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Parallel Programming WS 2014/2015 - Solution 4

Kastens, Pfahler
Institut für Informatik, Fakultät für Elektrotechnik, Informatik und Mathematik, Universität Paderborn
Dec 08, 2014

Solution for Exercise 1

a)
The monitor invariant: 
   // to be enforced by waiting
   seats >= seated >= transported

// guaranteed by execution order
   seats >=  transported
b)
The necessary waiting conditions and counter increments:

Entry Procedure wait while ... Modify counters
ride 
seats <= seated
 

seated++;
 
offer 
 
 

seats += 8;
 

seated < transported + 8;
 

transported += 8;
 
c)
To substitute the increasing counters by limited counters, we define two new counters: 
   freeseats = seats - seated
   entered = seated - transported
The counter actions and waiting conditions are transformed to:

Entry Procedure wait while ... Modify counters
ride 
freeseats <= 0
 

freeseats--;
entered++;
offer 
 
 

freeseats = 8;
 

entered < 8;
 

entered = 0;
 
d)
LAB: A Java monitor that can be used with the FAShuttle simulation is provided in directory blatt4/FAShuttle.sol.

Solution for Exercise 2

Directory blatt4/dices.sol contains an implementation of the complete dice simulation.

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