Computer Science 5204 Operating Systems Fall, 2012 Dr. Dennis Kafura Course Overview 1

CS 5204 – Operating Systems2 Organization Material intensive  35 +/- papers  25 audio/video files  No required text Balance  Theory vs. technology  Contemporary vs. classic  Survey vs. depth  Centralized vs. distributed Syllabus on web site

Course Overview CS 5204 – Operating Systems3 Course Web site

Course Overview Piazza An online question-answer/discussion system Register  Go to  Search for “CS 5204”  Create an account using your VT address Dennis Kafura – CS5204 – Operating Systems4 Help:

Course Overview Meeting Schedule Tuesday, September 4 (next week)  We will NOT meet  This will be a “virtual class” – see web site for complete materials (papers, lectures, problem set, …) Tuesday, September 11  We will have the scheduled VTEL meeting  We can decide to meet via VTEL Option 1: every week Option 2: every other week (alternating “real” and “virtual” classes) Dennis Kafura – CS5204 – Operating Systems5

Course Overview Intangibles Confidence that you can read and master material in the published OS literature Practice in your ability to present complex technical material to a knowledgeable audience Some appreciation for the history and evolution of ideas and technology Dennis Kafura – CS5204 – Operating Systems6

Course Overview CS 5204 – Operating Systems7 Major Topics and Themes Topic Theme AtomicityOrderConsistencyTheoryProtocols Google /Cloud 1. Concurrency xxxx 2. Security xx 3. Storage xxxx 4. Fault tolerance xxxxx

Course Overview CS 5204 – Operating Systems8 1. Concurrency What are the problems and issues in developing systems with concurrent activities? What are emerging models for concurrent programming? How can the problems with multi-threaded programming be alleviated? How can transaction-style semantics be supported locally in hardware or software? How can concurrency and communication be represented formally?

Course Overview CS 5204 – Operating Systems9 Process vs. Thread Models... user kernel... user kernel process-centered thread-centered

Course Overview Models of Concurrent Computation CS 5204 – Operating Systems10 MapReduce

Course Overview CS 5204 – Operating Systems11 Thread-per-process models Sequential process Communication channel Communicating Sequential Processes Sammati Grace

Course Overview CS 5204 – Operating Systems12 Supporting Transaction Semantics repeat { BeginTransaction(); /* initialize transaction */ success = Validate(); /* test if inputs consistent */ if (success) { success = Commit(); /* attempt permanent update */ if (!success) Abort();/* terminate if unable to commit */ } EndTransaction(); /* close transaction */ } until (success); TM Object Transaction New Object Old Object Locator Transaction object data

Course Overview CS 5204 – Operating Systems13 π-Calculus An algebra that captures the notions of communication, interaction, and synchronization among concurrently executing entities. Control Trans Idtrans talk 1 lose 1 switch 1 lose 2 gain 2 gain 1 Control IdTrans Trans talk 2 lose 1 switch 2 lose 2 gain 2 gain 1

Course Overview CS 5204 – Operating Systems14 2. Security How can rights for access control be structured for effective use and management? How can a digital document be “signed” so as to identify authorship? How can communicating parties be confident of each other’s identities? How can a group of individuals share a secret? How can identities serve as cryptographic keys? How can access policies be expressed and reasoned about?

Course Overview CS 5204 – Operating Systems15 Security Overview Models of Protection Cryptographic Security Adelman, Rivest, Shamir

Course Overview Security Overview Dennis Kafura – CS5204 – Operating Systems16 Information Flow Modeling classes of information Determining flows among the classes of information Enforcing constraints on the flow of information among system components

Course Overview CS 5204 – Operating Systems17 Security in distributed systems Describe explicit trust relationships Express security token issuance policies Provide security tokens that contain identities, capabilities, and/or delegation policies Express resource authorization and delegation policies

Course Overview CS 5204 – Operating Systems18 3. Storage How can scalable, large-scale storage systems be constructed? How can large-scale storage systems deal with issues of reliability and performance? How can peer-to-peer systems be structured to provide a usable storage system? How can “database”-like (more structured) storage be provided for tera-bytes of data?

Course Overview CS 5204 – Operating Systems19 Storage Storage system (Dynamo) in Amazon’s service- oriented architecture Peer-to-peer file system

Course Overview CS 5204 – Operating Systems20 Storage Google File System Structured storage

Course Overview CS 5204 – Operating Systems21 4. Fault Tolerance How can events be ordered in a distributed system lacking a shared clock? How can this ordering give rise to a form of virtual time? What are basic approaches to recovery from failure? What is the taxonomy of strategies of “backward” recovery? How can the state of system be captured so that it can be recovered in the event of failure? How can distributed elements agree on commit to accepting a change in the system state?

Course Overview CS 5204 – Operating Systems22 Event Ordering How can the events on P be related to the events on Q? Which events of P “happened before” which events of Q? When does it matter how we answer these questions? Q P P1P1 Q1Q1 P3P3 P2P2 Q3Q3 Q2Q2

Course Overview CS 5204 – Operating Systems23 Recovery erroneous state error valid state failure causes fault leads to recovery An error is a manifestation of a fault that can lead to a failure. Failure Recovery: backward recovery operation­based (do­undo­redo logs) state­based (checkpoints) forward recovery