Lecture6 - COT 5611 Operating Systems Design Principles...

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COT 5611 Operating Systems Design Principles Spring 2012 Dan C. Marinescu Office: HEC 304 Office hours: M-Wd 5:00-6:00 PM
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Lecture 6 - Monday January 30 n Reading assignment: the class notes “Distributed systems-basic concepts” and “Petri Nets” available online. n Last time n Middleware: ¨ Transparency (Access, Location, Concurrency, Replication, Failure, Performance, Scaling). n Motivating example  Molecular dynamics computations n Communication in distributed systems ¨ Abstractions: process, thread, communication channel ¨ The state of a process ¨ Events: internal, communication ¨ Process history ¨ Space time diagrams ¨ Global state Lecture 6 2/16/12 2
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Today ¨ Distributed systems n Process coordination ¨ Lost messages ¨ Time, timeouts, and message recovery ¨ Causality n Logical clocks n Message delivery rules ¨ FIFO delivery ¨ Causal delivery n Runs and cuts n Distributed snapshots Lecture 6 2/16/12 3
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Bsic concepts n Process  a program in execution n Thread  a light-weight process. A thread of execution is the smallest unit of processing that can be scheduled by an operating system. n The state of a process  the ensemble of information about the process we need to restart it after it has been suspended. n Event  The change of state of a process n Communication channel  provides the means for processes or threads to communicate with one another and coordinate their actions by exchanging messages. n Message  a structured unit of information, which can be interpreted only in a semantic context by the sender and the receiver. n Communication among processes is done only by means of send(m) and receive(m) communication events where m is a message. n State of a communication channel  given two processes pi and pk the state of the channel, C(i,k) , from pi to pk consists of messages sent by pi but not yet received by pk Lecture 6 4 2/16/12
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Communication in the real-life distributed systems n Messages can be ¨ Lost ¨ Duplicated ¨ Affected by errors n In practice ¨ A messages has a unique name  sequence number ¨ To confirm reception of a message the receiver sends an acknowledgment ¨ Each acknowledgment has a sequence number as well as the sequence number of the message it acknowledges/. ¨ The sender sets up a
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This note was uploaded on 02/15/2012 for the course COP 5611 taught by Professor Staff during the Spring '08 term at University of Central Florida.

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Lecture6 - COT 5611 Operating Systems Design Principles...

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