Lecture "Operating system - Chapter 3: Deadlocks" has contents: Resource, introduction to deadlocks, the ostrich algorithm, deadlock detection and recovery, deadlock avoidance, deadlock prevention, other issues. | Deadlocks Chapter 3 . Resource . Introduction to deadlocks . The ostrich algorithm . Deadlock detection and recovery . Deadlock avoidance . Deadlock prevention . Other issues Resources Examples of computer resources printers tape drives tables Processes need access to resources in reasonable order Suppose a process holds resource A and requests resource B at same time another process holds B and requests A both are blocked and remain so Resources (1) Deadlocks occur when processes are granted exclusive access to devices we refer to these devices generally as resources Preemptable resources can be taken away from a process with no ill effects Nonpreemptable resources will cause the process to fail if taken away Resources (2) Sequence of events required to use a resource request the resource use the resource release the resource Must wait if request is denied requesting process may be blocked may fail with error code Introduction to Deadlocks . | Deadlocks Chapter 3 . Resource . Introduction to deadlocks . The ostrich algorithm . Deadlock detection and recovery . Deadlock avoidance . Deadlock prevention . Other issues Resources Examples of computer resources printers tape drives tables Processes need access to resources in reasonable order Suppose a process holds resource A and requests resource B at same time another process holds B and requests A both are blocked and remain so Resources (1) Deadlocks occur when processes are granted exclusive access to devices we refer to these devices generally as resources Preemptable resources can be taken away from a process with no ill effects Nonpreemptable resources will cause the process to fail if taken away Resources (2) Sequence of events required to use a resource request the resource use the resource release the resource Must wait if request is denied requesting process may be blocked may fail with error code Introduction to Deadlocks Formal definition : A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause Usually the event is release of a currently held resource None of the processes can run release resources be awakened Four Conditions for Deadlock Mutual exclusion condition each resource assigned to 1 process or is available Hold and wait condition process holding resources can request additional No preemption condition previously granted resources cannot forcibly taken away Circular wait condition must be a circular chain of 2 or more processes each is waiting for resource held by next member of the chain Deadlock Modeling (2) Modeled with directed graphs resource R assigned to process A process B is requesting/waiting for resource S process C and D are in deadlock over resources T and U Deadlock Modeling (3) Strategies for dealing with Deadlocks just ignore the problem altogether detection and recovery dynamic avoidance .
