Week 4_ Synchronization

Week 4_ Synchronization - Synchronization in Distributed...

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Synchronization in Distributed Systems CS-4513 D-term 2008 1 Synchronization in Distributed Systems CS-4513 Distributed Computing Systems (Slides include materials from Operating System Concepts , 7 th ed., by Silbershatz, Galvin, & Gagne, Distributed Systems: Principles & Paradigms , 2 nd ed. By Tanenbaum and Van Steen, and Modern Operating Systems , 2 nd ed., by Tanenbaum)
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Synchronization in Distributed Systems CS-4513 D-term 2008 2 Issue Synchronization within one system is hard enough Semaphores Messages Monitors Synchronization among processes in a distributed system is much harder
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Synchronization in Distributed Systems CS-4513 D-term 2008 3 Example File locking in NFS Not supported directly within NFS v.3 Need lockmanager service to supplement NFS
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Synchronization in Distributed Systems CS-4513 D-term 2008 4 What about using Time ? make recompiles if foo.c is newer than foo.o Scenario make on machine A to build foo.o Test on machine B ; find and fix a bug in foo.c Re-run make on machine B Nothing happens! Why?
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Synchronization in Distributed Systems CS-4513 D-term 2008 5 Synchronizing Time on Distributed Computers See Tanenbaum & Van Steen, §6.1.1, 6.1.2 for descriptions of Solar Time International Atomic Time GPS, etc. §6.1.3 for Clock Synchronization algorithms
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Synchronization in Distributed Systems CS-4513 D-term 2008 6 NTP (Network Time Protocol) A requests time of B at its own T 1 B receives request at its T 2 , records B responds at its T 3 , sending values of T 2 and T 3 A receives response at its T 4 Question: what is θ = T B – T A ? A B T 1 T 2 T 3 T 4
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Synchronization in Distributed Systems CS-4513 D-term 2008 7 NTP (Network Time Protocol) Question: what is θ = T B – T A ? Assume transit time is approximately the same both ways Assume that B is the time server that A wants to synchronize to A B T 1 T 2 T 3 T 4
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Synchronization in Distributed Systems CS-4513 D-term 2008 8 NTP (Network Time Protocol) A knows ( T 4 – T 1 ) from its own clock
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This note was uploaded on 11/15/2011 for the course ECKOW 123 taught by Professor Riuyt during the Spring '11 term at University of Damascus.

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Week 4_ Synchronization - Synchronization in Distributed...

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