Tentamen vid Institutionen för Datavetenskap, Linköpings universitet. TDDD36 Säkra mobila System (Systemprogramvara)

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1 TENTAMEN TDDD36 Säkra mobila System (Systemprogramvara) Datum: Tid: 8-12 Lokal: TER3 Jourhavande-lärare: Massimiliano Raciti (jour runda, telefon: ) Simin Nadjm-Tehrani (endast via telefon ) Hjälpmedel: Poängantal: Miniräknare, Lexikon 40p Betyg: 3, 4 and 5: U: - 19 p 3: p 4: p 5: p INSTRUCTIONS: Write your anonymous ID number on each sheet of paper that you hand in. Further, pages should only contain one answer per page (answers to sub-questions can be on the same page). You are asked to only answer on the front page of the paper. Sort all the sheets that you hand in with respect to the number of the question. Your answers can be presented in Swedish or English, but the questions that are in English can be corrected by a non-swedish teacher. Make sure your answers include motivations and are presented precisely. A correct answer without any motivation will not be given any credits. Incorrect answers embedded in a partially correct one reduce the points given for that answer. Points will not be given to answers that cannot be read due to bad handwriting. Hints: Try to dispose of your time on each question in proportion of the assignment points. In those cases where you are in doubt about the question, write down your interpretation and your assumptions, and answer the question based on the interpretation. Figures can be of help when describing but should be accompanied by a text description. Results are reported no later than November 14, Good luck! Simin Nadjm-Tehrani Examiner TDDD36, Systems Software

2 Q1: a) For the wedding of Princess Victoria of Sweden three desserts were ordered and three bakers were selected to prepare each of them. In order to prepare the cakes some tools were available: two ovens, two mixers, two fridges, and three baking pans. Nevertheless some of them belonged to (were owned by) some of the bakers, who were not willing to share them (i.e. release them) until they prepared their own cake. Baker A owned one oven, one fridge, and one baking pan. Baker B owned one mixer, and baker C owned two baking pans. Assume the cakes must be prepared sequentially, i.e. one baker cannot start the process while another cake is under preparation. If each baker requires up to one oven, one mixer, one fridge, and two baking pans to prepare a cake, we would like to know: can the all the cakes be prepared? Relate this problem to the Banker's algorithm for multiple resource allocation in computer systems, and use the concepts from that algorithm to show whether a sequence of cake completions is possible. (6 poäng) b) Att åstadkomma ömsesidig uteslutning med hjälp av semaforer innebär att man måste kunna implementera wait- och signal-operationerna på semaforn på ett atomiskt sätt (en. atomic ). Förklara vad atomicitet betyder i detta sammanhang, och ange två metoder som kan användas för att garantera atomicitet för dessa operationer. (3 poäng) c) In Stockholm Tivoli there is a roller coaster called Jetline. It has a track with loops and curves with many cars where people take rides at fast speed. Along the track there are three cameras. Each camera takes pictures of the people when a car passes in front of it. The system is controlled by a single processor which runs the six processes, three devoted to capture the pictures, Ci (i: 1..3) and three devoted to process and store the pictures, Pi (i: 1..3). Since the pictures are stored in a shared database, mutual exclusion to access the database must be guaranteed. Implement an algorithm using the database encapsulated in a monitor. In order to decouple the rate of capturing pictures and processing them, three buffers Bi (i: 1..3) are shared pair-wise (Each Bi shared by the pair Ci and Pi). You should describe your algorithm by writing the pseudo-code for all the processes, but are not expected to produce the details of the pseudo-code for operations on the buffers or the storage in database. (6 poäng) e) Betrakta följande två processer som ska köras på samma processor och anta att tilldelning operationen är inte atomiskt implementerat i maskinspråk. Identifiera den kritiska sektionen i varje process. Du kan t.ex. skriva av koden och rita en cirkel kring delar av koden som ska betraktas som kritisk sektion. Motivera ditt val! Process A Process B while true do while true do {X = X+1; { Z = 1 Sq = X^2; if Sq > Limit then display(sq) } W = Z-1 display(w) } (5 poäng)

