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 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.
Deadlock occurs when two or more processes are waiting for resources held by each other in a circular chain, resulting in none of the processes making progress. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlock can be addressed through prevention, avoidance, detection, or recovery methods. Prevention aims to eliminate one of the four conditions, while avoidance techniques like the safe state model and Banker's Algorithm guarantee a safe allocation order to avoid circular waits.
There are three main methods for dealing with deadlocks in an operating system: prevention, avoidance, and detection with recovery. Prevention ensures that the necessary conditions for deadlock cannot occur through restrictions on resource allocation. Avoidance uses additional information about future resource needs and requests to determine if allocating resources will lead to an unsafe state. Detection identifies when a deadlock has occurred, then recovery techniques like process termination or resource preemption are used to resolve it. No single approach is suitable for all resource types, so systems often combine methods by applying the optimal one to each resource class.
This document summarizes the Banker's Algorithm, which is used to determine if a set of pending processes can safely acquire resources or if they should wait due to limited resources. It outlines the key data structures used like Available, Max, Allocation, and Need matrices to track current resources. The Safety Algorithm is described to check if the system is in a safe state by finding a process that can terminate and release resources. The Resource-Request Algorithm simulates allocating resources to a process and checks if it leads to a safe state before actual allocation.
Deadlock occurs when two or more competing processes are each waiting for resources held by the other, resulting in all processes waiting indefinitely. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Techniques to prevent deadlock include attacking each condition: allowing some resources to be shared, requiring processes request all resources at start, allowing preemption of resources, and imposing a global numbering on resource requests.
Adbms 11 object structure and type constructorVaibhav Khanna
Unique Identity:
An OO database system provides a unique identity to each independent object stored in the database.
This unique identity is typically implemented via a unique, system-generated object identifier, or OID
The main property required of an OID is that it be immutable
Specifically, the OID value of a particular object should not change.
This preserves the identity of the real-world object being represented.
Type Constructors:
In OO databases, the state (current value) of a complex object may be constructed from other objects (or other values) by using certain type constructors.
The three most basic constructors are atom, tuple, and set.
Other commonly used constructors include list, bag, and array.
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.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
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.
Deadlock occurs when two or more processes are waiting for resources held by each other in a circular chain, resulting in none of the processes making progress. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlock can be addressed through prevention, avoidance, detection, or recovery methods. Prevention aims to eliminate one of the four conditions, while avoidance techniques like the safe state model and Banker's Algorithm guarantee a safe allocation order to avoid circular waits.
There are three main methods for dealing with deadlocks in an operating system: prevention, avoidance, and detection with recovery. Prevention ensures that the necessary conditions for deadlock cannot occur through restrictions on resource allocation. Avoidance uses additional information about future resource needs and requests to determine if allocating resources will lead to an unsafe state. Detection identifies when a deadlock has occurred, then recovery techniques like process termination or resource preemption are used to resolve it. No single approach is suitable for all resource types, so systems often combine methods by applying the optimal one to each resource class.
This document summarizes the Banker's Algorithm, which is used to determine if a set of pending processes can safely acquire resources or if they should wait due to limited resources. It outlines the key data structures used like Available, Max, Allocation, and Need matrices to track current resources. The Safety Algorithm is described to check if the system is in a safe state by finding a process that can terminate and release resources. The Resource-Request Algorithm simulates allocating resources to a process and checks if it leads to a safe state before actual allocation.
Deadlock occurs when two or more competing processes are each waiting for resources held by the other, resulting in all processes waiting indefinitely. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Techniques to prevent deadlock include attacking each condition: allowing some resources to be shared, requiring processes request all resources at start, allowing preemption of resources, and imposing a global numbering on resource requests.
Adbms 11 object structure and type constructorVaibhav Khanna
Unique Identity:
An OO database system provides a unique identity to each independent object stored in the database.
This unique identity is typically implemented via a unique, system-generated object identifier, or OID
The main property required of an OID is that it be immutable
Specifically, the OID value of a particular object should not change.
This preserves the identity of the real-world object being represented.
Type Constructors:
In OO databases, the state (current value) of a complex object may be constructed from other objects (or other values) by using certain type constructors.
The three most basic constructors are atom, tuple, and set.
Other commonly used constructors include list, bag, and array.
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.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
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.
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.
Deadlocks-An Unconditional Waiting Situation in Operating System. We must make sure of This concept well before understanding deep in to Operating System. This PPT will understands you to get how the deadlocks Occur and how can we Detect, avoid and Prevent the deadlocks in Operating Systems.
The document discusses race conditions that occur when multiple processes access shared data concurrently. A critical section is a block of code that only one process can execute at a time to avoid race conditions. The critical section problem aims to ensure only one process is in its critical section at once using mutual exclusion. Mutual exclusion methods like semaphores are used to prevent simultaneous access to shared resources like global variables.
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.
Deadlock detection and recovery by saad symbiansaad symbian
1) Deadlock occurs when there is a cycle of processes where each process is waiting for a resource held by the next process in the cycle.
