The document discusses deadlocks in operating systems. It begins by providing examples of deadlock situations and defining the four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. It then describes methods for handling deadlocks, including deadlock prevention, avoidance, detection, and recovery. For prevention and avoidance, it discusses specific algorithms like the banking algorithm and resource allocation graphs. The document provides examples and diagrams to illustrate deadlock states and algorithms.
This document discusses deadlocks in computer systems. It begins by defining a deadlock as a state where a set of blocked processes are each holding resources and waiting for resources held by others in a cyclic manner. It then presents methods for handling deadlocks, including prevention, avoidance, and detection and recovery. For avoidance, it describes using a resource allocation graph to model processes and resources, and the banker's algorithm to ensure the system is always in a safe state where deadlocks cannot occur.
Deadlock Detection in Distributed SystemsDHIVYADEVAKI
The document discusses deadlocks in computing systems. It defines deadlocks and related concepts like livelock and starvation. It presents various approaches to deal with deadlocks including detection and recovery, avoidance through runtime checks, and prevention by restricting resource requests. Graph-based algorithms are described for detecting and preventing deadlocks by analyzing resource allocation graphs. The Banker's algorithm is introduced as a static prevention method. Finally, it discusses ways to eliminate the conditions required for deadlocks, like mutual exclusion, hold-and-wait, and circular wait.
A document about deadlocks in operating systems is summarized as follows:
1. A deadlock occurs when a set of processes form a circular chain where each process is waiting for a resource held by the next process in the chain. The four conditions for deadlock are mutual exclusion, hold and wait, no preemption, and circular wait.
2. Deadlocks can be modeled using a resource allocation graph where processes and resources are vertices and edges represent resource requests. A cycle in the graph indicates a potential deadlock.
3. Methods for handling deadlocks include prevention, avoidance, and detection/recovery. Prevention ensures deadlock conditions cannot occur while avoidance allows the system to dynamically verify new allocations will not
The document discusses different methods for handling deadlocks in a system. It describes deadlock characterization including the necessary conditions for deadlock, using a resource-allocation graph to model deadlocks, and examples of such graphs. It also explains several methods for handling deadlocks including deadlock prevention, avoidance, and detection and recovery. Deadlock prevention methods aim to enforce constraints to ensure the necessary conditions for deadlock cannot occur. Deadlock avoidance uses additional information to dynamically monitor the system state and ensure it remains in a safe state where deadlocks cannot happen.
The document discusses deadlocks in computer systems and various approaches to handling them. It defines deadlock as when a set of processes are blocked waiting for resources held by each other in a cyclic manner. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include ignoring the problem, preventing deadlocks through design restrictions, avoiding deadlocks by dynamically checking for safety, and detecting and recovering from deadlocks after the fact. The banker's algorithm is presented as an avoidance technique using a resource allocation graph and safety checks.
The document discusses deadlocks in computer systems. It defines deadlock, presents examples, and describes four conditions required for deadlock to occur. Several methods for handling deadlocks are discussed, including prevention, avoidance, detection, and recovery. Prevention methods aim to ensure deadlocks never occur, while avoidance allows the system to dynamically prevent unsafe states. Detection identifies when the system is in a deadlocked state.
Deadlock- System model, resource types, deadlock problem, deadlock characteri...Wakil Kumar
Help to other students on research paper on Deadlock- System model, resource types, deadlock problem, deadlock characterization, methods for deadlock handling,
This document discusses deadlocks in computer systems. It begins by defining a deadlock as a state where a set of blocked processes are each holding resources and waiting for resources held by others in a cyclic manner. It then presents methods for handling deadlocks, including prevention, avoidance, and detection and recovery. For avoidance, it describes using a resource allocation graph to model processes and resources, and the banker's algorithm to ensure the system is always in a safe state where deadlocks cannot occur.
Deadlock Detection in Distributed SystemsDHIVYADEVAKI
The document discusses deadlocks in computing systems. It defines deadlocks and related concepts like livelock and starvation. It presents various approaches to deal with deadlocks including detection and recovery, avoidance through runtime checks, and prevention by restricting resource requests. Graph-based algorithms are described for detecting and preventing deadlocks by analyzing resource allocation graphs. The Banker's algorithm is introduced as a static prevention method. Finally, it discusses ways to eliminate the conditions required for deadlocks, like mutual exclusion, hold-and-wait, and circular wait.
A document about deadlocks in operating systems is summarized as follows:
1. A deadlock occurs when a set of processes form a circular chain where each process is waiting for a resource held by the next process in the chain. The four conditions for deadlock are mutual exclusion, hold and wait, no preemption, and circular wait.
2. Deadlocks can be modeled using a resource allocation graph where processes and resources are vertices and edges represent resource requests. A cycle in the graph indicates a potential deadlock.
3. Methods for handling deadlocks include prevention, avoidance, and detection/recovery. Prevention ensures deadlock conditions cannot occur while avoidance allows the system to dynamically verify new allocations will not
The document discusses different methods for handling deadlocks in a system. It describes deadlock characterization including the necessary conditions for deadlock, using a resource-allocation graph to model deadlocks, and examples of such graphs. It also explains several methods for handling deadlocks including deadlock prevention, avoidance, and detection and recovery. Deadlock prevention methods aim to enforce constraints to ensure the necessary conditions for deadlock cannot occur. Deadlock avoidance uses additional information to dynamically monitor the system state and ensure it remains in a safe state where deadlocks cannot happen.
The document discusses deadlocks in computer systems and various approaches to handling them. It defines deadlock as when a set of processes are blocked waiting for resources held by each other in a cyclic manner. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include ignoring the problem, preventing deadlocks through design restrictions, avoiding deadlocks by dynamically checking for safety, and detecting and recovering from deadlocks after the fact. The banker's algorithm is presented as an avoidance technique using a resource allocation graph and safety checks.
The document discusses deadlocks in computer systems. It defines deadlock, presents examples, and describes four conditions required for deadlock to occur. Several methods for handling deadlocks are discussed, including prevention, avoidance, detection, and recovery. Prevention methods aim to ensure deadlocks never occur, while avoidance allows the system to dynamically prevent unsafe states. Detection identifies when the system is in a deadlocked state.
Deadlock- System model, resource types, deadlock problem, deadlock characteri...Wakil Kumar
Help to other students on research paper on Deadlock- System model, resource types, deadlock problem, deadlock characterization, methods for deadlock handling,
This document discusses operating system topics related to deadlocks, including definitions, properties, prevention, detection, and recovery from deadlocks. It defines deadlock as when a process requests resources that are held by another waiting process, creating a circular wait. Four conditions must be met for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Techniques to prevent deadlocks include deadlock avoidance using safe states and resource allocation graphs, and deadlock prevention by ensuring one of the four conditions is never satisfied. Deadlock detection uses wait-for graphs or detection algorithms, and recovery options are terminating processes or preempting resources.
