exercise7.adb

with Ada.Text_IO, Ada.Integer_Text_IO, Ada.Numerics.Float_Random;
use  Ada.Text_IO, Ada.Integer_Text_IO, Ada.Numerics.Float_Random;

procedure exercise7 is

    Count_Failed    : exception;    -- Exception to be raised when counting fails
    Gen             : Generator;    -- Random number generator

    protected type Transaction_Manager (N : Positive) is
        entry Finished;
        function Commit return Boolean;
        procedure Signal_Abort;
    private
        Finished_Gate_Open  : Boolean := False;
        Aborted             : Boolean := False;
        Should_Commit       : Boolean := True;
    end Transaction_Manager;
    protected body Transaction_Manager is
        entry Finished when Finished_Gate_Open or Finished'Count = N is
        begin
            ------------------------------------------
            -- PART 3: Complete the exit protocol here
            ------------------------------------------
	    Should_commit := not Aborted;
	    if Finished'Count > 0 then
	      Finished_Gate_Open := true;
	    else
	      Finished_Gate_Open := false;
	    end if;
	    
	    if Finished'Count = 0 then
	      Aborted := false;
	    end if;
	    -------------------------------------------
        end Finished;

        procedure Signal_Abort is
        begin
            Aborted := True;
        end Signal_Abort;

        function Commit return Boolean is
        begin
            return Should_Commit;
        end Commit;
    end Transaction_Manager;

    function Unreliable_Slow_Add (x : Integer) return Integer is
    Error_Rate : Constant := 0.15;  -- (between 0 and 1)
 
    begin
        -------------------------------------------
        -- PART 1: Create the transaction work here
        -------------------------------------------
	
	if Random(Gen) < Error_Rate then 
	   raise Count_Failed;			-- raise = throw 
	else 
	   delay 4*Duration(Random(Gen));
	   return x+10;
	end if;   
	--------------------------------------------
    end Unreliable_Slow_Add;

    task type Transaction_Worker (Initial : Integer; Manager : access Transaction_Manager);
    task body Transaction_Worker is
        Num         : Integer   := Initial;
        Prev        : Integer   := Num;
        Round_Num   : Integer   := 0;
    begin
        Put_Line ("Worker" & Integer'Image(Initial) & " started");

        loop
            Put_Line ("Worker" & Integer'Image(Initial) & " started round" & Integer'Image(Round_Num));
            Round_Num := Round_Num + 1;
            ---------------------------------------
            -- PART 2: Do the transaction work here             
            ---------------------------------------
	    begin
		Prev := Num;		
		Num := Unreliable_Slow_Add(Num);
	    exception
		when Count_Failed => Manager.Signal_Abort;
	    end;
	    Manager.Finished;	
            ----------------------------------------
            if Manager.Commit = True then
                Put_Line ("  Worker" & Integer'Image(Initial) & " comitting" & Integer'Image(Num));
            else
                Put_Line ("  Worker" & Integer'Image(Initial) &
                             " reverting from" & Integer'Image(Num) &
                             " to" & Integer'Image(Prev));
                -------------------------------------------
                -- PART 2: Roll back to previous value here
                -------------------------------------------
		Num := Prev;
		-------------------------------------------
            end if;
            Prev := Num;
            delay 0.5;

        end loop;
    end Transaction_Worker;

    Manager : aliased Transaction_Manager (3);

    Worker_1 : Transaction_Worker (0, Manager'Access);
    Worker_2 : Transaction_Worker (1, Manager'Access);
    Worker_3 : Transaction_Worker (2, Manager'Access);

begin
    Reset(Gen); -- Seed the 

 --number generator
end exercise7;