2) Solutions to deadlock include prevention, avoidance, detection and recovery. Prevention ensures deadlock is impossible through restrictions. Avoidance uses scheduling to steer around deadlock. Detection checks for cycles periodically and recovery kills processes or rolls them back to release resources.
3) Deadlock recovery options include killing all deadlocked processes, killing one at a time to release resources, or rolling processes back to a prior safe state instead of killing them. The process to kill or roll back is chosen based on factors like priority, resources used, and amount of work.
The document discusses memory management techniques used in operating systems. It describes logical vs physical addresses and how relocation registers map logical addresses to physical addresses. It covers contiguous and non-contiguous storage allocation, including paging and segmentation. Paging divides memory into fixed-size frames and pages, using a page table and translation lookaside buffer (TLB) for address translation. Segmentation divides memory into variable-sized segments based on a program's logical structure. Virtual memory and demand paging are also covered, along with page replacement algorithms like FIFO, LRU and optimal replacement.
Salman Ahmed presents on deadlocks in computer systems. A deadlock occurs when two programs are preventing each other from accessing shared resources, causing both programs to cease functioning. Deadlocks happen when processes are holding resources and waiting to acquire more resources, but cannot release the initial resources. There are four main approaches to handling deadlocks: prevention, avoidance, detection, and recovery. Prevention eliminates one of the conditions required for a deadlock, while avoidance allows the system to refuse resource requests to avoid entering a deadlocked state.
This presentation describes about the various memory allocation methods like first fit, best fit and worst fit in memory management and also about fragmentation problem and solution for the problem.
This presentation discusses system calls and provides an overview of their key aspects:
System calls provide an interface between processes and the operating system. They allow programs to request services from the OS like reading/writing files. There are different methods of passing parameters to the OS, such as via registers, parameter blocks, or pushing to the stack. System calls fall into categories including process control, file management, device management, information maintenance, and communication. An example is given of how system calls would be used in a program to copy data between two files.
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.
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
1. There are three methods to handle deadlocks: prevention, avoidance, and detection with recovery.
2. Deadlock prevention ensures that at least one of the necessary conditions for deadlock cannot occur. Deadlock avoidance requires processes to declare maximum resource needs upfront.
3. The Banker's algorithm is a deadlock avoidance technique that dynamically checks the resource allocation state to ensure it remains safe and no circular wait can occur.
Two Phase Commit is a protocol that ensures transactions are either fully committed or aborted across multiple database sites. It uses a coordinator node that initiates a prepare phase where other nodes log transaction details and agree/disagree to commit. If all agree, the coordinator initiates a commit phase where nodes commit and acknowledge. This guarantees consistency if a node fails before completion.
Threads provide concurrency within a process by allowing parallel execution. A thread is a flow of execution that has its own program counter, registers, and stack. Threads share code and data segments with other threads in the same process. There are two types: user threads managed by a library and kernel threads managed by the operating system kernel. Kernel threads allow true parallelism but have more overhead than user threads. Multithreading models include many-to-one, one-to-one, and many-to-many depending on how user threads map to kernel threads. Threads improve performance over single-threaded processes and allow for scalability across multiple CPUs.
The document discusses various algorithms for achieving distributed mutual exclusion and process synchronization in distributed systems. It covers centralized, token ring, Ricart-Agrawala, Lamport, and decentralized algorithms. It also discusses election algorithms for selecting a coordinator process, including the Bully algorithm. The key techniques discussed are using logical clocks, message passing, and quorums to achieve mutual exclusion without a single point of failure.
Deadlock in distribute system by saeed siddikSaeed Siddik
The document discusses deadlocks in distributed systems, outlining the four conditions required for a deadlock, strategies to handle deadlocks such as ignoring, detecting, preventing, and avoiding them, and algorithms for centralized deadlock detection and distributed deadlock detection and prevention. It provides examples of resource allocation graphs to illustrate deadlock conditions and explains how distributed deadlock detection and prevention algorithms work.
This document discusses threads and threading models. It defines a thread as the basic unit of CPU utilization consisting of a program counter, stack, and registers. Threads allow for simultaneous execution of tasks within the same process by switching between threads rapidly. There are three main threading models: many-to-one maps many user threads to one kernel thread; one-to-one maps each user thread to its own kernel thread; many-to-many maps user threads to kernel threads in a variable manner. Popular thread libraries include POSIX pthreads and Win32 threads.
Deadlock avoidance methods analyze resource allocation to determine if granting a request would lead to an unsafe state where deadlock could occur. A deadlock happens when multiple processes are waiting indefinitely for resources held by each other in a cyclic dependency. To prevent deadlock, an operating system must have information on current resource availability and allocations, as well as future resource needs. The system only grants requests that will lead to a safe state where there are enough resources for all remaining processes and deadlock is not possible.
