package rw21 is

procedure readWork;

procedure writeWork;

task Reader_1 is
end Reader_1;

task Reader_2 is
end Reader_2;

task Writer_1 is
end Writer_1;

task Read_Write_Control is
  entry Start_Read;
  entry Stop_Read;
  entry Start_Write;
  entry Stop_Write;
end Read_Write_Control;

end rw21;

package body rw21 is

procedure readWork is
begin
	delay 1.0;
end readWork;

procedure writeWork is
begin
	delay 1.0;
end writeWork;


task body Reader_1 is
begin		-- Reader_1
   loop
      Read_Write_Control.Start_Read;	
      readWork;
      Read_Write_Control.Stop_Read;
   end loop;
end Reader_1;

task body Reader_2 is
begin		-- Reader_2
   loop
      Read_Write_Control.Start_Rea
      readWork;
      Read_Write_Control.Stop_Read;
   end loop;
end Reader_2;


task body Writer_1 is
begin
   loop
      Read_Write_Control.Start_Write;	
      writeWork;
      Read_Write_Control.Stop_Write;
   end loop;
end Writer_1;

task body Read_Write_Control is
   ActiveReaders  : Natural range 0..2;
   WriterPresent  : BOOLEAN := FALSE;
   ErrorFlag      : BOOLEAN := FALSE;
begin
   -- force a write first
   accept Start_Write;
   accept Stop_Write;

   loop
      select when not WriterPresent => accept Start_Read;
         ActiveReaders := ActiveReaders+1;

      or accept Stop_Read;
         if WriterPresent and (ActiveReaders = 1 or ActiveReaders = 2) then
            ErrorFlag := TRUE;
         end if;

         ActiveReaders := ActiveReaders-1;

      or when ActiveReaders = 0 and not WriterPresent => accept Start_Write;
         WriterPresent := TRUE;

      or accept Stop_Write;
         if WriterPresent and (ActiveReaders = 1 or ActiveReaders = 2) then
            ErrorFlag := True;
         end if;

         WriterPresent := FALSE;

      end select;
   end loop;
end Read_Write_Control;

end rw21;