Deadlock Modeling 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 Computer Engineering Department - MEFGI10 11. Each process utilizes a resource as follows: request use releaseComputer Engineering Department - MEFGI9 10. , Rm CPU cycles, memory space, I/O devices Each resource type Ri has Wi instances. Computer Engineering Department - MEFGI8 9. Circular wait: there exists a set of waiting processes such that P0 is waiting for a resource that is held by P1, P1 is waiting for a resource that is held by P2,, Pn1 is waiting for a resource that is held by Pn, and P0 is waiting for a resource that is held by P0. then and then only No preemption: a resource can be released only voluntarily deadlock arise by the process holding it, after that process has completed its task. Four conditions Hold and wait: a process holding at least one resource is waiting to acquire hold additional resources held by other simultaneously processes. Deadlock Characterization Mutual exclusion: only one process at a time can use a resource. Technical Terms 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 Computer Engineering Department - MEFGI7 8. Computer Engineering Department - MEFGI6 7. Several cars may have to be backed up if a deadlock occurs. If a deadlock occurs, it can be resolved if one car backs up (preempt resources and rollback). Each section of a bridge can be viewed as a resource. Deadlock Continue Traffic only in one direction. Computer Engineering Department - MEFGI5 6. P1 and P2 each hold one tape drive and each needs another one. What is Deadlock A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set. Technical IssueComputer Engineering Department - MEFGI4 5. MotivationComputer Engineering Department - MEFGI3 4. Content Deadlock Problem Deadlock Characterization Deadlock Detection Deadlock recovery Deadlock avoidance Deadlock Prevention.Computer Engineering Department - MEFGI2 3. Email: Slides: Computer Engineering Department - MEFGI1Ģ. 1.Module 4 - Deadlock Hemang Kothari Assistant Professor Computer Engineering Department MEFGI, Rajkot.Resource Allocation Graph contains the whole information related to all processes those are hold by few resources otherwise getting to wait for some resources. In the Resource Allocation Graph, to represent of all states of system in the graphically form. Several instance of a resources type – To use Banker’s Algorithm Resource Allocation Graph.One instance of a resources type – To use a Resource Allocation Graph.Deadlock Avoidance can be solved by two different algorithms, such as – If ensure that system will never going to enter an unsafe state, then Avoidance is getting. ![]() ![]() If system is getting in the unsafe state, then may be occur deadlock.If system is getting in the safe state, then does not happen deadlock.If Pi terminates, then Pi+1 can get its required resources, and so on. ![]()
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