This document discusses deadlocks in operating systems. It defines deadlock as when multiple processes are waiting for resources held by each other in a cyclic manner, resulting in none of the processes making progress. It provides examples and describes the four necessary conditions for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It also discusses methods for handling deadlocks, including prevention, avoidance, and recovery techniques like terminating processes or preempting resources.
A deadlock in OS is a situation in which more than one process is blocked because it is holding a resource and also requires some resource that is acquired by some other process. The four necessary conditions for a deadlock situation to occur are mutual exclusion, hold and wait, no preemption and circular
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.
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.
Deadlocks-An Unconditional Waiting Situation in Operating System. We must make sure of This concept well before understanding deep in to Operating System. This PPT will understands you to get how the deadlocks Occur and how can we Detect, avoid and Prevent the deadlocks in Operating Systems.
The document discusses race conditions that occur when multiple processes access shared data concurrently. A critical section is a block of code that only one process can execute at a time to avoid race conditions. The critical section problem aims to ensure only one process is in its critical section at once using mutual exclusion. Mutual exclusion methods like semaphores are used to prevent simultaneous access to shared resources like global variables.
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.
Deadlock detection and recovery by saad symbiansaad symbian
1) Deadlock occurs when there is a cycle of processes where each process is waiting for a resource held by the next process in the cycle.
2) Solutions to deadlock include prevention, avoidance, detection and recovery. Prevention ensures deadlock is impossible through restrictions. Avoidance uses scheduling to steer around deadlock. Detection checks for cycles periodically and recovery kills processes or rolls them back to release resources.
3) Deadlock recovery options include killing all deadlocked processes, killing one at a time to release resources, or rolling processes back to a prior safe state instead of killing them. The process to kill or roll back is chosen based on factors like priority, resources used, and amount of work.
The document discusses memory management techniques used in operating systems. It describes logical vs physical addresses and how relocation registers map logical addresses to physical addresses. It covers contiguous and non-contiguous storage allocation, including paging and segmentation. Paging divides memory into fixed-size frames and pages, using a page table and translation lookaside buffer (TLB) for address translation. Segmentation divides memory into variable-sized segments based on a program's logical structure. Virtual memory and demand paging are also covered, along with page replacement algorithms like FIFO, LRU and optimal replacement.
Salman Ahmed presents on deadlocks in computer systems. A deadlock occurs when two programs are preventing each other from accessing shared resources, causing both programs to cease functioning. Deadlocks happen when processes are holding resources and waiting to acquire more resources, but cannot release the initial resources. There are four main approaches to handling deadlocks: prevention, avoidance, detection, and recovery. Prevention eliminates one of the conditions required for a deadlock, while avoidance allows the system to refuse resource requests to avoid entering a deadlocked state.
This presentation describes about the various memory allocation methods like first fit, best fit and worst fit in memory management and also about fragmentation problem and solution for the problem.
This presentation discusses system calls and provides an overview of their key aspects:
System calls provide an interface between processes and the operating system. They allow programs to request services from the OS like reading/writing files. There are different methods of passing parameters to the OS, such as via registers, parameter blocks, or pushing to the stack. System calls fall into categories including process control, file management, device management, information maintenance, and communication. An example is given of how system calls would be used in a program to copy data between two files.
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.
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
1. There are three methods to handle deadlocks: prevention, avoidance, and detection with recovery.
2. Deadlock prevention ensures that at least one of the necessary conditions for deadlock cannot occur. Deadlock avoidance requires processes to declare maximum resource needs upfront.
3. The Banker's algorithm is a deadlock avoidance technique that dynamically checks the resource allocation state to ensure it remains safe and no circular wait can occur.
Two Phase Commit is a protocol that ensures transactions are either fully committed or aborted across multiple database sites. It uses a coordinator node that initiates a prepare phase where other nodes log transaction details and agree/disagree to commit. If all agree, the coordinator initiates a commit phase where nodes commit and acknowledge. This guarantees consistency if a node fails before completion.
Threads provide concurrency within a process by allowing parallel execution. A thread is a flow of execution that has its own program counter, registers, and stack. Threads share code and data segments with other threads in the same process. There are two types: user threads managed by a library and kernel threads managed by the operating system kernel. Kernel threads allow true parallelism but have more overhead than user threads. Multithreading models include many-to-one, one-to-one, and many-to-many depending on how user threads map to kernel threads. Threads improve performance over single-threaded processes and allow for scalability across multiple CPUs.
The document discusses various algorithms for achieving distributed mutual exclusion and process synchronization in distributed systems. It covers centralized, token ring, Ricart-Agrawala, Lamport, and decentralized algorithms. It also discusses election algorithms for selecting a coordinator process, including the Bully algorithm. The key techniques discussed are using logical clocks, message passing, and quorums to achieve mutual exclusion without a single point of failure.
Deadlock in distribute system by saeed siddikSaeed Siddik
The document discusses deadlocks in distributed systems, outlining the four conditions required for a deadlock, strategies to handle deadlocks such as ignoring, detecting, preventing, and avoiding them, and algorithms for centralized deadlock detection and distributed deadlock detection and prevention. It provides examples of resource allocation graphs to illustrate deadlock conditions and explains how distributed deadlock detection and prevention algorithms work.