The document discusses deadlocks in operating systems. It defines deadlock as when a process waits for a resource held by another waiting process, forming a circular chain of processes waiting for each other. It characterizes deadlock by the conditions of mutual exclusion, hold and wait, no preemption, and circular wait. The document outlines strategies to handle deadlocks through prevention, avoidance, and detection and recovery. It describes resource allocation graphs to model deadlocks and the conditions for deadlocks using AND and OR resource allocation. Finally, it discusses different techniques for deadlock prevention, detection, and recovery in a system.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
Deadlock and memory management -- Operating SystemEktaVaswani2
This document discusses operating system resources, deadlocks, and memory management. It defines system resources as any usable parts of a computer that can be controlled and assigned by the operating system. It describes the four conditions required for a deadlock and methods for detecting, avoiding, and recovering from deadlocks such as terminating processes. It also discusses memory management techniques like paging, swapping, and virtual memory that allow more programs to reside in memory than the physical memory size.
This document describes a course on operating systems with a focus on deadlocks and memory management. It discusses deadlocks in depth, including the necessary conditions for deadlocks, methods for handling them through prevention, avoidance, detection and recovery. For deadlock prevention, it describes how to ensure the hold-and-wait, no preemption and circular wait conditions do not occur. Deadlock avoidance requires knowledge of future resource requests to determine if a process must wait. The document also provides an overview of memory management strategies like swapping, contiguous allocation and paging.
The document discusses deadlock in computer systems. It defines deadlock and lists necessary conditions for deadlock including mutual exclusion, hold and wait, no preemption, and circular wait. It also discusses strategies for dealing with deadlock such as detection, recovery, and prevention/avoidance. The resource allocation graph (RAG) model is introduced as a way to represent system states and detect deadlock. Algorithms like Banker's algorithm aim to avoid deadlock by ensuring safe allocation of resources.
Deadlocks occur when a set of blocked processes each hold resources and wait for resources held by other processes in the set, resulting in a circular wait. The four necessary conditions for deadlock are: mutual exclusion, hold and wait, no preemption, and circular wait. The banker's algorithm is a deadlock avoidance technique that requires processes to declare maximum resource needs upfront. It ensures the system is always in a safe state by delaying resource requests that could lead to an unsafe state where deadlock is possible.
This document discusses deadlocks in operating systems. It defines deadlock as when a set of blocked processes each hold a resource and wait for a resource held by another process. It then covers methods for handling deadlocks such as prevention, avoidance, detection, and recovery. Prevention ensures deadlock conditions cannot occur. Avoidance allows the system to deny requests that could lead to deadlock. Detection identifies when a deadlock has occurred. Recovery breaks deadlocks by terminating or preempting processes.
This document discusses deadlocks and techniques for handling them. It begins by defining the four necessary conditions for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It then describes three approaches to handling deadlocks: prevention, avoidance, and detection and recovery. Prevention aims to ensure one of the four conditions never holds. Avoidance uses more information to determine if a request could lead to a deadlock. Detection and recovery allows deadlocks but detects and recovers from them after the fact. The document provides examples of different prevention techniques like limiting resource types that can be held, ordering resource types, and preemption. It also explains the banker's algorithm for deadlock avoidance.
This document discusses deadlock avoidance techniques. It explains the concepts of safe and unsafe states when allocating resources to processes. The resource allocation graph algorithm uses claim and assignment edges to model potential resource requests. Banker's algorithm requires processes to declare maximum resource needs upfront. It uses an allocation matrix and need matrix to determine if allocating resources to a process will result in an unsafe state. An example demonstrates tracking available resources and determining if processes can safely obtain requested resources without causing deadlock.
This document discusses deadlock in computer systems. It defines deadlock as when a set of processes are blocked waiting for resources held by other processes in the set. Four necessary conditions for deadlock to occur are outlined: mutual exclusion, hold and wait, no preemption, and circular wait. Strategies to handle deadlock such as prevention, detection, avoidance, and an integrated approach combining multiple strategies are also discussed. Examples of different resource types that can be involved in deadlock are provided.
This document discusses various approaches to handling deadlocks in operating systems, including deadlock prevention, avoidance, detection, and recovery. It describes the four necessary conditions for deadlock, and models the problem using resource allocation graphs. Prevention methods aim to enforce constraints to ensure deadlock cannot occur, while avoidance algorithms dynamically monitor the system state to guarantee safety. Detection algorithms periodically search allocation graphs or wait-for graphs to find cycles indicating deadlock. Recovery requires rolling back processes to free locked resources.
The document summarizes different approaches to handling deadlocks in operating systems, including prevention, avoidance, detection, and recovery. It describes the four conditions required for deadlock, and models for representing resource allocation and processes waiting for resources, such as resource allocation graphs and wait-for graphs. Detection algorithms allow the system to enter a deadlocked state and then identify cycles in wait-for graphs to detect deadlocks.
This document summarizes key concepts related to deadlock avoidance in operating systems. It discusses the four conditions for deadlock, describes the concept of a safe state for resource allocation, and provides an example of modeling resource allocation using a resource allocation graph. The document is presented as part of a course on operating systems, covering topics such as deadlock avoidance, safe state determination, and modeling resource allocation through graphs.
There are three main approaches to handling deadlocks: prevention, avoidance, and detection with recovery. Prevention methods constrain how processes request resources to ensure at least one necessary condition for deadlock cannot occur. Avoidance requires advance knowledge of processes' resource needs to decide if requests can be immediately satisfied. Detection identifies when a deadlocked state occurs and recovers by undoing the allocation that caused it.
Deadlocks can be addressed through four main strategies: detection and recovery, avoidance, and prevention. Prevention ensures that at least one of the four conditions for deadlock never occurs, such as by assigning a numeric order to resources and requiring processes request them in that order to avoid circular waits.
This document summarizes a chapter on deadlocks from an operating systems textbook. It defines deadlock as when a set of blocked processes wait for resources held by each other. Four conditions must be met for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include prevention, avoidance, detection, and recovery. Prevention ensures deadlocks cannot occur by restricting resource usage. Avoidance dynamically checks the system state remains safe to prevent deadlocks. Detection allows deadlocks but recovers the system. Recovery options are terminating processes or preempting resources.
The implementation of Banker's algorithm, data structure and its parserMatthew Chang
The document summarizes a student project presentation on implementing Banker's algorithm for deadlock avoidance. It includes:
1) An overview of Banker's algorithm and how it checks for safe states to avoid deadlock by dynamically evaluating resource requests.
2) Details on the data structures and parsing approach used to represent the banker's algorithm information and process resource requests.
3) A demonstration of the program loading sample data from a file, displaying the banker's algorithm information, and handling different user commands and error scenarios.
The document discusses deadlocks in operating systems. It defines deadlock as a situation where a set of processes are blocked waiting for resources held by other processes in the set, resulting in none of the processes making any progress. Four conditions must be met for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. The document presents examples to illustrate deadlock and discusses different strategies for dealing with it, including deadlock prevention, avoidance, and detection and recovery. It specifically describes the Banker's Algorithm for deadlock avoidance.
This document discusses deadlocks, including the four conditions required for a deadlock, methods to avoid deadlocks like using safe states and Banker's Algorithm, ways to detect deadlocks using wait-for graphs and detection algorithms, and approaches to recover from deadlocks such as terminating processes or preempting resources.
