ch07 - Chapter 7 Deadlocks Chapter 7 Deadlocks s The...

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Chapter 7:  Deadlocks Chapter 7:  Deadlocks
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7.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter 7:  Deadlocks Chapter 7:  Deadlocks The Deadlock Problem System Model Deadlock Characterization Methods for Handling Deadlocks Deadlock Prevention Deadlock Avoidance Deadlock Detection  Recovery from Deadlock 
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7.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter Objectives 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.
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7.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts The Deadlock Problem The Deadlock Problem A set of blocked processes each holding a resource and waiting to  acquire a resource held by another process in the set. Example  System has 2 tape drives. P 1  and  P 2  each hold one tape drive and each needs another  one. Example  semaphores  A  and  B , initialized to 1      P 0     P 1 wait (A); wait(B) wait (B); wait(A)
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7.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Bridge Crossing Example Bridge Crossing Example Traffic only in one direction. Each section of a bridge can be viewed as a resource. If a deadlock occurs, it can be resolved if one car backs up  (preempt resources and rollback). Several cars may have to be backed up if a deadlock  occurs. Starvation is possible.
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7.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts System Model System Model Resource types  R 1 R 2 , . . .,  R m CPU cycles, memory space, I/O devices Each resource type  R i  has  W i  instances. Each process utilizes a resource as follows: request  use  release
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7.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Deadlock Characterization Deadlock Characterization 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 { P 0 P 1 , …,  P 0 } of waiting  processes such that  P is waiting for a resource that is held  by  P 1 P 1  is waiting for a resource that is held by  P 2 , …,  P n –1  is waiting for a resource that is held by  P n , and  P 0  is waiting for a resource that is held by  P 0 .
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ch07 - Chapter 7 Deadlocks Chapter 7 Deadlocks s The...

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