Lecture Operating systems: A concept-based approach (2/e): Chapter 17 - Dhamdhere

PROPRIETARY MATERIAL. © 2007 The McGraw­Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw­Hill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission. Chapter 17: Distributed Control Algorithms Dhamdhere: Operating Systems— A Concept­Based Approach , 2 ed Slide No: 1 Copyright © 2008 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 computers – Scheduling * Perform load balancing to ensure uniform loading of computers – Termination detection * Check whether all processes of a computation, which may operate in different computers, have completed – Election * Elect a coordinator for a privileged function like resource allocation Chapter 17: Distributed Control Algorithms Dhamdhere: Operating Systems— A Concept­Based Approach , 2 ed Slide No: 2 Copyright © 2008 Nature of a distributed control algorithm • A distributed control function offers services to both system and user processes – It operates in parallel with its clients • Following terminology is used to differentiate between the distributed control algorithm and its clients – Basic computation: Operation of a client * Interprocess messages used by it are called basic messages – Control computation: Operation of the control algorithm * Interprocess messages exchanged in the control computation are called control messages – Basic part and control part of a process * Participate in the basic and control computations, respectively Chapter 17: Distributed Control Algorithms Dhamdhere: Operating Systems— A Concept­Based Approach , 2 ed Slide No: 3 Copyright © 2008 Basic and control parts of a process Pi • The basic part of Pi interacts with basic parts of other processes through basic messages; analogously for control part of Pi • The control part provides services such as resource allocation to the basic part Chapter 17: Distributed Control Algorithms Dhamdhere: Operating Systems— A Concept­Based Approach , 2 ed Slide No: 4 Copyright © 2008 Correctness of a distributed control algorithm • Processes of a distributed control algorithm exchange control data and coordinate through control messages – New correctness issues arise because * Exchange of control messages incurs delays Control data used in processes may become stale or may appear inconsistent – Hence correctness has two new facets * Liveness The algorithm must eventually perform the correct action * Safety The algorithm must not perform wrong actions Chapter 17: Distributed Control Algorithms Dhamdhere: Operating Systems— A Concept­Based Approach , 2 ed Slide No: 5 Copyright © 2008 ... - tailieumienphi.vn