A deadlock is a situation in which processes wait for one another indefinitely due to resource sharing or synchronization. This chapter discusses how deadlocks can arise and how an OS performs deadlock handling to ensure an absence of deadlocks, either through detection and resolution of deadlocks, or through resource allocation policies that perform deadlock prevention or deadlock avoidance. | Chapter 8 Deadlocks Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Introduction What is a Deadlock? Deadlocks in Resource Allocation Handling Deadlocks Deadlock Detection and Resolution Deadlock Prevention Deadlock Avoidance Characterization of Resource Deadlocks by Graph Models Deadlock Handling in Practice 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere What is a Deadlock? Resource deadlock primary concern of OS Pi, Pj are deadlocked after their second requests Deadlocks can also arise in synchronization and message communication user concern 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Deadlocks in Resource Allocation OS may contain several resources of a kind Resource unit refers to a resource of a specific kind Resource class to refers to the collection of all resource units of a kind Resource allocation in a system entails three . | Chapter 8 Deadlocks Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Introduction What is a Deadlock? Deadlocks in Resource Allocation Handling Deadlocks Deadlock Detection and Resolution Deadlock Prevention Deadlock Avoidance Characterization of Resource Deadlocks by Graph Models Deadlock Handling in Practice 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere What is a Deadlock? Resource deadlock primary concern of OS Pi, Pj are deadlocked after their second requests Deadlocks can also arise in synchronization and message communication user concern 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Deadlocks in Resource Allocation OS may contain several resources of a kind Resource unit refers to a resource of a specific kind Resource class to refers to the collection of all resource units of a kind Resource allocation in a system entails three kinds of events: Request for the resource Actual allocation of the resource Release of the resource Released resource can be allocated to another process 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Deadlocks in Resource Allocation (continued) 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Conditions for a Resource Deadlock Another condition is also essential for deadlocks: No withdrawal of resource requests: A process blocked on a resource request cannot withdraw it 8. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Modeling the Resource Allocation State (Resource) allocation state: Information about resources allocated to processes and about pending resource requests Used to determine whether a set of processes is deadlocked Two kinds of models are used to represent the allocation state of a .
