L8.sp11 - Distributed Systems Distributed Systems CS 425 /...

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Distributed Systems CS 425 / CSE 424 / ECE 428 Distributed Systems CS 425 / CSE 424 / ECE 428 Mutual Exclusion Reading: Sections 12.2 010, I . Gupta, K. Nahrtstedt, S. Mitra, N. Vaidya, M. T. Harandi, J. Hou
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Why Mutual Exclusion? Why Mutual Exclusion? Bank’s Servers in the Cloud : Think of two simultaneous deposits of $10,000 into your bank account, each from one ATM. Both ATMs read initial amount of $1000 concurrently from the bank’s cloud server Both ATMs add $10,000 to this amount (locally at the ATM) Both write the final amount to the server What’s wrong?
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Bank’s Servers in the Cloud : Think of two simultaneous deposits of $10,000 into your bank account, each from one ATM. Both ATMs read initial amount of $1000 concurrently from the bank’s cloud server Both ATMs add $10,000 to this amount (locally at the ATM) Both write the final amount to the server What’s wrong? The ATMs need mutually exclusive access to your account entry at the server (or, to executing the code that modifies the account entry) Why Mutual Exclusion? Why Mutual Exclusion?
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Critical section problem: Piece of code (at all clients) for which we need to ensure there is at most one client executing it at any point of time. Solutions: Semaphores, mutexes, etc. in single-node operating systems Message-passing-based protocols in distributed systems: enter() the critical section AccessResource() in the critical section exit() the critical section Distributed mutual exclusion requirements: Safety – At most one process may execute in CS at any time Liveness – Every request for a CS is eventually granted Ordering (desirable) – Requests are granted in the order they were made Mutual Exclusion Mutual Exclusion
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Distributed Mutual Exclusion: Performance Evaluation Criteria Distributed Mutual Exclusion: Performance Evaluation Criteria Overhead : the total number of messages sent in each entry and exit operation.
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This note was uploaded on 02/08/2012 for the course ECE 428 taught by Professor Hu during the Spring '08 term at University of Illinois, Urbana Champaign.

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L8.sp11 - Distributed Systems Distributed Systems CS 425 /...

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