with expertise in system programming.

Deadlocks occur when four necessary conditions hold simultaneously. These conditions, known as the "Four Conditions for Deadlock," are:

Mutual Exclusion:
- This condition means that at least one resource must be non-sharable, meaning only one process can use it at a time.
- Examples include printers, processors, or hardware devices that can only be used by one process at a time.
- For instance, consider a printer that can print only one document at a time. If Process A is printing a document, Process B must wait until Process A completes its printing job.
Hold and Wait:
- This condition implies that processes hold resources while waiting for others.
- A process that has already acquired some resources may request additional resources without releasing the ones it already holds.
- For example, suppose Process A holds Resource 1 and needs Resource 2 while Process B holds Resource 2 and needs Resource 1. Both processes are waiting for the resource the other holds, leading to a deadlock.
No Preemption:
- Preemption means forcibly taking resources from a process.
- This condition states that resources cannot be forcibly taken away from a process; they must be released voluntarily.
- Consider a scenario where Process A holds Resource 1, and Process B needs it. If preemption were allowed, the system could forcibly take Resource 1 from Process A and give it to Process B to resolve the deadlock. However, the "no preemption" condition prevents this.
Circular Wait:
- This condition means there exists a circular chain of processes, each of which is waiting for a resource held by the next process in the chain.
- For instance, if Process A is waiting for a resource held by Process B, Process B is waiting for a resource held by Process C, and so on, with Process Z waiting for a resource held by Process A, a circular wait exists.
- Circular wait can be illustrated using a graph where processes are nodes, and edges represent resources. In a deadlock, this graph contains a cycle.

Detailed Examples:

Let's use a computer science example to illustrate these conditions:

Suppose we have two processes, Process A and Process B, and two resources, Resource 1 and Resource 2, which they need to complete their tasks.

Mutual Exclusion: Consider a case where both Process A and Process B require exclusive access to a printer. Since a printer can only be used by one process at a time, this condition is met.
Hold and Wait: Now, imagine that Process A has acquired the printer (Resource 1) but also needs access to a scanner (Resource 2). Instead of releasing the printer, it keeps it while waiting for the scanner to become available. Meanwhile, Process B needs the scanner but is holding onto the printer while waiting. Both processes are holding resources while waiting for others.
No Preemption: In this scenario, we assume that the operating system does not allow preemption of resources. It cannot forcibly take the printer from Process A and give it to Process B without violating the "no preemption" condition.
Circular Wait: If we represent the situation as a graph, we see that there is a circular chain. Process A is waiting for Resource 2 (held by Process B), and Process B is waiting for Resource 1 (held by Process A). This circular dependency fulfills the "circular wait" condition.

As all four conditions hold simultaneously in this example, a deadlock is possible. Both processes are stuck and cannot proceed, resulting in a deadlock situation. To resolve it, one or more of these conditions must be broken, such as allowing preemption or ensuring that processes release resources when they cannot get the ones they need.

Command Palette

Comments

More from this blog