This document discusses deadlocks in operating systems. It defines a deadlock as a set of blocked processes that are each holding a resource and waiting for a resource held by another process. Four conditions must be met for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlocks can be modeled using directed resource allocation graphs. Methods for handling deadlocks include prevention, avoidance, detection, and recovery.
This document discusses operating system topics related to deadlocks, including definitions, properties, prevention, detection, and recovery from deadlocks. It defines deadlock as when a process requests resources that are held by another waiting process, creating a circular wait. Four conditions must be met for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Techniques to prevent deadlocks include deadlock avoidance using safe states and resource allocation graphs, and deadlock prevention by ensuring one of the four conditions is never satisfied. Deadlock detection uses wait-for graphs or detection algorithms, and recovery options are terminating processes or preempting resources.
The document discusses deadlocks in operating systems. It defines deadlock as when a process waits for a resource held by another waiting process, forming a circular chain of processes waiting for each other. It characterizes deadlock by the conditions of mutual exclusion, hold and wait, no preemption, and circular wait. The document outlines strategies to handle deadlocks through prevention, avoidance, and detection and recovery. It describes resource allocation graphs to model deadlocks and the conditions for deadlocks using AND and OR resource allocation. Finally, it discusses different techniques for deadlock prevention, detection, and recovery in a system.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
Deadlock and memory management -- Operating SystemEktaVaswani2
This document discusses operating system resources, deadlocks, and memory management. It defines system resources as any usable parts of a computer that can be controlled and assigned by the operating system. It describes the four conditions required for a deadlock and methods for detecting, avoiding, and recovering from deadlocks such as terminating processes. It also discusses memory management techniques like paging, swapping, and virtual memory that allow more programs to reside in memory than the physical memory size.
This document describes a course on operating systems with a focus on deadlocks and memory management. It discusses deadlocks in depth, including the necessary conditions for deadlocks, methods for handling them through prevention, avoidance, detection and recovery. For deadlock prevention, it describes how to ensure the hold-and-wait, no preemption and circular wait conditions do not occur. Deadlock avoidance requires knowledge of future resource requests to determine if a process must wait. The document also provides an overview of memory management strategies like swapping, contiguous allocation and paging.
The document discusses deadlock in computer systems. It defines deadlock and lists necessary conditions for deadlock including mutual exclusion, hold and wait, no preemption, and circular wait. It also discusses strategies for dealing with deadlock such as detection, recovery, and prevention/avoidance. The resource allocation graph (RAG) model is introduced as a way to represent system states and detect deadlock. Algorithms like Banker's algorithm aim to avoid deadlock by ensuring safe allocation of resources.
Deadlocks occur when a set of blocked processes each hold resources and wait for resources held by other processes in the set, resulting in a circular wait. The four necessary conditions for deadlock are: mutual exclusion, hold and wait, no preemption, and circular wait. The banker's algorithm is a deadlock avoidance technique that requires processes to declare maximum resource needs upfront. It ensures the system is always in a safe state by delaying resource requests that could lead to an unsafe state where deadlock is possible.
This document discusses deadlocks in operating systems. It defines deadlock as when a set of blocked processes each hold a resource and wait for a resource held by another process. It then covers methods for handling deadlocks such as prevention, avoidance, detection, and recovery. Prevention ensures deadlock conditions cannot occur. Avoidance allows the system to deny requests that could lead to deadlock. Detection identifies when a deadlock has occurred. Recovery breaks deadlocks by terminating or preempting processes.
This document discusses deadlocks and techniques for handling them. It begins by defining the four necessary conditions for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It then describes three approaches to handling deadlocks: prevention, avoidance, and detection and recovery. Prevention aims to ensure one of the four conditions never holds. Avoidance uses more information to determine if a request could lead to a deadlock. Detection and recovery allows deadlocks but detects and recovers from them after the fact. The document provides examples of different prevention techniques like limiting resource types that can be held, ordering resource types, and preemption. It also explains the banker's algorithm for deadlock avoidance.
This document discusses deadlock avoidance techniques. It explains the concepts of safe and unsafe states when allocating resources to processes. The resource allocation graph algorithm uses claim and assignment edges to model potential resource requests. Banker's algorithm requires processes to declare maximum resource needs upfront. It uses an allocation matrix and need matrix to determine if allocating resources to a process will result in an unsafe state. An example demonstrates tracking available resources and determining if processes can safely obtain requested resources without causing deadlock.
This document discusses deadlock in computer systems. It defines deadlock as when a set of processes are blocked waiting for resources held by other processes in the set. Four necessary conditions for deadlock to occur are outlined: mutual exclusion, hold and wait, no preemption, and circular wait. Strategies to handle deadlock such as prevention, detection, avoidance, and an integrated approach combining multiple strategies are also discussed. Examples of different resource types that can be involved in deadlock are provided.
This document discusses various approaches to handling deadlocks in operating systems, including deadlock prevention, avoidance, detection, and recovery. It describes the four necessary conditions for deadlock, and models the problem using resource allocation graphs. Prevention methods aim to enforce constraints to ensure deadlock cannot occur, while avoidance algorithms dynamically monitor the system state to guarantee safety. Detection algorithms periodically search allocation graphs or wait-for graphs to find cycles indicating deadlock. Recovery requires rolling back processes to free locked resources.
The document summarizes different approaches to handling deadlocks in operating systems, including prevention, avoidance, detection, and recovery. It describes the four conditions required for deadlock, and models for representing resource allocation and processes waiting for resources, such as resource allocation graphs and wait-for graphs. Detection algorithms allow the system to enter a deadlocked state and then identify cycles in wait-for graphs to detect deadlocks.
This document summarizes key concepts related to deadlock avoidance in operating systems. It discusses the four conditions for deadlock, describes the concept of a safe state for resource allocation, and provides an example of modeling resource allocation using a resource allocation graph. The document is presented as part of a course on operating systems, covering topics such as deadlock avoidance, safe state determination, and modeling resource allocation through graphs.
There are three main approaches to handling deadlocks: prevention, avoidance, and detection with recovery. Prevention methods constrain how processes request resources to ensure at least one necessary condition for deadlock cannot occur. Avoidance requires advance knowledge of processes' resource needs to decide if requests can be immediately satisfied. Detection identifies when a deadlocked state occurs and recovers by undoing the allocation that caused it.
Deadlocks can be addressed through four main strategies: detection and recovery, avoidance, and prevention. Prevention ensures that at least one of the four conditions for deadlock never occurs, such as by assigning a numeric order to resources and requiring processes request them in that order to avoid circular waits.
This document summarizes a chapter on deadlocks from an operating systems textbook. It defines deadlock as when a set of blocked processes wait for resources held by each other. Four conditions must be met for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include prevention, avoidance, detection, and recovery. Prevention ensures deadlocks cannot occur by restricting resource usage. Avoidance dynamically checks the system state remains safe to prevent deadlocks. Detection allows deadlocks but recovers the system. Recovery options are terminating processes or preempting resources.
The implementation of Banker's algorithm, data structure and its parserMatthew Chang
The document summarizes a student project presentation on implementing Banker's algorithm for deadlock avoidance. It includes:
1) An overview of Banker's algorithm and how it checks for safe states to avoid deadlock by dynamically evaluating resource requests.
