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Chapter 18 Distributed Control Algorithms
Copyright © 2008
Introduction
• Operation of Distributed Control Algorithms
• Correctness of Distributed Control Algorithms • Distributed Mutual Exclusion
• Distributed Deadlock Handling
• Distributed Scheduling Algorithms • Distributed Termination Detection • Election Algorithms
• Practical Issues in Using Distributed Control Algorithms
Operating Systems, by Dhananjay Dhamdherehamdhere 18.2 2
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OS Control Functions in a Distributed Environment
• Special features of distributed OS control functions – Mutual exclusion
• Involves synchronization of processes in different computers – Deadlock handling
• Deadlocks may involve use of resources in different hosts – Scheduling
• Perform load balancing for comparable loading of computers – Termination detection
• Check whether all processes of a computation, which may operate in different computers, have completed
– Election
• Elect coordinator for a privileged function
Operating Systems, by Dhananjay Dhamdherehamdhere 18.3 3
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Operation of Distributed Control Algorithms (continued)
• A distributed control algorithm operates in parallel with its clients, so that it can respond readily to events related to its service
– Each process has a control part and a basic part
Operating Systems, by Dhananjay Dhamdherehamdhere 18.4 4
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Correctness of Distributed Control Algorithms
• Algorithm correctness has two facets:
– Liveness: eventually performs correct actions • i.e., without indefinite delays
– Safety: does not perform wrong actions
• Proving correctness of a distributed algorithm is a complex task
Operating Systems, by Dhananjay Dhamdherehamdhere 18.5 5
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