This document discusses threads and threading models. It defines a thread as the basic unit of CPU utilization consisting of a program counter, stack, and registers. Threads allow for simultaneous execution of tasks within the same process by switching between threads rapidly. There are three main threading models: many-to-one maps many user threads to one kernel thread; one-to-one maps each user thread to its own kernel thread; many-to-many maps user threads to kernel threads in a variable manner. Popular thread libraries include POSIX pthreads and Win32 threads.
Deadlock avoidance methods analyze resource allocation to determine if granting a request would lead to an unsafe state where deadlock could occur. A deadlock happens when multiple processes are waiting indefinitely for resources held by each other in a cyclic dependency. To prevent deadlock, an operating system must have information on current resource availability and allocations, as well as future resource needs. The system only grants requests that will lead to a safe state where there are enough resources for all remaining processes and deadlock is not possible.
This document discusses deadlocks in operating systems. It defines deadlock as when multiple processes are waiting for resources held by each other in a cyclic manner, resulting in none of the processes making progress. It provides examples and describes the four necessary conditions for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It also discusses methods for handling deadlocks, including prevention, avoidance, and recovery techniques like terminating processes or preempting resources.
A deadlock in OS is a situation in which more than one process is blocked because it is holding a resource and also requires some resource that is acquired by some other process. The four necessary conditions for a deadlock situation to occur are mutual exclusion, hold and wait, no preemption and circular
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 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 different strategies for handling deadlocks in operating systems. It describes the four necessary conditions for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It then explains three general methods for handling deadlocks: prevention, avoidance, and detection with recovery. Prevention ensures a deadlock never occurs by not allowing one of the four conditions. Avoidance allows all conditions but detects unsafe states and avoids them. Detection knows when a deadlock occurs, while recovery regains locked 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.
The document discusses deadlocks in operating systems. It defines deadlocks and explains the four necessary conditions for a deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. It then describes different strategies for handling deadlocks, including prevention, avoidance, detection, and recovery.
This document outlines the key aspects of deadlocks in operating systems. It defines the necessary conditions for a deadlock to occur as mutual exclusion, hold and wait, no preemption, and circular wait. A resource-allocation graph is used to model resource usage, where a cycle indicates a potential deadlock. Deadlocks can be prevented by avoiding one of the necessary conditions, or can be detected using the graph model to identify cycles. Upon detection, processes may need to be terminated or have resources preempted to recover from the deadlock.
Deadlock occurs when multiple processes are blocked waiting for resources held by other processes in the set, resulting in no forward progress. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlock can be handled through prevention, avoidance, detection, and recovery. Prevention ensures one of the four conditions is never satisfied. Avoidance allows resource allocation if it does not lead to an unsafe state. Detection identifies when deadlock occurs. Recovery regains resources by terminating processes or preempting resources.
1) A deadlock occurs when a set of processes are blocked waiting for resources held by other processes in the set, forming a circular wait.
2) For a deadlock to occur, four necessary conditions must be met: mutual exclusion, hold and wait, no preemption, and circular wait.
3) Deadlocks can be prevented by ensuring that at least one of the four conditions is not met, such as allowing resource preemption or requiring processes request all resources before starting. Deadlock avoidance uses algorithms like Banker's Algorithm to prevent unsafe states that could lead to deadlock.
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 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 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 occurs when a set of processes are blocked waiting for resources held by each other in a cyclic manner. There are four necessary conditions for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlock can be prevented by ensuring that at least one condition is never satisfied through methods like resource ordering or avoidance by tracking resource allocation to guarantee safe states. Detection identifies when deadlock has occurred, while recovery requires aborting processes or preempting resources to break cycles.
Deadlocks occur in operating systems when processes are blocked waiting for resources held by other blocked processes, forming a circular wait. There are four conditions for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Deadlocks can be modeled using a resource allocation graph (RAG) with processes and resources as nodes and request/assignment edges. A cycle in the RAG indicates a deadlock. Detection algorithms work by maintaining a wait-for graph (WFG) and periodically searching for cycles, while avoidance methods analyze resource requests to allow only safe sequences.
This document discusses deadlocks in operating systems. It defines deadlock as occurring when each process needs a resource held by another process, resulting in a circular wait. Four necessary conditions for deadlock are outlined: mutual exclusion, hold and wait, no preemption, and circular wait. Methods for handling deadlocks include ignoring them, preventing conditions through resource ordering or avoiding unsafe states, and detecting and recovering from deadlocks.
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.
Deadlocks occur when two or more processes are waiting for resources held by each other, resulting in none of the processes making progress. There are four conditions required for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait. Techniques to prevent deadlocks include attacking each of these conditions, such as not allowing simultaneous access to resources, having processes request all resources up front before starting, allowing preemption of resources, and imposing a global numbering system on resource requests.
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.
