Nachos Assignment #1: Build a thread system Tom Anderson ...

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This has resulted in several brawls in the laundromat, and you havebeen called in by the owner to x the problem. Assume that onethread handles each customer station. Explain how the same washingmachine can be assigned to two dierent customers.(b) Modify the code to eliminate the problem.(c) Re-write the code to solve the synchronization problem using locksand condition variables instead of semaphores.4. Implement an \alarm clock" class. Threads call \Alarm::GoToSleepFor(inthowLong)" to go to sleep for a period of time. The alarm clock canbe implemented using the hardware Timer device (cf. timer.h). Whenthe timer interrupt goes o, the Timer interrupt handler checks to seeif any thread that had been asleep needs to wake upnow. There is norequirement that threads start running immediately after waking up justput them on the ready queue after they have waited for the approximatelythe right amount of time.5. You've been hired by the University to build a controller for the elevatorin Evans Hall, using semaphores or condition variables. The elevator isrepresented as a thread each student or faculty member is also representedby a thread. In addition to the elevator manager, you need toimplement the routines called by the arriving student/faculty: \Arriving-GoingFromTo(int atFloor, int toFloor)". This should wake up the elevator,tell it which oor the person is on, and wait until the elevator arrivesbefore telling it which oortogoto. Theelevator is amazingly fast, butit is not instantaneous { it takes only 100 ticks to go from one oor tothe next. You may nd it useful to use your solution for part 4 here. Forsimplicity, you can assume there's only one elevator, and that it holds anarbitrary number of people. Of course, you should give priority to thosethreads going to or departing from the fth oor :-).6. You've just been hired by Mother Nature to help her out with the chemicalreaction to form water, which she doesn't seem to be able to get rightdue to synchronization problems. The trick is to get two H atoms andone O atom all together at the same time. The atoms are threads. EachH atom invokes a procedure hReady when it's ready to react, and eachO atom invokes a procedure oReady when it's ready. For this problem,you are to write the code for hReady and oReady. The procedures mustdelay until there are at least two H atoms and one O atom present, andthen one of the procedures must call the procedure makeWater (whichjustprints out a debug message that water was made). After the makeWatercall, two instances of hReady and one instance of oReady should return.Write the code for hReady and oReady using either semaphores or locksand condition variables for synchronization. Your solution must avoidstarvation and busy-waiting.4
7. You have been hired by Caltrans to synchronize trac over a narrow lightdutybridge on a public highway. Trac may only cross the bridge in onedirection at a time, and if there are ever more than 3 vehicles on the bridgeat one time, it will collapse under their weight. In this system, each caris represented by one thread, which executes the procedure OneVehiclewhen it arrives at the bridge:OneVehicle(int direc){ArriveBridge(direc)CrossBridge(direc)ExitBridge(direc)}In the code above, direc is either 0 or 1 it gives the direction in which thevehicle will cross the bridge.(a) Write the procedures ArriveBridge and ExitBridge (the CrossBridgeprocedure should just print out a debug message), using locks andcondition variables. ArriveBridge must not return until it safe forthe car to cross the bridge in the given direction (it must guaranteethat there will be no head-on collisions or bridge collapses). Exit-Bridge is called to indicate that the caller has nished crossing thebridge ExitBridge should take steps to let additional cars cross thebridge. This is a lightly-travelled rural bridge, so you do not need toguarantee fairness or freedom from starvation.(b) In your solution, if a car arrives while trac is currently moving in itsdirection of travel across the bridge, but there is another car alreadywaiting to cross in the opposite direction, will the new arrival crossbefore the car waiting on the other side, after the car on the otherside, or is it impossible to say? Explain briey.8. Implement (non-preemptive) priority scheduling. Modify the thread schedulerto always return the highest priority thread. (You will need to createa new constructor for Thread to take another parameter { the prioritylevel of the thread leave the old constructor alone since we'll need it forbackward compatibility.) You may assume that there are a xed, smallnumber of priority levels { for this assignment, you'll only need two levels.Can changing the relative priorities of the producers and consumer threadshave any aect on the output? For instance, what happens with twoproducers and one consumer, when one of the producers is higher prioritythan the other? What if the two producers are at the same priority, butthe consumer is at high priority?5
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Nachos Assignment #1: Build a thread system Tom Anderson ...

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