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Mohamed G. Gouda                                        CS 356
Summer 2006                                             Homework 3 
Solution
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1. 

process p[i:0..n-1]
inp     N: set{g|p[g] is a neighbor of p[i]}
var     up: array[N] of boolean,
        ready: array[N] of boolean {init true}
par     g: N

begin

     ready[g] -> ready[g]; = false;
                 send chkrqst  to p[g]

[]   rcv chkrply from p[g] -> up[g], ready[g] := true,true

[]   rcv chkrqst from p[g] -> send chkrply to p[g]

[]   timeout  ~ready[g].p[i] ^ (#ch.p[i].p[g] + #ch.p[g].p[i] = 0)
              ->up[g], ready[g] := false,true

end

2.

process p[i:0..n-1]
inp     N: set{g|p[g] is a neighbor of p[i]}
var     up: array[N] of boolean,
        b: 0..1,
        x,y,sum: integer
	isum: array[N] of integer

begin

     rcv chk(b,x,y,sum) from p[g] -> 
         if b=0 v sum != isum[g] -> up[g] :=false
         [] b=1 ^ sum  = isum[g] -> up[g] :=true
         fi;
         sum := x+y;
         x, y := any,any;
         isum[g] := x+y;
         send chk(1,x,y,sum) to p[g]

[]   rcv error from p[g] -> skip

[]   timeout (#ch.p[i].p[g] + #ch.p[g].p[i] = 0)
	      ->
              up[g]]:= false;
              if i<g -> x,y := any,any; isum[g] := x+y;
                        send chk(0,x,y,sum) to p[g]
              [] i>= -> skip
              fi

end

3.

process p[0]
const n
inp up: array[1..n-1] of boolean
var ts : integer,     {init. 0}
    m  : 1..n,

begin

     true -> ts, m := ts+1,1;
             do m<n ->
                if up[m] -> send st(up,ts) to p[m];
                []~up[m] -> skip
                fi; m := m+1
             od

end

process p[i:1..n-1]
var vp,v: array [1..n-1] of boolean,
    ts,t: integer     {initially ts=0}

begin

     rcv st( v,t) from p[0] ->
         if t<= ts -> skip
         [] t>ts   -> ts,vp := t,v
         fi

end