Parallel Programming WS 2014/2015 - Assignment 7

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

Feb. 02, 2015

Exercise 1 (Synchronous Message Passing)

Consider the following CSP program:

   process Compare
      var i : integer;
          x : (1..10)integer;
      i := 1;
      do i <= 10 -> if x(i) >= 0 -> skip;
                    [] x(i) < 0  -> Count!x(i);
                    fi
                    i := i + 1;
      od
   end
   
   process Count
      var y, sum : integer;
      sum := 0;
      do Compare?y -> sum := sum + y;
      od;
      Print!sum
   end

What does this program compute? How does it terminate?

Exercise 2 (Synchronous Message Passing)

Write a system of processes "Even", "Odd", and "Sum" in the above notation.

"Even" sends the integer numbers 2, 4, .. 100 to process "Sum"
"Odd" sends the integer numbers 1, 3 .. 99 to process "Sum"
"Sum" adds all incoming numbers and sends the final result to standard process "Print".

Exercise 3 (Distributed Systems: Probe and echo)

Directory blatt7/ProbeNet contains a framework for probe and echo operations in a net (see Slide 73, Slide 74). Apply the probe and echo approach to compute the sum of numbers where one number is stored locally at each node of a net.

The framework consists of the following important classes:

Node.java: a node of the net with associated input port (channel); stores one operand of the sum
Message.java: represents the three kinds of messages needed (probes, dummies, echoes)
Main.java: builds an example net, creates and starts a Prober thread for each node

Complete the run() method of the inner class Main.Prober according to the algorithm outlined on Slide 74. The code for the initiator node is provided. Test your implementation using different initiators.

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