3 Q2: a) Take a stand on the following propositions (true or false) and motivate your answer! 1) Stock exchange applications have jitter parameters among QoS requirements. 2) Voice over IP is an elastic application in the QoS terminology. b) Consider a document sharing application where different users in a group can cooperate by reading and writing to a set of common documents. Decide which of the following properties is a functional property and which is an extra-functional property (also sometimes called a non-functional property), and motivate your answer! Q3: 1) The system shall keep a log of all changes done by each user for each of the documents. 2) No documents uploaded to a central repository are lost. 3) Documents that are larger than 30Mb are not accepted for common storage. 4) A document can be retrieved from the central repository within 20 seconds from sending a request. a) Vad kännetecknar den asynkrona modellen för distribuerade system? (2 poäng) b) What is meant by interoperability and scalability in the context of architectural solutions in distributed systems? Q4: a) Memory leaks and unreleased file locks are two examples of phenomena that are collectively referred to as software aging. Relate these two to the notions of faults, error and failure. (2 poäng) b) Compare the notions of fault prevention and fault tolerance and provide one example technique to achieve each of them.

4 Glossary: English to Swedish atomic atomisk (oavbrytbar) request begäran availability tillgänglighet response time responstid avoid undvika safety säkerhet bandwidth bandbredd scheduler schemaläggare broker medlare security säkerhet clock drift klockdrift serialisable - serialiserbar concurrency samtidighet shaping - formning consistency konsistens shared memory gemensamt minne deadlock låsning (baklås) starvation svält delay fördröjning sufficient condition- tillräckligt villkor deliberate avsiktlig synchronisation synkronisering dependability pålitlighet system call systemanrop diversity mångfald thread - tråd error felyttring throughput genomströmning event händelse trace spår failure haveri transparency transparens fault felkälla trust tillit fault tolerance feltolerans validation validering forecast förutse verification - verifiering inheritance arv vulnerability - sårbarhet integrity dataintegritet interleavings sammanflätningar interoperability interoperabilitet intrusion intrång latency - latens maintainability reparerbarhet malicious - illvillig middleware - mellanvara mutual exclusion ömsesidig uteslutning necessary condition nödvändigt villkor non-functional property ickefunktionell egenskap omission utelämnande performance prestanda preemptible avbrytbar prevent förebygga quality of service tjänstekvalitet race condition kapplöpningstillstånd release - släppning reliability tillförlitlighet rendundancy redundans replica kopia replication replikering

5 Swedish English arv - inheritance atomisk (oavbrytbar) atomic avbrytbar - preemptible avsiktlig - deliberate bandbredd - bandwidth begäran - request dataintegritet - integrity felkälla - fault feltolerans - fault tolerance felyttring - error fördröjning - delay förebygga - prevent formning - shaping förutse - forecast gemensamt minne - shared memory genomströmning - throughput händelse - event haveri - failure ickefunktionell egenskap - non-functional property illvillig - malicious interoperabilitet - interoperability intrång intrusion kapplöpningstillstånd race condition klockdrift - clock drift konsistens - consistency kopia - replica låsning (baklås) - deadlock latens - latency mångfald - diversity medlare - broker mellanvara - middleware nödvändigt villkor - necessary condition ömsesidig uteslutning - mutual exclusion pålitlighet - dependability prestanda - performance redundans - rendundancy reparerbarhet - maintainability replikering - replication responstid - response time säkerhet - safety säkerhet - security sammanflätningar - interleavings samtidighet - concurrency sårbarhet - vulnerability schemaläggare - scheduler serialiserbar - serialisable släppning release spår - trace svält - starvation synkronisering - synchronisation systemanrop - system call tillförlitlighet - reliability tillgänglighet - availability tillit - trust tillräckligt villkor - sufficient condition tjänstekvalitet - quality of service tråd - thread transparens - transparency undvika - avoid utelämnande - omission validering - validation verifiering - verification