Walmart Business+ and Spark Good for Nonprofits.pdfTechSoup
"Learn about all the ways Walmart supports nonprofit organizations.
You will hear from Liz Willett, the Head of Nonprofits, and hear about what Walmart is doing to help nonprofits, including Walmart Business and Spark Good. Walmart Business+ is a new offer for nonprofits that offers discounts and also streamlines nonprofits order and expense tracking, saving time and money.
The webinar may also give some examples on how nonprofits can best leverage Walmart Business+.
The event will cover the following::
Walmart Business + (https://business.walmart.com/plus) is a new shopping experience for nonprofits, schools, and local business customers that connects an exclusive online shopping experience to stores. Benefits include free delivery and shipping, a 'Spend Analytics” feature, special discounts, deals and tax-exempt shopping.
Special TechSoup offer for a free 180 days membership, and up to $150 in discounts on eligible orders.
Spark Good (walmart.com/sparkgood) is a charitable platform that enables nonprofits to receive donations directly from customers and associates.
Answers about how you can do more with Walmart!"
Leveraging Generative AI to Drive Nonprofit InnovationTechSoup
In this webinar, participants learned how to utilize Generative AI to streamline operations and elevate member engagement. Amazon Web Service experts provided a customer specific use cases and dived into low/no-code tools that are quick and easy to deploy through Amazon Web Service (AWS.)
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
In this slide, we'll explore how to set up warehouses and locations in Odoo 17 Inventory. This will help us manage our stock effectively, track inventory levels, and streamline warehouse operations.
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
Throughout his career, he has taken on multifaceted roles, from leading technical project management teams to owning solutions that drive operational excellence. His conscientious and proactive approach is unwavering, whether he is working independently or collaboratively within a team. His ability to connect with colleagues on a personal level underscores his commitment to fostering a harmonious and productive workplace environment.
Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
-------------------------------------------------------------------------------
Find out more about ISO training and certification services
Training: ISO/IEC 27001 Information Security Management System - EN | PECB
ISO/IEC 42001 Artificial Intelligence Management System - EN | PECB
General Data Protection Regulation (GDPR) - Training Courses - EN | PECB
Webinars: https://pecb.com/webinars
Article: https://pecb.com/article
-------------------------------------------------------------------------------
For more information about PECB:
Website: https://pecb.com/
LinkedIn: https://www.linkedin.com/company/pecb/
Facebook: https://www.facebook.com/PECBInternational/
Slideshare: http://www.slideshare.net/PECBCERTIFICATION
1. 1
Dept of Computer Science & Engineering, CEM
Dead locks
Some IO media, such as disks are easily sharable. Multiple processes could be using
the same disk drive for reading & writing.
But we cannot do the same for certain IO media such as a tape drive or a printer. So
they have to be allocated for only one process exclusively. Because of its non-sharable
nature, the user process has to request for the entire device explicitly and the Operating
system has to allocate these IO devices accordingly. Only when the user process gives up a
device explicitly, the Operating system can take it back and add it into the free pool.
Lets us imagine two processes, PA and PB running simultaneously. Half way through,
PA requests the Operating system for a file on the tape drive, and PB requests the Operating
system for the printer. Let us assume that both the requests are granted. After a while PA
request for the printer without giving up the Tape drive. Simultaneously PB requests the tape
drive without giving up the control of printer. In this situation both the process cannot
proceed. PA will wait until PB releases the printer. But that can happen only if PB can
proceeds further and finish off its processing with the printer. And this can happen only if PB
gets the same drive that PA is holding. PB can get the tape drive only if PA can proceed
further and completes its work with the tape drive. That cannot happen too, unless PA gets
the printer which PB is holding. This situation is called ‘deadlock’.
Definition :In a multiprogramming environment, several processes may compete for a finite
number of resources. When a process requests resources and if the resources are not
available at that time, the process enters in a wait state. Waiting processes may never again
change its state, because the resource they have requested are held by other waiting
processes. This situation is called ‘deadlock’.
Graphical Representation of Deadlock
To represent the relation ship between processes and resources, a certain graphical notation
is used.
P1
R1
Fig A
R2 P2
Fig B
Prepared by Shine N Das
2. 2
Dept of Computer Science & Engineering, CEM
In the above figure rectangular boxes as resources named R1 & R2 and circles are processes
P1 & P2. The arrow shows the relationship.
In fig(a), Resources R1 is allocated to process P1 or in other wards P1 holds R1. In fig
(b), processes P2 want Resource R2, but it has not yet got yet. It is waiting for it. The moment
it gets the resources, the direction of the arrows will change.
These graphs are called Direct Resource Allocation Graph (DRAG).
Let us imagine a typical scenario for the deadlock.
• P1 holds R1 but demands R2.
• P2 holds R2 but demands R1.
If we draw a DRAG for this situation it will look like
P1
R1 R2
P2
This is a closed loop, and this situation is called “circular wait” condition.
