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Mohamed G. Gouda                                        CS 356
Summer      2005                                        Homework 1 Solution
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1. 
Process q is the same as the one in the textbook.
Process p can be defined as follows: 

process p
var ready  : boolean   {true, initially}
    rcvrqst: boolean   {false,initially}

begin
   ready           -> send rqst to q;
                      ready := false

[] rcv rply from q -> if  rcvrqst -> send rply to q;
                                     rcvrqst:=false  
                      [] ~rcvrqst -> skip
                      fi; ready := true

[] rcv rqst from q -> if  ready -> send rply to q
                      [] ~ready -> rcvrqst:= true
                      fi;
end

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3. 
Process p can be defined as follows: 

process p
inp pr     : boolean   {pr.p = ~pr.q}
var ready  : boolean   {true, initially}
    rcvrqst: boolean   {false,initially}

begin
   ready           -> send rqst to q;
                      ready := false

[] rcv rply from q -> if  rcvrqst -> send rply to q;
                                     rcvrqst:=false  
                      [] ~rcvrqst -> skip
                      fi; ready := true

[] rcv rqst from q -> if  ready V ~pr -> send rply to q
                      [] ~ready ^  pr -> rcvrqst:= true
                      fi;
end