Chapter 7 - Deadlocks

Chapter 7: Deadlocks ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Chapter Objectives ,[object Object],[object Object]

The Deadlock Problem ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Bridge Crossing Example ,[object Object],[object Object],[object Object],[object Object],[object Object]

System Model ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Deadlock Characterization ,[object Object],[object Object],[object Object],[object Object],[object Object],Deadlock can arise if four conditions hold simultaneously.

Resource-Allocation Graph ,[object Object],[object Object],[object Object],[object Object],[object Object],A set of vertices V and a set of edges E .

Resource-Allocation Graph (Cont.) ,[object Object],[object Object],[object Object],[object Object],P i P i R j R j

Example of a Resource Allocation Graph

Resource Allocation Graph With A Deadlock

Graph With A Cycle But No Deadlock

Basic Facts ,[object Object],[object Object],[object Object],[object Object]

Methods for Handling Deadlocks ,[object Object],[object Object],[object Object]

Deadlock Prevention ,[object Object],[object Object],[object Object],[object Object],Restrain the ways request can be made.

Deadlock Prevention (Cont.) ,[object Object],[object Object],[object Object],[object Object],[object Object]

Deadlock Avoidance ,[object Object],[object Object],[object Object],Requires that the system has some additional a priori information available.

Safe State ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Basic Facts ,[object Object],[object Object],[object Object]

Avoidance algorithms ,[object Object],[object Object]

Resource-Allocation Graph Scheme ,[object Object],[object Object],[object Object],[object Object],[object Object]

Unsafe State In Resource-Allocation Graph

Resource-Allocation Graph Algorithm ,[object Object],[object Object]

Banker’s Algorithm ,[object Object],[object Object],[object Object],[object Object]

Data Structures for the Banker’s Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],Let n = number of processes, and m = number of resources types.

Safety Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Resource-Request Algorithm for Process P i ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example of Banker’s Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example (Cont.) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example: P 1 Request (1,0,2) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Deadlock Detection ,[object Object],[object Object],[object Object]

Single Instance of Each Resource Type ,[object Object],[object Object],[object Object],[object Object],[object Object]

Resource-Allocation Graph and Wait-for Graph Resource-Allocation Graph Corresponding wait-for graph

Several Instances of a Resource Type ,[object Object],[object Object],[object Object]

Detection Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Detection Algorithm (Cont.) ,[object Object],[object Object],Algorithm requires an order of O( m x n 2) operations to detect whether the system is in deadlocked state .

Example of Detection Algorithm ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example (Cont.) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Detection-Algorithm Usage ,[object Object],[object Object],[object Object],[object Object],[object Object]

Recovery from Deadlock: Process Termination ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Recovery from Deadlock: Resource Preemption ,[object Object],[object Object],[object Object]

Chapter 7 - Deadlocks

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Chapter 7 - Deadlocks