The same DRAG can also be drawn as shown
P1 P2
R1 R2
If we start from any node and follow all the arrows, we must return to the original
node. That is what makes it a circular wait or deadlock situation.
Conditions for deadlock to occur
There are certain conditions that must be true for a deadlock to occur. Deadlock is a situation
where a process is waiting for another process, which is waiting for another process etc.
Until finally a process in the chain is waiting for the original process- ie, there is a cycle of
Prepared by Shine N Das
3. 3
Dept of Computer Science & Engineering, CEM
processes where each one is waiting for the next one. If the processes are deadlocked, it is
logically impossible for any of them to proceed since they are waiting for each other.
Four necessary conditions for the deadlocks are :
1. Mutual Exclusion: Resources must be allocated to processes at any time in an
exclusive manner and not on a shared basis.
2. Hold and Wait: A process can hold one resource and request another.
3. Circular Wait: A situation can arise in which process P1 holds resource R1 while it
requests resource R2, process P2 holds R2 while it request resource R1.
4. Non-Preemption: If a process holds certain resources no other process should be able
to take them away from it forcibly.
There are three strategies for dealing with deadlocks
Prevention: Place restrictions on resource request so that deadlocks cannot occur
Avoidance: Plan ahead so that you never get into a situation where deadlock is
inevitable.
Detection & Recovery: Detect when deadlock has occurred and recover from it.
I. Deadlock prevention
Deadlock requires the four conditions. If we can prevent anyone of these conditions
from occurring, we can prevent deadlock.
1) Allowing Preemption: - If we can preempt resources, then deadlock is not possible.
All resources can be preempted.
2) Avoiding Mutual Exclusion: - If every resource in the systems were sharable by
multiple processes, deadlock would never occur. However, such sharing is
impracticable in a tape drive, plotter or a printer, which cannot be shared among
several processes. At best, what one can do is to use the spooling techniques for the
printer, where all the printing requests are handled by a separate program when the
spooler is holding the printers.
3) Avoiding Hold & Wait: - If a process acquires all of the resources at one time, then it
will never be in situation where it is holding a resource and waiting for another
resource. This will prevent deadlock.
Prepared by Shine N Das
4. 4
Dept of Computer Science & Engineering, CEM
This situation works and is used in some situation, but it can lead to
insufficient use of resources. Suppose you have a long process that use a tape drive
for the first 10 minutes and then a CD drive for a few seconds. If you have to acquire
them both at the same time, then you will be holding the CD drive for 10 minutes
without using it.
There are two disadvantages: -
(i) Resource utilization may be low: - Since many of the resources may be allocated
but unused for a long period.
(ii) Starvation: - A process that need several popular resources may have to wait
indefinitely, because at least one of the resources that needs is always allocated
to some other processes.
4) Avoiding the circular wait condition: - Circular wait can be eliminated in several
ways. One way is to have a rule saying that a process is entitled only to a single
resource at any moment. It needs a second one; it must release the first one.
Another way to avoid the circular wait is to provide a global numbering of all
the resources.
eg:- 1) Printer
2) Plotter
3) Tape drive
4) CD ROM Drive
Now the rule is this: process can request resources whenever they want to, but all
requests must be made in numerical order. A process may request first a printer, and
then a tape drive, but may not request first a plotter and a printer.
With this rule, the resource allocation graph can never have cycles.
A B Processes
i j Resources
We can get deadlock only if A requests resource j and B requests resource i . Assuming i and
j are distinct resources, they will have different numbers. If i > j then A is not allowed to
requests j . If i < j then B is not allowed to request i. Either way, deadlock is impossible.
Prepared by Shine N Das
5. 5
Dept of Computer Science & Engineering, CEM
II. Detection & Recovery
Detection of deadlock
We will follow a method to detect a deadlock where there are multiple instances for a
resource time. The operating system has to treat each resource separately, regardless of
the time. The operating system in this case, could do the following to detect a deadlock:
i) Number all processes as P0,P1…..PN.
ii) Number each resource using a meaningful coding scheme. For instance the first
character could always be “R” denoting a resource. The second character could
denote the resource type (0=Tape, 1=Printer…etc) and the third character denotes
the resource number or an instance within the type. (Eg. R00, R01, R02…could
denote different tape drive of the same type R10, R11, R12…could be different
printers.)
iii) The operating system maintains two tables as shown below. One is a resource
wise table giving resource type, resource number, allocation status, the process to
which it is allocated and the process that are waiting for it.
Resource Resource Status Process to which Waiting
Type Number allocated Process
R00 Free -- --
Tape
R01 Allocated P1 --
(0)
R02 Allocated P2 P3, P4
Printer R10 Allocated P1 P5
(1)
R20 Allocated P5 P1, P2
Plotter
R21 Free -- --
(2)
R23 Allocated P4 P2, P5
Resource wise Table
Another table is the process wise table giving for each process, the resource held by it
and the resources it is waiting for.
