Systems Simulation & Modeling
Systems Simulation & Modeling CS 6910
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This 5 page Class Notes was uploaded by Lisette Hodkiewicz on Wednesday September 30, 2015. The Class Notes belongs to CS 6910 at Western Michigan University taught by Staff in Fall. Since its upload, it has received 10 views. For similar materials see /class/216890/cs-6910-western-michigan-university in ComputerScienence at Western Michigan University.
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Date Created: 09/30/15
9222008 I Overview C56910 TestingVerification I How to analyze propertis ofa model of Concurrent Programs Today Explicit state model checking I Reachability Analysis I In between certain graph traversal Explicit State Reachability Analysis algorimms Reachability in FiniteState Si Model Checking I Machines I So far we have seen ways to specify 39 eaChabllltY analYSlS the propertis Central In model checking 731 I Model checking addresses ef cient 39 safer 3 emes algorithms to decide whether the 39 bgalf egcieet josftg it gs fell slstem sat39s es mel lwe39ty39 the initial states 4 I First approach Explicit state model Usually interested in r ckIng rachability of unsafe or lt bad states Algorithm Reachability in Algorithm Reachability in g FSMs I FSMs 39 mesa A M 5 Mums wiiiiii Qumlr39 s ii iii 33 553 4 n a we nuiii Qua mm 1 mini um xIHIDERdn rurnnlmlERdn te wdlhen insBaLIllmn 3949me I mainr mu 395mum m amti and ir a it C mgnmiium lrwnmum 1 add i ii uid m 0 Mi a X in gum midi Au aim ml39l i a 1 rm m in mdw In aid w 39 e I M I mxl 539slm in miquot WSW 395 M 9222008 Algorithm Reachability in I FSMs maul a w Qumn 0 ch mm a rm Queue for u w an do in But um ulz Sy5 zm a mum an n il l a Each m and x in mm mid l m Qnmc if m fur md whdu 351 5339 un ls nh Algorithm Reachability in I FSMs ad whil mK39 ysmm 5 saw canou mum and whil uwsm 39s are Algorithm Reachability in FSMs mm as 1 mun3 musym mushquot mi ir Ir p g mwi Hum 66 l w Rand mm 1 m um a 1r d or and whlla dwii swml in uh Algorithm Reachability in FSMs wuu a 9222008 Forward Reachability Hopertles can be analyzed by enumerating all reachable states from the initial state enough to check safety For safety properties it is each reached state for its g Backward Reachability Prupertles tan alm be analyzed by ennrneratlng all states that tan reatn tne unsafe state Iteratlverley tanpnte tne Dredetessms of states that can end up n an unsa state Fm sarety tnetk tnat none of tnese states l5 an rnrtral state sanetrnes could he raster tnan forward reatnatrlrzy less states to enum erate Review Depth First Search vs I Breadth First Search Graph Traversal algorithms DepthFirst Search DFS Use stack LIFO to keep states matneeg further I LlF LaSt39ll i rstrout Searches state space by followlrlg sngle path at a ume BreadthFirst Search BFS Use Hroegnene to keep states that need further processng I FIFO FlfSt ll i rstrout he te earc ssta space by processlrlg rounds of forward steps Rev w Potential DFS Traversal lltxnn at some initial sum L at cl 391 aBlpic All A I n r 1d Ll I39nillel cL a Haunt mlnn child 39 c tsnranctbtcknackl 39 u r klmnkp D E 39 a c plckutlld slum VIKV V I v F yICL n c l luld rk nontlnmtbnmmckl ll ReVIew Potential BFS Traversal lrm momennnnltme uusc clnldmn mm qncnc 1m Remoye 139 mid nll ns unseen cluldx en inm queue r Rsmow D2uldu1uslmseen clnltlxen nno nnene 121quot RemmeE mltlauns seeucluldlen r to t ucl Remove t on all us unseen cimmen to qnene a l Dmtt El Counterexamples wnen properues are ylolateg model checker can ovl ug trace from the state explorauon pr de a p Very useful to analyze one proplernauc behavlor ul acmal rublemlns stem d e tn lrlmrre nvlm rn rrnes u tt nrnent rmdellrlg Counterexample ls used to locallze the fault and x lt Generally speakll lg counterexample are the rnost useful feature of model checkers for actual deslgnersusers Many tonntereyarnples dlsmvered early rn deslgrl stage O en more useful than f lnal proved answa 9222008 Computing Counterexamples Reachabiiity aigonmm impiementauons DFS or BFS DFS Anepmnrst Search ND ad morin informauw needs in be stored in compute Duntarexampie Memorye iment BFS SreadmrFirst Search Finds a wonst Duntarexampie Requires additionai information m comma Duntarexampie Needs in 51am for each rahabie 5mg mm m predecessor i5 Computing Counterexamples ll usmg DFS Computing Counterexamples I using DFS IrVianiidi s n 5 M a mm 1 millmm e a t 5 Hindu m m m a may 2 iwmwu ma rm M m a my msim u m Computing Counterexamples usmg DFS Hum a 0mm u mm m whlln nm 2 s 1 M u z m nu w Mbnkk an i m m 4a uvimmmme an a mi quot m w k mm mmm mammal Mn 94 u i mm mm quot4 n m u 1 pm 1 Mn u mama s x m i u u IHIn u mum Computing Counterexamples hum min wnu um s i m 4 k six am an a 7 Im wh u ah i m mm Ju Irviwimkm a u m mm m ma mmum e n rdli39imuli mm a a m a s M y a m mum in ummhmmwm Mummy n 6 m u mm quot5a um i 1 ma n i m m u minim quot1 Minn quotHumn m mm svmlmlkl unlit mu mm um 9222008 Case Study NASA s PathFinder on Mars 1997 Computing Counterexamples using DFS Fixmmnudt mtme quotmagiMme mu M n Milt ul ddfllmhn IMMIER datum uni rumbar Ine mlhm I m M39Sy m a mum all If lllll ml vul ud Huh aid39Smu 39 nh39l Modeling NASA s Path nder Problem Case Study NASA s PathFinder on Mars 1997 Design fault caused rover to loose contact with earth Priority inversion problem caused intermittent deadlock Global realtime operating system would discover malfunction and initiate system reset Bug was traced through logging mechanism and xed with software update from earth Problem description presented here highly Simpil ie Based on Holzmann The Spin Model Checkerquot chapter 5 1499 lighsmmsldlm mm H mutex miilexhusy Modeling NASA s Path nder Problem wuiu vnd rm way Wlfrea iluhsmodillzd nulex1lvee Ia slatzldleA C lbquot miliexdveta w W Mum a mligninu quotmum Imuihi 39 s is Wailing while law an uiiorliy lock A um i Ilwhillurlwd whnu in He Banditk reached n 5mm morin proces priorin process was running but cannolcolnrrlele due 0 hi
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