2) Details on the data structures and parsing approach used to represent the banker's algorithm information and process resource requests.
3) A demonstration of the program loading sample data from a file, displaying the banker's algorithm information, and handling different user commands and error scenarios.
The document discusses deadlocks in operating systems. It defines deadlock as a situation where a set of processes are blocked waiting for resources held by other processes in the set, resulting in none of the processes making any progress. Four conditions must be met for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. The document presents examples to illustrate deadlock and discusses different strategies for dealing with it, including deadlock prevention, avoidance, and detection and recovery. It specifically describes the Banker's Algorithm for deadlock avoidance.
This document discusses deadlocks, including the four conditions required for a deadlock, methods to avoid deadlocks like using safe states and Banker's Algorithm, ways to detect deadlocks using wait-for graphs and detection algorithms, and approaches to recover from deadlocks such as terminating processes or preempting resources.
This document discusses deadlocks in operating systems. It defines a deadlock as a set of blocked processes that are each holding a resource and waiting for a resource held by another process. Four conditions must be met for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlocks can be modeled using directed resource allocation graphs. Methods for handling deadlocks include prevention, avoidance, detection, and recovery.
This document provides details on a student project to design a human-carrying ornithopter (mechanical flying machine) that is controlled via radio frequency and has surveillance capabilities. The ornithopter's wings are designed based on bats, beetles, and dragonflies. It uses various small mechanical and electrical components like gears, springs, motors, a wireless camera, microcontroller, and battery. The microcontroller helps process input from sensors to control the ornithopter. The document provides specifications of the components and concludes that ornithopter design remains an obscure area of research compared to fixed-wing aircraft.
The document outlines a turnaround algorithm created by Blackstone Synergy Consulting Group to help struggling small and medium enterprises (SMEs) in Kenya. The algorithm involves liquidating debt to allow for organic growth, improving operating fundamentals through skills training and quality enhancements, and restructuring finances. Blackstone would appoint a receiver manager and implement interventions over 12 quarters to transform business processes, with quarterly reviews to track progress on benchmarks. The goal is for SMEs to achieve organic growth, increased equity earnings, and knowledge capital formation to ensure future success.
This document describes an ornithopter project created by a group of students. It provides background on ornithopters, including that they are aircraft that fly by flapping wings like birds. It discusses the aerodynamics of flapping flight and how designers seek to mimic birds and insects. The document also outlines the history of ornithopters, current projects worldwide, and details of the students' model including its components, mechanism, and potential applications such as surveillance.
This document describes a mini project on a flying wing mechanism conducted by students at Vishwakarma Institute of Technology in Pune, India. It provides an introduction to ornithopters, which are aircraft that fly by flapping wings in imitation of birds. The project involved designing a mechanism to power flapping wings based on research into wing design principles and prior ornithopter projects from around the world. The goal was to apply knowledge gained from studying flapping flight aerodynamics and biomimicry of bird wing motions.
This document discusses several topics related to operating systems and computer science. It begins by discussing storage media such as CDs, DVDs, tapes, and solid state storage. It then poses questions about why operating systems should be studied and some benefits of doing so. Specifically, it notes that operating systems are large, complex software that manages hardware resources and concurrency. The document also discusses why operating systems will not go away due to their fundamental role in making hardware useful. It provides an overview of the capstone operating systems course and focuses on design and implementation challenges. Finally, it covers some administrative details of the course.
1) A Petri net is a graphical modeling tool used to represent systems with concurrent, asynchronous components. It consists of places, transitions, and arcs between them.
2) The document discusses using Petri nets to model resource sharing between two processors to avoid deadlocks. It defines deadlocks and describes the banker's algorithm for deadlock avoidance.
3) The banker's algorithm works by ensuring the system is always in a safe state where all processes can complete even if maximum resources are requested. It maintains data structures to track available, allocated, and needed resources.
This document discusses concurrency and deadlocks in operating systems. It describes how processes compete for limited resources which can result in deadlocks where a set of processes are permanently blocked waiting for each other's resources. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Systems address deadlocks through prevention, avoidance, and detection techniques. Prevention excludes deadlock by design, avoidance dynamically allocates resources to avoid unsafe states, and detection identifies deadlocks to recover processes.
2009 Punjab Technical University B.C.A OPERATING SYSTEM Question paperMonica Sabharwal
The document contains an exam for an Operating Systems course, including:
1) A 10 question short answer section covering topics like the main functions of an OS, multiprogramming, threads, deadlocks, dynamic linking, paging, interrupts vs traps, system programs, and dispatchers.
2) A longer answer section with 4 questions, including questions on batch processing systems, scheduling queues/algorithms, analyzing turnaround and waiting times for different scheduling algorithms, the dining philosophers problem and deadlocks, page sizes and addresses, thrashing prevention, file operations, OS security threats, and data encryption.
The exam tests students' understanding of fundamental OS concepts through definitions, explanations of concepts, analyzing examples, and
Deadlock is a very important topic in operating system. In this presentation slide, try to relate deadlock with real life scenario and find out some solution with two main algorithm- Safety and Banker's Algorithm.
The document discusses deadlocks in operating systems. It defines the four conditions for deadlock - mutual exclusion, hold and wait, no preemption, and circular wait. It explains resource allocation graphs and how they can be used to detect deadlocks. The document also covers deadlock prevention methods like mutual exclusion, holding and waiting, preemption, and imposing a total ordering of resources. It describes Banker's algorithm for deadlock prevention and detection with multiple instances of resources. Finally, it discusses different approaches for deadlock recovery like process termination and resource preemption.
Deadlock occurs when a set of blocked processes form a circular chain where each process waits for a resource held by the next process. There are four necessary conditions for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. The banker's algorithm avoids deadlock by tracking available resources and process resource needs, and only allocating resources to a process if it will not cause the system to enter an unsafe state where deadlock could occur. It uses matrices to represent allocation states and evaluates requests to ensure allocating resources does not lead to deadlock.
This document discusses deadlocks in database systems. It explains that deadlocks occur when two or more competing actions get stuck waiting on each other to finish. It then provides an example of a deadlock between two dogs, Tony and Jake, fighting over bones. It demonstrates how to detect and debug deadlocks using MySQL status commands and log files. Finally, it offers best practices like defining proper indexes to avoid deadlocks and handling them through retry logic or manual locking.
This document discusses the history and applications of 3D holographic technology. It begins by explaining that 3D technology has existed since the 1830s with the invention of stereoscopic photography. Different types of 3D glasses are described that allow the illusion of 3D to be viewed. The document outlines key milestones in the development of holography, from its discovery in 1947 to its use in various applications today such as movies, advertising, gaming, education and more. The future potential of holographic technology is envisioned, including uses in education, medicine and everyday devices.
This document discusses different strategies for handling deadlocks in operating systems, including prevention, avoidance, detection, and recovery. Prevention methods aim to ensure that one of the four necessary conditions for deadlock does not occur. Avoidance allows all conditions but detects unsafe states and stops requests that could lead to deadlock. Detection identifies when a deadlock has occurred. Recovery methods regain resources by terminating processes or preempting resources to break cycles in resource allocation graphs.