Prepared by Shine N Das
6. 6
Dept of Computer Science & Engineering, CEM
Process Allocated Resource the process
Number Resources is waiting for
P0 -- --
P1 R01, R10 R20
P2 R02 R20
P3 -- R02
P4 R23 R02
P5 R20 R10, R23
Process wise Table
iv) At anytime the OS can use this table to detect a circular wait or a deadlock.
Whenever a resource is demanded by the process, before actually allocating it, the
OS could use the following algorithm to see the allocation can potentially lead to
a deadlock or not.
Algorithm
Step1: Go through the resource wise table one by one (R00, R01,..Etc)
Step2: Ignore entries for free resources (R00, R21)
Step3: For each entries access the process with a resource is allocated (resource R01 is
allocated for process P1)
P1
R01
Step4: Access the process wise table for the process obtained in step3. (P1 in this case)
Step5: From the process wise table obtain the waiting process for the process obtained in
step3. (P1 is waiting for R20)
P1
R01 R20
Step6: Check the process that is allocated for R20 (e.g. P5)
P1 P5
R01 R20
Prepared by Shine N Das
7. 7
Dept of Computer Science & Engineering, CEM
Step7: Check the waiting resources for P5 in the process wise table (e.g. R10, R23)
Step8: The process list now contains P1&P5 and the resource list contain R01, R10, R20 and
R23 for the process P1&P5. This is a circular wait situation and hence a deadlock has been
detected. (P1→R20→P5→R10→P1)
P1 P5
R10 R01 R20 R23
Deadlock Recovery.
Deadlock recovery becomes more complex due to the fact that some processes
definitely loss something in the bargain. Basically there are two approaches to solve this
problem. Suspending a process or killing it.
1) Suspend / Resume a process: -
In this method, a process is selected based on a variety of criteria (low priority,
for instance) and it is suspended for a long time. The resources are reclaimed from
the suspended process and then allocated to other process that is waiting for them.
When one of the waiting processes gets over, the original suspended process is
resumed.
This scheme has several problems in its implementation:
1) Not all OS support the suspend/resume operations due to the overheads involved
in maintaining so many more PCB chains.
2) This strategy cannot e used in any online or real time systems, because, the
response time of some processes then becomes unpredictable, and clearly this is
unacceptable.
3) Suspend / Resume operations are not easy to manage physically /
programmatically for this purpose.
Imagine that a tape is read half way through and then a process holding the tape drive
is suspended. The operator will have to dismount that tape, mount the new tape for
the new process to which the tape drive is now to be allocated. After this new process
Prepared by Shine N Das
8. 8
Dept of Computer Science & Engineering, CEM
is over, when the old processes resumed, the tape for the original process will have to
be mounted and is to be positional exactly.
4) Killing the process:
The OS decides to kill a process and reclaim all its resources after ensuring
that such action will solve the deadlock. This solution is simple; but involves loss of
at least one process.
Solution of a process to be killed again depends on the scheduling policy and
the processes priority. It is safest to kill a lowest priority process, which has just
begun, so that the loss is not very heavy.
III. Dead lock avoidance
Deadlock prevention is concerned with imposing certain restrictions on the
environment or processes, so that deadlocks can never occur. But the OS aims at avoiding a
deadlock rather than preventing one. Deadlock avoidance is concerned with starting with an
environment, where a deadlock is theoretically possible, but by applying some algorithm in
the OS, a dead lock can be avoided.
Bankers Algorithm
The Banker’s algorithm is the best known of the avoidance strategies. The strategy is
modeled after the lending policies employed in a banking system. A bank has a limited
amount of funds- resources- that can be lend to different borrowers- processes. To
accommodate borrowers, the bank may extend a line of credit to its customer. The line of
credit is the maximum claim for resources by the customer.
If the customer borrows some portion of the line of the credit and then requests
additional funds, the first amount borrowed will be paid back to the bank only if the
additional funds are loaned. At the same time the loan dept looks at the funds allocated to all
customers and the hire amount that can be requested by each customer.
The figure below shows the resource allocation graph for the processes. The Banker’s
Algorithm maintains two matrices on a dynamic basis. Matrix A is for resources allocated to
different processes and Matrix B for the resources still needed by different processes. The
Prepared by Shine N Das
9. 9
Dept of Computer Science & Engineering, CEM
resources could be needed one after another or simultaneously. The OS has no way of
knowing this.
P0 P1 P2
P3
Tape drives Printers Plotters
Current Allocation Outstanding Request
Process R1 R2 R3 R1 R2 R3
Tapes Printers Plotters Tapes Printers Plotters
P0 2 0 0 1 0 0
P1 0 1 0 1 1 0
P2 1 2 1 2 1 1
P3 1 0 1 1 1 1
Matrix A Matrix B
Resources Resources
assigned required
Vectors
Total resources (T) = 543
Held resources (H) = 432
Free resources (F) = 111
Matrix A shows that process P0 is holding 2 tape drives at a given time at the same
movement, P1 is holding 1 printer and so on. If we add these figures vertically we get a
vector of held resources (H) = 432.
