UNIVERSITY OF MORATUWA

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1 UNIVERSITY OF MORATUWA FACULTY OF ENGINEERING DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING B.Sc. Egieerig 2010 Itake Semester 7 Examiatio CS4532 CONCURRENT PROGRAMMING Time allowed: 2 Hours September 2014 ADDITIONAL MATERIAL: Noe INSTRUCTIONS TO CANDIDATES: 1. This paper cosists of 5 questios i 7 pages. 2. Aswer ay 4 questios. 3. Start aswerig each of the mai questios o a ew page. 4. The maximum attaiable mark for each questio is give i brackets. 5. This examiatio accouts for 60% of the module assessmet. 6. This is a closed book examiatio. NB: It is a offece to be i possessio of uauthorised material durig the examiatio. 7. Oly calculators approved by the Faculty of Egieerig are permitted. 8. Assume reasoable values for ay data ot give i or with the examiatio paper. Clearly state such assumptios made o the script. 9. I case of ay doubt as to the iterpretatio of the wordig of a questio, make suitable assumptios ad clearly state them o the script. 10. This paper should be aswered oly i Eglish.

2 Questio 1 (25 marks) Explai three factors that cotributed to the migratio from uiprocessor systems to shared memory multiprocessor/multi-core systems? [6] Amdahl s law is used to fid the maximum expected improvemet to a overall system whe oly part of the system is improved. I the cotext of cocurret programmig, we ca preset it as follows: 1 p 1 p where p is the parallel fractio ad is the umber of processors. Suppose a computer program has a method M that caot be parallelized. M accouts for 20% of the program s executio time. The remaiig code is parallelized. a) How much speedup ca we gai, if we implemet the above program o a 8-core CPU? [2] b) Is it really worth ivestig a 8-core CPU to solve this problem? Briefly explai. [3] (iii) Suppose you belogs to a team of developers developig a ew programmig laguage that supports threads. The ew laguage also provides a prit() fuctio with the followig fuctio prototype: void prit(strig s); This fuctio is expected to sed the give strig s to the termial/cosole via Stadard Output Stream (stdout) buffer. I a typical system, stdout buffer is shared amog all threads ad processes i the system. Moreover, bulk atomic memory copyig is ot supported i typical systems. a) Provide four possible outcomes of the followig program writte usig the ew laguage. Clearly state ay assumptios. Thread oe{ prit("blue"); Thread two{ prit("red"); b) Provide a suitable pseudo code for the implemetatio of prit(). Make sure there are o race coditios. [6] c) Give the possibility that may threads may simultaeously call prit(), discuss about the efficiecy of your implemetatio i (b). [4] [4] Page 2 of 7

3 Questio 2 (25 marks) Compare ad cotrast (i.e., idetify the similarities ad dissimilarities) locks, semaphores, ad moitors. [6] Cosider the followig programs. Thread 1 prit Red + math.rad(10); Thread 2 prit Blue + math.rad(10); Math.rad(10) geerates a radom value betwee 1 ad 10. Chage the above program to make sure the sum of all Red values it had prited so far is always less tha the sum of all Blue values it has prited. For example, if Blue had prited 1, 5, ad 7 the it is OK for Red to prit 2 ad 9 because < Your implemetatio should be efficiet. [14] (iii) Followig implemetatio of Accout class is to be used to keep track of customers accouts i a bak. Discuss whether this implemetatio is free from deadlocks. class Accout { double balace; //accout balace it id; //accouts o void withdraw(double amout){ balace -= amout; void deposit(double amout){ balace += amout; // withdraw moey //deposit moey //Trasfer moey betwee accouts void trasfer(accout from, Accout to, double amout){ lock(from); lock(to); from.withdraw(amout); to.deposit(amout); release(to); release(from); [5] Page 3 of 7

4 Questio 3 (25 marks) A semaphore is a couter capable of providig mutual exclusio ad sychroizatio. Briefly explai the meaig of this statemet. [4] Cosider the followig program with 2 threads. Thread 1 prit Red ; Thread 2 prit Blue ; prit Blue ; a) Provide four possible outcomes of the above program. b) Rewrite the above program usig a semaphore(s) ad oly oe prit statemet per thread such that we get the followig sequece of outputs. Blue, Blue, Red, Blue, Blue, Red, Blue,. [9] (iii) The geometric mea is oe of the several kids of averages. It is ofte used whe comparig differet items where each item has multiple properties, e.g., while comparig the performace of two database servers. Geometric mea of real umbers x1, x2, x3,... x ca be calculated as follows: [2] i 1 x i 1/ x x x x Outlie a MPI program (usig pseudo code) that ca be used to calculate the geometric mea of oe millio real umbers. Oce the calculatio is complete, all process ivolved i the computatio eed to kow the value. Use relevat MPI fuctios that are give i the Appedix. Note that it is impractical to create oe millio cocurret processes/threads [10] Page 4 of 7