This document contains a question bank on various topics in operating systems including:
1. Process synchronization questions focusing on critical section problems, semaphores, and solutions for two processes.
2. Memory management questions on paging and segmentation.
3. Deadlock questions on safe/unsafe states, bankers algorithm, prevention/avoidance strategies, and recovery from deadlocks.
4. CPU scheduling questions on algorithms like FCFS, RR, SJF and characteristics like short term, long term and medium term schedulers.
5. Process management questions on states, control blocks, creation/termination, and interprocess communication.
The questions provided are meant to help students study notes
The document discusses deadlocks that can occur in a multiprocessing system where multiple processes compete for limited resources. A deadlock occurs when a process is waiting for a resource held by another waiting process, resulting in a circular wait. The document outlines the four conditions required for deadlock and describes methods to prevent deadlocks, including imposing a total ordering of resource requests and avoiding holding resources while waiting for additional resources.
The document discusses deadlocks in operating systems. It defines deadlock as a situation where a set of processes are blocked waiting for resources held by each other in a cyclic manner. Four necessary conditions for deadlock are described: mutual exclusion, hold and wait, no preemption, and circular wait. Methods for handling deadlocks include prevention, avoidance, and detection/recovery. Prevention ensures one of the conditions cannot occur through protocols like requiring exclusive resource requests, non-preemptive allocation, or imposing a total ordering of resource types.
In these slides I discussed about deadlock,causes of deadlock,effects of deadlock,conditions of deadlock,resource allocation graph,deadlock handling strategies,deadlock prevention,deadlock avoidance,deadlock avoidance and resolution....I haven't touch algorithms section in these slides.....and last thing I want to say that don't forget to follow me...
This document discusses deadlock prevention and recovery in computer systems. It defines deadlock as when a set of blocked processes each hold a resource and wait for a resource held by another process. The document outlines the system model involving resources and processes. It describes deadlock characterization including conditions like mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include prevention techniques like avoiding one of the four conditions, detection of deadlocks in a resource allocation graph, and recovery methods like process termination or resource preemption.
This document discusses deadlock prevention and recovery in computer systems. It begins by defining deadlock and describing the conditions required for deadlock to occur. It then presents a system model and characterizes deadlocks using resource allocation graphs. The document outlines four main methods for handling deadlocks: prevention, avoidance, detection, and recovery. It focuses on prevention, describing four different approaches to ensure at least one deadlock condition does not hold: eliminating mutual exclusion, hold and wait, no preemption, or circular wait. The document also briefly discusses deadlock detection and two recovery methods: process termination and resource preemption.
This document discusses deadlocks in computer systems. It defines a deadlock as when a set of blocked processes each hold a resource and wait to acquire a resource held by another process, creating a circular wait. The document outlines methods to prevent, avoid, detect, and recover from deadlocks. These include deadlock prevention through proper resource allocation and deadlock recovery by undoing processes or preempting resources to break cycles in the resource allocation graph.
Lecture # 10-11 for deadlock operating system.pptRiaanSadiq
A deadlock is a state in a computer system where two or more processes are unable to proceed because each is waiting for the other to release a resource. This impasse leads to a standstill in the execution of programs, resulting in a halt of system operations. Deadlocks typically occur in multitasking or multi-process environments, where processes compete for shared resources such as memory, files, or hardware devices.
The deadlock scenario involves a cyclic waiting condition, where each process holds a resource and waits for another resource held by a different process. This circular dependency prevents any of the involved processes from making progress, causing the entire system to become unresponsive.
Key conditions for a deadlock to occur include mutual exclusion, where resources cannot be simultaneously shared; hold and wait, where a process holds resources while waiting for additional ones; no preemption, where resources cannot be forcibly taken away from a process; and circular wait, where a cycle of processes forms, each waiting for the next to release a resource.
Deadlock prevention and resolution strategies are crucial in system design to ensure efficient resource utilization and prevent the potential negative impacts of deadlocks on overall system performance.A deadlock is a state in a computer system where two or more processes are unable to proceed because each is waiting for the other to release a resource. This impasse leads to a standstill in the execution of programs, resulting in a halt of system operations. Deadlocks typically occur in multitasking or multi-process environments, where processes compete for shared resources such as memory, files, or hardware devices.
The deadlock scenario involves a cyclic waiting condition, where each process holds a resource and waits for another resource held by a different process. This circular dependency prevents any of the involved processes from making progress, causing the entire system to become unresponsive.
Key conditions for a deadlock to occur include mutual exclusion, where resources cannot be simultaneously shared; hold and wait, where a process holds resources while waiting for additional ones; no preemption, where resources cannot be forcibly taken away from a process; and circular wait, where a cycle of processes forms, each waiting for the next to release a resource.
Deadlock prevention and resolution strategies are crucial in system design to ensure efficient resource utilization and prevent the potential negative impacts of deadlocks on overall system performance.A deadlock is a state in a computer system where two or more processes are unable to proceed because each is waiting for the other to release a resource. This impasse leads to a standstill in the execution of programs, resulting in a halt of system operations.
This document discusses deadlocks in operating systems. It defines deadlock as when a set of processes are all waiting for resources held by each other in a cyclic manner, preventing any progress. Four conditions must hold for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Detection methods include using a resource allocation graph to model processes and resources. Prevention techniques enforce restrictions like requiring processes request resources in a predefined order to avoid circular waits. The banker's algorithm is also described, which uses matrices to model available resources and ensure the system remains in a safe state to avoid deadlocks.
Deadlocks operating system To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks
To present a number of different methods for preventing, avoiding, or detecting deadlocks in a computer system
e.t.c
This document discusses deadlocks in a multiprogramming system. It defines deadlock as a situation where a set of processes are waiting indefinitely for resources held by each other in a circular chain. Four necessary conditions for deadlock are explained: mutual exclusion, hold and wait, no preemption, and circular wait. Methods for handling deadlocks include prevention, avoidance, detection and recovery. Prevention methods aim to enforce restrictions to ensure at least one condition cannot be met, such as allocating all resources for a process upfront or not allowing processes to hold resources while waiting for others.
This document discusses different approaches to handling deadlocks in operating systems. It begins by defining deadlocks and providing examples. It then describes four conditions required for deadlock to occur. Various methods for handling deadlocks are discussed, including prevention, avoidance, detection, and recovery. Prevention methods aim to restrict system states that could lead to deadlocks. Avoidance methods dynamically allocate resources to ensure the system cannot reach an unsafe state. Detection methods identify deadlocks after they occur, while recovery rolls back processes or terminates them. A combined approach uses elements of multiple methods.
The objectives of Deadlocks in Operating Systems are:
- To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks
- To present a number of different methods for preventing or avoiding deadlocks in a computer system
The document summarizes deadlock concepts including:
1) Deadlock occurs when a set of processes are blocked waiting for resources held by each other in a cyclic manner, preventing any progress.
2) Four conditions must hold simultaneously for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait.
3) Methods to handle deadlocks include prevention, avoidance, detection, and recovery. Prevention ensures deadlocks cannot occur by violating one of the four conditions. Avoidance dynamically ensures the system is always in a safe state where deadlocks cannot occur.
