CS345 18 - DME

CS345 18 - DME - CS 345 Operating Systems Fall 2010 Section...

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BYU CS 345 Distributed Mutual Exclusion 1 CS 345 – Operating Systems Fall 2010 Section 001 , 1:00 – 1:50 pm MWF Section 002 , 2:00 – 2:50 pm MWF Instructor: Paul Roper Office: TMCB 3370, 422-8149 Email: proper@cs.byu.edu Office Hours: 9:30 – 10:50 am MWF
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BYU CS 345 Distributed Mutual Exclusion 2 Distributed Mutual Exclusion Chapter 18 – Distributed Process Management http://www.williamstallings.com/OS/OS6e.html
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BYU CS 345 Distributed Mutual Exclusion 3 Topics to Cover… Distributed Systems Event Ordering Distributed Mutual Exclusion Objectives
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BYU CS 345 Distributed Mutual Exclusion 4 Distributed Systems Distribute processing across network nodes to form a single computing environment. Concurrent processes that need to synchronize Distributed coordination (finance, transactions, …) Distributed deadlock detection Load balancing Distributed shared memory Network Memory P 0 P 1 P 2 P 3 Memory Memory Memory Distributed Systems
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BYU CS 345 Distributed Mutual Exclusion 5 Distributed Coordination Synchronization on a single system is relatively easy semaphores monitors Modern distributed systems No shared memory. (This distinguishes distributed systems from multiprocessor systems.) No global clock. Each processor has its own clock. Processes communicate by a reliable message protocol. How do you synchronize in a distributed system? Event Ordering
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BYU CS 345 Distributed Mutual Exclusion 6 p 0 p 1 p 2 p 3 p 4 q 0 q 1 q 2 q 3 q 4 r 0 r 1 P Q R time Processes: events messages P1 Q2 R0 Q4 P 1 R 0 ? r 2 r 3 r 4 Event Ordering
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BYU CS 345 Distributed Mutual Exclusion 7 Distributed Mutual Exclusion DME algorithms to consider Centralized Token passing Election Consensus Fully distributed In each case, assume: n processes only one process may be in critical section DME
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BYU CS 345 Distributed Mutual Exclusion 8 Centralized Designate a process as the coordinator coordinates all access to critical sections To enter critical section send request message to coordinator wait for reply then enter critical section send release when done Coordinator Queue incoming requests send reply to first in queue and wait for release DME
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BYU CS 345 Distributed Mutual Exclusion
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CS345 18 - DME - CS 345 Operating Systems Fall 2010 Section...

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