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Lecture Operating system concepts (9th Ed) - Chapter 7: Deadlocks

After studying this chapter you will be able to develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks; to present a number of different methods for preventing or avoiding deadlocks in a computer system. | Chapter 7: Deadlocks Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013 Chapter 7: Deadlocks System Model Deadlock Characterization Methods for Handling Deadlocks Deadlock Prevention Deadlock Avoidance Deadlock Detection Recovery from Deadlock Operating System Concepts – 9th Edition 7.2 Silberschatz, Galvin and Gagne ©2013 Chapter Objectives To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks To present a number of different methods for preventing or avoiding deadlocks in a computer system Operating System Concepts – 9th Edition 7.3 Silberschatz, Galvin and Gagne ©2013 System Model System consists of resources Resource types R1, R2, . . ., Rm CPU cycles, memory space, I/O devices Each resource type Ri has Wi instances. Each process utilizes a resource as follows: request use release Operating System Concepts – 9th Edition 7.4 Silberschatz, Galvin and Gagne ©2013 Deadlock Characterization Deadlock can arise if four conditions hold simultaneously. Mutual exclusion: only one process at a time can use a resource Hold and wait: a process holding at least one resource is waiting to acquire additional resources held by other processes No preemption: a resource can be released only voluntarily by the process holding it, after that process has completed its task Circular wait: there exists a set {P0, P1, , Pn} 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, , Pn–1 is waiting for a resource that is held by Pn, and Pn is waiting for a resource that is held by P0. Operating System Concepts – 9th Edition 7.5 Silberschatz, Galvin and Gagne .