The document discusses the deadlock problem in operating systems. It defines deadlock as a state where a set of blocked processes are each holding resources and waiting for additional resources held by other processes in the set, resulting in none of the processes being able to progress. Four conditions must hold simultaneously for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Methods for handling deadlocks include prevention, avoidance, and detection/recovery. The banker's algorithm is presented as a deadlock avoidance strategy that uses a resource allocation graph and ensures the system is always in a safe state where deadlocks cannot occur.
The document discusses deadlocks in computer systems. It defines deadlocks as a situation where two or more competing processes are waiting for resources held by each other, leading to indefinite blocking. The key characteristics of deadlocks are mutual exclusion of resources, hold and wait conditions, no preemption of allocated resources, and circular wait dependencies between processes. The document outlines several methods to handle deadlocks, including prevention, avoidance through algorithms like the banker's algorithm, and detection and recovery.
The document discusses deadlocks in operating systems. It defines a deadlock as a situation where multiple processes are waiting indefinitely for resources held by each other in a cyclic manner. Four necessary conditions for a deadlock to occur are mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include deadlock prevention by ensuring at least one condition is never satisfied, deadlock avoidance by tracking resource usage to prevent unsafe states, and deadlock detection and recovery by allowing deadlocks to occur and resolving them. The banker's algorithm is presented for deadlock avoidance with multiple resource instances using data structures to track available, allocated, and needed resources.
This document discusses deadlocks in computer systems. It begins by describing a system model where processes request, use, and release finite resources. It then defines what constitutes a deadlock and provides examples. The necessary conditions for deadlock are explained as mutual exclusion, hold and wait, no preemption, and circular wait. Methods to handle deadlocks include prevention, avoidance, detection and recovery. Prevention techniques aim to satisfy one of the necessary conditions, such as imposing a total ordering of resource requests. Avoidance uses additional information to decide if a request could lead to a deadlock.
The document summarizes key topics about deadlocks in operating systems including deadlock characterization, prevention, and avoidance. It defines deadlock as a set of blocked processes where each process is waiting for a resource held by another in the set. Four conditions must be met for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlock prevention methods ensure systems never enter a deadlock state while avoidance uses a safe state algorithm and resource ordering to dynamically prevent unsafe states.
The document discusses techniques for preventing deadlocks in operating systems. It covers four main techniques - hold and wait protocol, no preemption protocol, requesting resources in increasing order of enumeration to prevent circular wait conditions, and ensuring at least one of the four necessary conditions for deadlock is not met. The protocols aim to enforce that processes request all resources before starting or release resources before requesting new ones to avoid deadlock situations.
A deadlock occurs in a concurrent system when two or more processes are unable to proceed because each is waiting for another to release a resource. This situation leads to a standstill where none of the processes can complete their execution.
Optimizing Gradle Builds - Gradle DPE Tour Berlin 2024Sinan KOZAK
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Embedded machine learning-based road conditions and driving behavior monitoringIJECEIAES
Car accident rates have increased in recent years, resulting in losses in human lives, properties, and other financial costs. An embedded machine learning-based system is developed to address this critical issue. The system can monitor road conditions, detect driving patterns, and identify aggressive driving behaviors. The system is based on neural networks trained on a comprehensive dataset of driving events, driving styles, and road conditions. The system effectively detects potential risks and helps mitigate the frequency and impact of accidents. The primary goal is to ensure the safety of drivers and vehicles. Collecting data involved gathering information on three key road events: normal street and normal drive, speed bumps, circular yellow speed bumps, and three aggressive driving actions: sudden start, sudden stop, and sudden entry. The gathered data is processed and analyzed using a machine learning system designed for limited power and memory devices. The developed system resulted in 91.9% accuracy, 93.6% precision, and 92% recall. The achieved inference time on an Arduino Nano 33 BLE Sense with a 32-bit CPU running at 64 MHz is 34 ms and requires 2.6 kB peak RAM and 139.9 kB program flash memory, making it suitable for resource-constrained embedded systems.
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This document serves as a comprehensive step-by-step guide on how to effectively use PyCharm for remote debugging of the Windows Subsystem for Linux (WSL) on a local Windows machine. It meticulously outlines several critical steps in the process, starting with the crucial task of enabling permissions, followed by the installation and configuration of WSL.
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4. Deadlock
• Multiprogramming ? – many processes –few
resources.
• States of processes –Ready-Run-Wait.
• Def:A set of blocked processes each holding a
resource and waiting to acquire a resource held
by another process in the set.
• Ex. When two trains approach each other.
• We describe methods that an operating system
can use to prevent or deal with deadlocks
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5. The Deadlock Problem
• Example
– System has 2 disk drives.
– P1 and P2 each hold one disk drive and each needs
another one.
• Example
– semaphores A and B, initialized to 1
P0 P1
wait (A); wait(B)
wait (B); wait(A)
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6. Bridge Crossing Example
• Traffic only in one direction.
• Each section of a bridge can be viewed as a resource.
• If a deadlock occurs, it can be resolved if one car backs
up (preempt resources and rollback).
• Several cars may have to be backed up if a deadlock
occurs.
• Starvation is possible.
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10. 11/22/2015 SDM SVV OS 10
Deadlock in relationships is a part of boredom, stress and unmet expectations. For
example, Deadlock can occur in a situation when a girl1 is wanting for a guy2, who is
acquired by another girl2, and girl2 is wanting for a guy1 that is acquired by girl1. Since,
both girls are waiting for each other to release the guy, the condition is called deadlock.
12. System Model
• Resource types R1, R2, . . ., Rm
CPU cycles, memory space, I/O devices
• Each resource type Ri has Wi instances.
• Each process utilizes a resource as follows:
– request
– use
– release
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13. Deadlock Characterization
1. Mutual exclusion: only one process at a time
can use a resource.
2. Hold and wait: a process holding at least one
resource is waiting to acquire additional
resources held by other processes.
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Deadlock can arise if four conditions hold simultaneously.
14. Deadlock Characterization
3. No preemption: a resource can be released
only voluntarily by the process holding it, after
that process has completed its task.
4. Circular wait: there exists a set {P0, P1, …,
Pn} of waiting processes such that P0 is
waiting for a resource that is held by P1, P1 is
waiting for a resource that is held by P2, …,
Pn–1 is waiting for a resource that is held by
Pn, and Pn is waiting for a resource that is held
by P0.
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Deadlock can arise if four conditions hold simultaneously.
16. Resource allocation graph
• Why u plot Freq Response?
• Cricket results why graphs/plots???
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17. Resource-Allocation Graph
• V is partitioned into two types:
– P = {P1, P2, …, Pn}, the set consisting of all the
processes in the system.
– R = {R1, R2, …, Rm}, the set consisting of all
resource types in the system.
• Request edge – directed edge P1 Rj
• Assignment edge – directed edge Rj Pi
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A set of vertices V and a set of edges E.
