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Mohamed G. Gouda                                        CS 356
Spring      2008                                        Homework 3 Solution
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1. (5 points)

process p

inp w                : integer
var na, nr, ns, i, j : integer          {init. 0}
    akn              : boolean          {init. false}

begin
    na + w > ns             -> send data(ns, nr) to q;
                               ns, akn := ns + 1, false
[]  rcv ack(j) from q       -> na := max(j, na)
[]  timeout na < ns ^ (#ch.p.q + #ch.q.p = 0) ^ ~akn 
                            -> send data(na, nr) to q;
                               akn := false
[]  rcv data(i, j) from q   -> if i < nr -> akn := true
                               [] i = nr -> {accept data(i,j)}
                                            nr, akn := nr+1, true
                               [] i > nr -> {discard data(i,j)} skip
                               fi; 
                               na := max(j, na)
[]  akn                     -> akn := false; send ack(nr) to q
[]  rcv error from q        -> skip                                
end
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2. (5 points)

process p[i : 0..x-1]
const lmax 
inp   N      : set {g | p[g] is a neighbor of p[i]}
      load   : 0..(lmax-1)
var   ld     : array [N] of 0..lmax,
      b      : 0..1,		  
      d      : 0..(lmax-1)
par   g      : N

begin
    rcv chk(b, d) from p[g] -> if b = 0  -> ld[g] := max
                               [] b = 1  -> ld[g] := d
                               fi;
                               send chk(1, load) to p[g]
[]  rcv error from p[g]     -> skip                                
[]  timeout (#ch.p[i].p[g] + #ch.p[g].p[i]=0)
		            -> ld[g] := lmax;
                               if i < g  -> send chk(0, load) to p[g]
                               [] i >= g -> skip
                               fi
end

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