This says that at a given moment, total resources held by various processes are 4
Tape drives, 3 printers and 4 plotters. By the same logic figure show the vector for the Total
Resources (T) is 543. This means that in the whole system 5 Tape drives 4 Printers and 3
Prepared by Shine N Das
10. 10
Dept of Computer Science & Engineering, CEM
Plotters. These resources are made known to the OS in the time of system generation. By
subtracting H from T columnwise we get a vector (F) of Free Resources = 111. This means
that the resources available to the OS for further allocation are: 1 Tape drive 1 printer & 1
Plotter.
Matrix B gives, additional resources that are expected to be in due course during the
execution of these processes. For instance, P2 will require 2 tape drives, 1 printer and 1
plotter in addition to the resources already held by it. It means P2 requires, 1+2 =3 tape
drives, 2+1 = 3 printers and 1+1= 2 plotters. If the vector of all resources required by the
processes is less than the vector (T) for each of the resources (eg: 332 < 543) there will not
be any deadlock. However if that is not so, a deadlock has to be avoided.
Banker’s Algorithm
Step 1: - Each process declares the total required resources to the OS at the beginning. The
OS puts these figures in Matrix B (resources required for completion) against each process.
For a newly created process the rows in Matrix A is fully zero because no resources are yet
assigned for that process.
Eg: At the beginning of process P2, the figures for the rows for P2 in matrix A will be
all 0, and those in Matrix will be 3,3 and 2.
Step 2: - When a process requests the OS for a resource, the OS finds out whether the
resource is free and whether it can be allocated by using the vector F. if it can be allocated,
the OS does so, and updates matrix A by adding 1 to the appropriate slot. It simultaneously
subtract 1 from the corresponding slot of matrix B
Eg: - if the OS allocates tape drive to processP2, the rows for P2 in the matrix A will
become 1,0,0 and rows with Matrix B will correspondingly become 2,3and 2.
Step 3: - Whenever a process makes a request to OS for any resource, before making the
actual allocation, it makes an imaginary allocation using bankers algorithm to ensure that
there need not be a deadlock. The OS actually allocates the resource only after ensuring this.
If it finds that there can be a deadlock after imaginary allocation, it postpones the decision to
allocate that resource.
During the imaginary allocation the OS conclude about the safe and unsafe state in
the following manner.
It looks at vector F and each row of the Matrix B. It compares them on a vector to
vector basis ie, within the vector, it compares each digit separately to conclude whether all
the resources that a process is going to need to complete are available at this point or not.
Prepared by Shine N Das
11. 11
Dept of Computer Science & Engineering, CEM
Eg: - Figure shows F= 111. If the OS decides to allocate all needed resources to P0, it
compares 111 with 100, (111> 100), on a vector basis, and P0 can go for completion.
Similarly the OS decided to allocate resources to P1. P1 can complete (111 >100) etc. the
rows for P2 is 211, therefore P2 cannot complete unless there is one more tape drive is
available (111 < 211).
For each request for any resources by a process the operating system goes through
all these trial or imaginary allocations and updations, and if it finds that after the trial
allocation, the state of the system would be ‘safe’, it does ahead and makes an allocation in
real sense.
Example 1
Suppose process P1 requests for 1 tape drive when the resources allocated to various
processes are given in the fig. The OS has to decide whether to grant this request or not.
The Bankers Algorithm proceeds to determine this as follows.
• If a tape drive is allocated to P1, F will become 011 and the resources still required
for P1 in matrix B will become 010.
• If P1 is given all the resources it needs to complete, the rows for assigned resources
of P1 in matrix A will become 120 and after this allocation F will become 001.
• At the end of the execution of P1, all the resources used by P1 will become free and F
will become 120 + 001 =121. we can now erase the row P1 from both the matrices
indicating that this is how the matrices will look if P1 is granted its first request.
• We repeat the same step with other rows. For instance now F=121. Therefore the OS
will have sufficient resources to complete either P0 or P3 but not P2. Let us take P0,
assuming that all the required resources are allocated to P0 one by one. The rows for
P0 in matrix A become 300 and matrix B becomes 000. F at this point becomes
121 – 100 = 021. If P0 is now allocated to completion, all the resources held by P0
will be returned to F and F becomes 021 + 300 = 321.
• Now either P2 or P3 can be chosen for this ‘trial allocation’. Let us assume that P3 is
allocated. The recourse required by P3 are111. Therefore after trial allocation, rows of
P3 in Matrix A becomes 212 and Matrix B becomes 000. The value of F become now
321 – 111 = 210. After the process completion the resources are returned back to F
and F becomes 210 + 212 = 422.
Prepared by Shine N Das
12. 12
Dept of Computer Science & Engineering, CEM
• At the end P2 will be allocated and completed. At this point resources allocated to P2
is 332, and F would be 422 – 211. In the end, resources will be returned to the free
pool. Therefore F = 322 + 211 = 543. This is the same as the total resource vector T
that are known to the system.
Prepared by Shine N Das