18. Resource-Allocation Graph (Cont.)
• Process
• Resource Type with 4 instances
• Pi requests instance of Rj
• Pi is holding an instance of Rj
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Pi
Pi
19. Example of a Resource Allocation Graph
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P={P1,P2,P3}
R={R1,R2,R3,R4}
E={P1R1, P2R3,R1P1,R3P3,R2P1,R2P2}
20. Example of a Resource Allocation Graph
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Instances R1=1, R2=2, R3=1, R4=3
Process states: P1 holding R2 and is waiting for an
instance of resource type R1, similarly P2, P3
22. Graph With A Cycle But No Deadlock
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Is there any Deadlock?
23. Basic Facts
• If graph contains no cycles no deadlock.
• If graph contains a cycle
– if only one instance per resource type, then
deadlock.
– if several instances per resource type, possibility of
deadlock.
•
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24. Summary
• Examples-deadlock
• Four conditions for deadlock
– M H N C
• Resource allocation graph?
• Cycle
– No cycle – 100% no deadlock
– Cycle
• Single instances – 100% Deadlock
• Many instances – Possibility of deadlock
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25. Methods for Handling Deadlocks
• Ensure that the system will never enter a
deadlock state.
• Allow the system to enter a deadlock state and
then recover.
• Ignore the problem and pretend that deadlocks
never occur in the system; used by most
operating systems, including UNIX.
•
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26. Deadlock Prevention
• Four conditions for Deadlock
– Mutual exclusion
– Hold and wait
– No preemption
– Circular wait
• Prevent Deadlock Ensure that at least one
of these cannot hold (any one is false)
• Prevention is better than cure
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27. Deadlock Prevention
• Mutual Exclusion –This condition must hold for
non-sharable resources. Ex. Printer. Read only
files No need to wait for access. To make this
false all resources should be sharable.
• Hold and Wait –Protocols, (No wait/ No Hold)
• Process must request all resources and be
allocated. (No wait)
• Must guarantee that whenever a process requests
a resource, it does not hold any other resources.
(No Hold)
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28. Deadlock Prevention
• Ex. Copy data from Tape drive to disc, sorts
the disk file and then prints result to a printer.
• No wait: Request Tape drive, Disk file and
printer.
• No Hold: Request Tape drive and disk file,
Release resources, again request disk file and
printer.
• Dis: Protocol 1 Resource Utilization is less.
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29. Deadlock Prevention
• No Preemption –
– If a process that is holding some resources requests
another resource that cannot be immediately
allocated to it, then all resources currently being
held are released.
– Preempted resources are added to the list of
resources for which the process is waiting.
– Process will be restarted only when it can regain
its old resources, as well as the new ones that it is
requesting.
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30. Deadlock Prevention
• Circular Wait – impose a total ordering of all
resource types, and require that each process
requests resources in an increasing order of
enumeration.
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31. – Ex Tape drive -1; Disk drive-5 and Printer -9 Each
process can request resources in increasing order.
– 1:The process can request instance of resource
type rj iff F(Rj)>F(Ri). (Ri –is holding resources)
– 2:Whenever Pi req for Rj, it has released any
resources Ri such that F(Ri)>=F(Rj).
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F(tapedrive)=1
F(disk drive)=5
F(printer)=9
32. Deadlock Avoidance
• Deadlock prevention side effect– Low device
utilization and reduced system through put.
• Alternative Method—Require additional
information about how resources are to be
requested.
• Ex. P1 req R1 then R2 and P2 req R2 then R1
possible to avoid deadlock.
• Deadlock avoidance algorithm dynamically
examines resource allocation state to ensure
that there is no circular wait.
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33. Deadlock Avoidance
• Safe State: A system is in safe state if there
exists a safe sequence.
• When a process requests an available resource,
system must decide if immediate allocation leaves
the system in a safe state. (Budget Plan/Bank)
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34. • Safe sequence
– If Pi resource needs are not immediately available,
then Pi can wait until all Pj have finished.
– When Pj is finished, Pi can obtain needed
resources, execute, return allocated resources, and
terminate.
– When Pi terminates, Pi +1 can obtain its needed
resources, and so on.
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35. Basic Facts
• If a system is in safe state no deadlocks.
• If a system is in unsafe state possibility of
deadlock.
• Avoidance ensure that a system will never
enter an unsafe state.
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37. Safe sequence
• Ex.
• Is there any safe sequence?
• 3p15 P0 10 P2 12
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Process Max.
Needs
Holding Current
Needs
Total Available
P0 10 5 5 12 3
P1 4 2 2
P2 9 2 2
38. Safe sequence
• Ex.
• Is there any safe sequence?
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Process Max.
Needs
Holding Current
Needs
Total Available
P0 10 5 5 12 2
P1 4 2 2
P2 9 3 2
39. Avoidance algorithms
• Single instance of a resource type. Use a
resource-allocation graph
• Multiple instances of a resource type. Use the
banker’s algorithm (Not bakery Algorithm)
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40. Resource-Allocation Graph Scheme
• Claim edge Pi Rj indicated that process Pi may
request resource Rj; represented by a dashed line.
• Claim edge converts to request edge when a
process requests a resource.
• Request edge converted to an assignment edge
when the resource is allocated to the process.
• Resources must be claimed a priori in the system.
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42. Unsafe State In Resource-Allocation Graph
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43. Resource-Allocation Graph Algorithm
• Suppose that process Pi requests a resource Rj
• The request can be granted only if converting
the request edge to an assignment edge does
not result in the formation of a cycle in the
resource allocation graph
•
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44. Banker’s Algorithm
• Multiple instances.
• Each process must a priori claim maximum
use.
• When a process requests a resource it may
have to wait.
• When a process gets all its resources it must
return them in a finite amount of time.
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45. Data Structures for the Banker’s Algorithm
• Available: Vector of length m. If available [j] = k,
there are k instances of resource type Rj available.
• Max: n x m matrix. If Max [i,j] = k, then process
Pi may request at most k instances of resource
type Rj.
• Allocation: n x m matrix. If Allocation[i,j] = k
then Pi is currently allocated k instances of Rj.
• Need: n x m matrix. If Need[i,j] = k, then Pi may
need k more instances of Rj to complete its task.
Need [i,j] = Max[i,j] – Allocation [i,j].
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Data Structures for the Banker’s Algorithm
46. • Ex.
Allocation Max Available
A B C A B C A B C
P0 0 1 0 7 5 3 3 3 2
P1 2 0 0 3 2 2
P2 . … …..
…
Need
A B C
P0 7 4 3
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47. Safety Algorithm
1.Let Work and Finish be vectors of length m and
n, respectively. Initialize:
Work = Available
Finish [i] = false for i = 0, 1, …, n- 1.
2.Find an i such that both:
(a) Finish [i] = false
(b) Needi Work
If no such i exists, go to step 4.
3.Work = Work + Allocationi
Finish[i] = true
go to step 2.
4.If Finish [i] == true for all i, then the system is in
a safe state.
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48. Resource-Request Algorithm for Process Pi
Requesti = request vector for process Pi. If
Requesti [j] = k then process Pi wants k
instances of resource type Rj.
When a request for resources is made by process
Pi, the following actions are taken:
1.If Requesti Needi go to step 2. Otherwise, raise
error condition, since process has exceeded its
maximum claim.
2.If Requesti Available, go to step 3. Otherwise Pi
must wait, since resources are not available.
