ch18 - perating System Concepts with Java 7 th Edition, Nov...

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Unformatted text preview: perating System Concepts with Java 7 th Edition, Nov 15, 2006 Silberschatz, Galvin and Gagne 2007 Chapter 18: Distributed Coordination 18.2 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Chapter 18 Distributed Coordination Event Ordering Mutual Exclusion Atomicity Concurrency Control Deadlock Handling Election Algorithms Reaching Agreement 18.3 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Chapter Objectives To describe various methods for achieving mutual exclusion in a distributed system To explain how atomic transactions can be implemented in a distributed system To show how some of the concurrency-control schemes discussed in Chapter 6 can be modified for use in a distributed environment To present schemes for handling deadlock prevention, deadlock avoidance, and deadlock detection in a distributed system 18.4 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Event Ordering Happened-before relation (denoted by ) If A and B are events in the same process, and A was executed before B , then A B If A is the event of sending a message by one process and B is the event of receiving that message by another process, then A B If A B and B C then A C 18.5 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Relative Time for Three Concurrent Processes 18.6 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Implementation of Associate a timestamp with each system event Require that for every pair of events A and B, if A B, then the timestamp of A is less than the timestamp of B Within each process Pi a logical clock , LCi is associated The logical clock can be implemented as a simple counter that is incremented between any two successive events executed within a process Logical clock is monotonically increasing A process advances its logical clock when it receives a message whose timestamp is greater than the current value of its logical clock If the timestamps of two events A and B are the same, then the events are concurrent We may use the process identity numbers to break ties and to create a total ordering 18.7 Silberschatz, Galvin and Gagne 2007 Operating System Concepts with Java 7 th Edition, Nov 15, 2006 Distributed Mutual Exclusion (DME) Assumptions The system consists of n processes; each process P i resides at a different processor Each process has a critical section that requires mutual exclusion Requirement If P i is executing in its critical section, then no other process P j is executing in its critical section We present two algorithms to ensure the mutual exclusion execution of processes in their critical sections 18.8 Silberschatz, Galvin and Gagne 2007...
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ch18 - perating System Concepts with Java 7 th Edition, Nov...

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