Deadlock in Operating Systems

A situation where two or more processes are blocked indefinitely, each waiting for a resource held by another process.

A resource that can be used by only one process at a time. Examples: printer, file, CPU.

The state when a process is waiting for a resource that is currently held by another process.

The state when a process requests a resource that is currently held by another process.

An instance where a process is stuck waiting for a resource, but the resource is already being occupied by another process that is waiting for a resource held by the first process.

Deadlock occurs when all four conditions are met: mutual exclusion, hold and wait, no preemption, and circular wait.

Techniques that aim to prevent deadlock from occurring in the first place. Examples: preventing circular wait, allocating resources based on priorities, and using preemption.

Techniques that break the deadlock after it happens. Examples: preemption, rollback, and resource allocation.

A condition where a process is holding onto a resource while waiting for another, preventing other processes from accessing it.

A process cannot be forcibly removed from a resource it is holding.

A directed graph that visually represents resources, processes, and the relationships between them. It helps to identify potential deadlocks.

A cycle in the Resource-Allocation Graph indicates a potential deadlock. It doesn't guarantee a deadlock, but it raises the possibility.

The ability to share a resource amongst multiple processes. Some resources can be shared concurrently while others have limitations on the number of processes that can access them.

The maximum number of instances of each resource type that a process can request.

The number of instances of each resource type that a process is currently holding.

The difference between the maximum allocation and the allocated resources, representing the number of instances of each resource type that a process still needs to complete its task.

The number of instances of each resource type that are currently available in the system.

The Banker's Algorithm calculates the 'Need' by subtracting the 'Allocated Resources' from the 'Max Allocation' for each process, ensuring that all processes have the resources they need to complete their tasks.

Mutual exclusion is a condition where only one process can access a resource at a time.

A hardware solution to eliminate mutual exclusion is to increase the number of devices, giving multiple processes simultaneous access.

Deadlock occurs when two or more processes are blocked indefinitely, each waiting for a resource held by another process.

To prevent hold and wait, ensure that a process requests all necessary resources before starting execution

Another way to prevent hold and wait is to disallow processes from requesting resources while holding any existing resources.

Low resource utilization can occur because a system resource is held unnecessarily even when it's not in use, potentially leading to starvation.

Preemption, where a process gives up a resource it holds, can prevent deadlock.

Requiring resources to be requested and allocated in a specific order eliminates circular waiting, a key condition causing deadlock.

In the Banker's Algorithm, the 'Need' matrix represents the remaining resources each process requires to complete its task. It's calculated by subtracting the current allocation from the maximum resource requirement of each process.

The 'Avail' matrix in the Banker's Algorithm represents the currently available resources in the system. It is calculated by subtracting the total allocated resources from the total available resources.

The Banker's Algorithm checks if a request can be granted safely by simulating the allocation and checking if the system remains in a safe state. A safe state allows all processes to complete their tasks without deadlocking.

A safe state in the Banker's Algorithm means that there's a sequence of process executions where each process can complete its task without waiting for resources held by other processes. The system won't deadlock.

If a resource request leads to an unsafe state, it means that the system could potentially enter a deadlock scenario if other processes request resources that are now unavailable. Therefore, the request is rejected to prevent a deadlock.

The Banker's Algorithm aims to prevent deadlocks by ensuring that any resource allocation sequence leads to a safe state. It does this by carefully evaluating requests and ensuring that granting them won't lead to a deadlock.

The 'Available' vector in the Banker's Algorithm is a dynamic vector that reflects the current state of resources available in the system. As processes release resources, the 'Available' vector is updated to reflect this change.

An unsafe state indicates a possibility of reaching a deadlock. It's not a deadlock situation itself, but rather a potential precursor. It's a state where the system may reach a deadlock if certain resources are requested by other processes.

A system that doesn't prevent or avoid deadlock needs a way to detect the deadlock and recover from it.

A graphical approach using a resource allocation graph can be used to detect deadlocks when there is only one instance of each resource. This graph shows how resources are allocated among processes.

By redrawing the request edges to point to the process holding the requested resource, we can create a graph where a cycle indicates a potential deadlock.

The Wait-for Graph helps us understand dependencies between processes that are waiting for resources. A cycle in this graph shows that processes are perpetually waiting for each other, indicating a deadlock.

When dealing with multiple instances of each resource, we use algorithms like the Banker's Algorithm to detect deadlocks. This algorithm tracks the allocation and needs of resources for each process.

The Banker's Algorithm is a systematic approach that uses vectors like Available, Allocation, Need, and Finish to check resource requests. The algorithm aims to ensure resource availability and prevent deadlocks.

Deadlock detection algorithms are crucial for ensuring system stability and avoiding disruptions. These algorithms are often used in conjunction with deadlock prevention or avoidance techniques to provide a comprehensive solution for managing resource allocation.