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Mohamed G. Gouda                                        CS 356
Spring      2008                                        Homework 2 Solution
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1. (5 points)

process q
var rcvd : array [integer] of integer
    d    : integer,                     {rcvd data}
    x    : integer,                     {points to where to store next
                                         first data init. 0}
    y    : integer,                     {points to where to store next
                                         second data init. 1}
    z    : integer,                     {points to where to store next
                                         third data init. 2} 
begin
     rcv first(d) from p    -> rcvd[x], x := d, x+3
[]   rcv second(d) from p   -> rcvd[y], y := d, y+3
[]   rcv third(d) from p    -> rcvd[z], z := d, z+3
end
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2. (5 points)

process p[i : 0..x-1]
const y
inp   m      : integer
var   conp   : boolean,           {init. false}
      cansnd : 0..m,		  
      peer   : 0..y-1

begin
    timeout ~conp ^ (for all j: 0<=j<n: #ch.p[i].q[j]+#ch.q[j].p[i]=0)
		  -> peer := any; send crqst to q[peer] 
[]  rcv crply from q[peer] -> conp, cansnd := true, m
[]  conp -> if cansnd > 0  -> send data to q[peer];
                              cansnd := cansnd - 1
            [] true        -> send drqst to q[peer];
                              cansnd := 0
            fi
[]  rcv drply from q[peer] -> conp := false                                     
end


process q[j : 0..y-1]
const x
var   conq   : boolean,            {init. false}
      peer   : 0..x-1
par   i      : 0..x-1

begin
      rcv crqst from p[i]    -> 
                         if true            -> conq := false; 
					       send drply to p[i]
                         [] ~conq v peer=i  -> conq, peer := true, i;
                                               send crply to p[i]
                         fi
[]    conq                   -> conq := false
[]    rcv data from p[i]     ->
                         if conq ^ peer =  i -> {accept data} skip
                         []~conq v peer != i -> {discard data}
                                                send drply to p[i]
                         fi
[]    rcv drqst from p[i]    ->
                         if peer != i        -> skip
                         [] peer  = i        -> conq := false
                         fi;
                         send drply to p[i]                                    
end
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