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49. 3. Pretend to allocate requested resources to
Pi by modifying the state as follows:
Available = Available – Request;
Allocationi = Allocationi + Requesti;
Needi = Needi – Requesti;
If safe the resources are allocated to Pi.
If unsafe Pi must wait, and the old resource-
allocation state is restored
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Find the safe sequence
50. Example of Banker’s Algorithm
• 5 processes P0 through P4;
3 resource types:
A (10 instances), B (5instances), and C (7 instances).
• Snapshot at time T0:
Allocation Max Available? Need?
A B C A B C A B C
P0 0 1 0 7 5 3
P1 2 0 0 3 2 2
P2 3 0 2 9 0 2
P3 2 1 1 2 2 2
P4 0 0 2 4 3 3
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3 3 2
Total 7 2 5
51. Example of Banker’s Algorithm
Allocation Max Available Need=max-Allocation?
A B C A B C A B C
P0 0 1 0 7 5 3
P1 2 0 0 3 2 2
P2 3 0 2 9 0 2
P3 2 1 1 2 2 2
P4 0 0 2 4 3 3
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3 3 2
Total 7 2 5
52. • The content of the matrix Need is defined to be Max –
Allocation.
Need
A B C
P0 7 4 3
P1 1 2 2
P2 6 0 0
P3 0 1 1
P4 4 3 1
• Is the system in a safe state?
• since the sequence < P1, P3, P4, P2, P0> satisfies safety
criteria.
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Available is 3 3 2
53. Example: P1 Request (1,0,2)
• Check that Request Available (that is, (1,0,2) (3,3,2)
true.
Allocation Need Available
A B C A B C A B C
P0 0 1 0 7 4 3 2 3 0
P1 3 0 2 0 2 0
P2 3 0 1 6 0 0
P3 2 1 1 0 1 1
P4 0 0 2 4 3 1
• Executing safety algorithm shows that sequence < P1, P3,
P4, P0, P2> satisfies safety requirement.
• Can request for (3,3,0) by P4 be granted?
• Can request for (0,2,0) by P0 be granted?
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Is the system safe?
54. Deadlock Detection
• If a system does not employ either a deadlock-
prevention or a deadlock avoidance algorithm
– Then a deadlock situation may occur.
• In this environment, the system must provide:
– Detection algorithm
– Recovery scheme
• Two methods
– Single Instance of Each Resource Type
– Several Instances of a Resource Type
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55. Single Instance of Each Resource Type
• Maintain wait-for graph
– Nodes are processes.
– Pi Pj if Pi is waiting for Pj.
• Periodically invoke an algorithm that searches
for a cycle in the graph. If there is a cycle,
there exists a deadlock.
• An algorithm to detect a cycle in a graph
requires an order of n2 operations, where n is
the number of vertices in the graph.
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56. Resource-Allocation Graph and Wait-for Graph
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Resource-Allocation Graph Corresponding wait-for graph
57. Several Instances of a Resource Type
• Can we use wait for graph – Cycles-to detect
deadlock?
• The algorithm employs several time-varying
data structures that are similar to those used in
the banker's algorithm
• Can you recall those data structures now…
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58. Several Instances of a Resource Type
• Available: A vector of length m indicates the
number of available resources of each type.
• Allocation: An n x m matrix defines the number
of resources of each type currently allocated to
each process.
Request: An n x m matrix indicates the current
request of each process. If Request [ij] = k, then
process Pi is requesting k more instances of
resource type. Rj.
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59. Detection Algorithm
1.Let Work and Finish be vectors of length m
and n, respectively Initialize:
(a) Work = Available
(b)For i = 1,2, …, n, if Allocationi 0, then
Finish[i] = false; otherwise, Finish[i] = true.
2.Find an index i such that both:
(a) Finish[i] == false
(b)Requesti Work
If no such i exists, go to step 4.
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60. 3.Work = Work + Allocationi
Finish[i] = true
go to step 2.
4.If Finish[i] == false, for some i, 1 i n, then
the system is in deadlock state. Moreover, if
Finish[i] == false, then Pi is deadlocked.
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Algorithm requires an order of (m x n2)operations to detect
whether the system is in deadlocked state.
61. Example of Detection Algorithm
• Five processes P0 through P4; three resource types
A (7 instances), B (2 instances), and C (6 instances).
• Snapshot at time T0:
Allocation Request Available
A B C A B C A B C
P0 0 1 0 0 0 0 0 0 0
P1 2 0 0 2 0 2
P2 3 0 3 0 0 0
P3 2 1 1 1 0 0
P4 0 0 2 0 0 2
• Is the system in safe state?
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62. Example of Detection Algorithm
• Five processes P0 through P4; three resource types
A (7 instances), B (2 instances), and C (6 instances).
• Snapshot at time T0:
AllocationRequest Available
A B C A B C A B C
P0 0 1 0 0 0 0 0 0 0
P1 2 0 0 2 0 2
P2 3 0 3 0 0 0
P3 2 1 1 1 0 0
P4 0 0 2 0 0 2
• Sequence <P0, P2, P3, P1, P4> will result in Finish[i] =
true for all i.
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63. Example of Detection Algorithm
Allocation Request Available (7 2 6)
A B C A B C A B C
P0 0 1 0 0 0 0 0 0 0
P1 2 0 0 2 0 2
P2 3 0 3 0 0 0
P3 2 1 1 1 0 0
P4 0 0 2 0 0 2
• Sequence <P0,P2,P3-P1, P4> will result in
Finish[i] = true for all i.
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Process completion
P0- 0 1 0
P2-3 1 3
P3-5 2 4
P1-7 2 4
P4-7 2 6
64. • P2 requests an additional instance of type C.
Request
A B C available 0 0 0
P0 0 0 0
P1 2 0 1
P2 0 0 1
P3 1 0 0
P4 0 0 2
• Is the system in safe state?
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65. • P2 requests an additional instance of type C.
Request
A B C
P0 0 0 0
P1 2 0 1
P2 0 0 1
P3 1 0 0
P4 0 0 2
• State of system?
– Can reclaim resources held by process P0, but insufficient
resources to fulfill other processes; requests.
– Deadlock exists, consisting of processes P1, P2, P3, and P4.
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P0- 0 1 0
66. Detection-Algorithm Usage
• When, and how often, to invoke depends on:
– How often a deadlock is likely to occur?
– How many processes will need to be rolled back?
• one for each disjoint cycle
• If detection algorithm is invoked arbitrarily,
there may be many cycles in the resource
graph and so we would not be able to tell
which of the many deadlocked processes
“caused” the deadlock.
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67. Recovery from Deadlock: Process Termination
• Abort all deadlocked processes.
• Abort one process at a time until the deadlock cycle is
eliminated.
• In which order should we choose to abort?
– Priority of the process.
– How long process has computed, and how much longer to
completion.
– Resources the process has used.
– Resources process needs to complete.
– How many processes will need to be terminated.
– Is process interactive or batch?
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68. Recovery from Deadlock: Resource Preemption
• Selecting a victim – minimize cost.
• Rollback – return to some safe state, restart
process for that state.
• Starvation – same process may always be
picked as victim, include number of rollback in
cost factor.
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