5 Questio 4 (25 marks) Usig a suitable diagram illustrate the process of fidig cocurrecy i a give problem. Briefly explai each step. [6] Explai how a Depedecy Graph helps to evaluate the desig of a cocurret solutio. [5] (iii) Cosider the followig SQL-like query. Query: MODEL = Hoda Civic AND YEAR = 2001 AND (COLOR = Gree OR COLOR = White ) Evaluate the Depedecy Graph of the above query usig criteria metioed i Questio. Your evaluatio should cosider the degree of cocurrecy ad critical path. [8] (iv) Static or dyamic load balacig is essetial i most systems to icrease the resource utilizatio ad quality of service. What type of load balacig would you recommed for the followig problems? Justify your recommedatio. (a) Matrix-Matrix multiplicatio. [3] (b) While crackig 10,000 password-protected word documets foud from a suspected terrorist s laptop. Assume brute-force approach is used to crack passwords. [3] Page 5 of 7

6 Questio 5 (25 marks) There are several techiques to covert a colour image to grayscale. The lightess techique averages the most promiet ad least promiet colours usig the followig equatio: max( R, G, B) mi( R, G, B) 2 where R, G, B refers to three fudametal colours of a pixel. A grayscale image is obtaied by applyig this equatio to each pixel separately. Outlie a CUDA program to covert a give colour image to grayscale usig the lightess techique. Your solutio should iclude the code for the Kerel fuctio ad the code required to ivocate the Kerel fuctio. Hit: a typical CUDA supported GPU ca oly hadle 1,024 threads per block. [13] Outlie a solutio to each of the followig problems. Explai how it will address the give problem while satisfyig safety ad liveess properties (formal proofs are ot required). (a) SETI is oe of the largest voluteer computig platforms that remotely executes jobs usig idle computig resources. These jobs iclude aalysig images/data from optical ad radio telescopes for the presece of extra-terrestrial life. Over 200,000 SETI voluteer odes are active at ay give time. Each ode cotacts the SETI server ad asks for a ew job based o its computig capabilities. The same job is submitted oly to two odes to icrease the reliability while maitaiig better resource utilizatio (voluteers odes may fail at ay time). Oce the job is completed, ode submits the aswer ad asks for aother job. You are required to desig a cocurret job dispatchig solutio that allocates oly two copies of the same job to voluteer odes. [6] (b) Clusterig is a fudametal approach to maage Mobile Ad-hoc Networks (MANETs). I clustered etworks, odes are classified as cluster members ad cluster heads. A cluster member is a ordiary ode which seds its request to its cluster head. A cluster head is resposible for maagig the cluster, hadlig itracluster requests, ad participatig i iter-cluster operatios. While all odes may be willig to become a cluster head, oly oe of the odes i a give eighbour should be selected as a cluster head. You are required to desig a cluster head selectio solutio for a give eighbourhood. [6] Page 6 of 7

7 Appedix MPI Fuctios it MPI_Iit(it *argc, char **argv) it MPI_Comm_size(MPI_Comm comm, it *size) it MPI_Comm_rak(MPI_Comm comm, it *rak) it MPI_Fialize() it MPI_Sed (void *buf,it cout, MPI_Datatype datatype, it dest, it tag, MPI_Comm comm) it MPI_Recv (void *buf,it cout, MPI_Datatype datatype, it source, it tag, MPI_Comm comm, MPI_Status *status) it MPI_Reduce(void *sedbuf, void *recvbuf, it cout, MPI_Datatype datatype, MPI_Op op, it root, MPI_Comm comm) it MPI_Allgather(void *sedbuf, it sedcout, MPI_Datatype sedtype, void *recvbuf, it recvcout, MPI_Datatype recvtype, MPI_Comm comm) it MPI_Allreduce (void *sedbuf, void *recvbuf, it cout, MPI_Datatype datatype, MPI_Op op, MPI_Comm comm) it MPI_Bcast( void *buffer, it cout, MPI_Datatype datatype, it root, MPI_Comm comm) it MPI_Gather(void *sedbuf, it sedct, MPI_Datatype sedtype, void *recvbuf, it recvct, MPI_Datatype recvtype, it root, MPI_Comm comm) it MPI_Scatter(void *sedbuf, it sedct, MPI_Datatype sedtype, void *recvbuf, it recvct, MPI_Datatype recvtype, it root, MPI_Comm comm) END OF THE PAPER Page 7 of 7