View source for Yurttas/PL/IL/Ada-95/F/06/r-w/readers writers 00.adb

<syntaxhighlight lang="ada" line start="1" enclose="div">--
-- Copyright(C) 1998
-- All Rights Reserved. Salih Yurttas, ZCubes, BitsOfCode Software Systems, Inc..
--
-- Permission to use, copy, modify, and distribute this
-- software and its documentation for EDUCATIONAL purposes
-- and without fee is hereby granted provided that this
-- copyright notice appears in all copies.
--
 
-- date   : January 1, 1998.
-- author : Salih Yurttas.

-- readers_writers_00.adb


procedure Readers_Writers_00 is

  task type R_W_Scheduler is
    entry Start_Read;
    entry Stop_Read;
    entry Start_Write;
    entry Stop_Write;
  end R_W_Scheduler;

  task body R_W_Scheduler is
    Number_of_Readers : Integer := 0;
  begin
    loop
      select 
        when Start_Write'Count=0 =>
          accept Start_Read do
            Number_of_Readers := Number_of_Readers+1;
          end Start_Read;
        or accept Stop_Read do
             Number_of_Readers := Number_of_Readers-1;
           end Stop_Read;
        or when Number_of_Readers=0 =>
             accept Start_Write;
             accept Stop_Write;
             for I in 1..Start_Read'Count
             loop
               accept Start_Read do
                 Number_of_Readers := Number_of_Readers+1;
               end Start_Read;
             end loop;
      end select;
    end loop;
  end R_W_Scheduler;

begin

  null;

end Readers_Writers_00;
</syntaxhighlight>