-- locks.adb
--           a simple use of protected type defining a lock
--           a lock protects a specific resource from concurrent use

with Ada.Text_IO;
procedure locks is -- just a demonstration

  protected type Resource is      -- this would typically be
    entry Seize;                  -- in a package and be "withed"
    procedure Release;            -- only one is needed other than
  private                         -- your choice of names
    Busy : Boolean := false;
  end Resource;

  protected body Resource is
    entry Seize when not Busy is
    begin
      Busy := true;  -- our only job here is to set the lock
    end Seize;
    procedure Release is
    begin
      Busy := false; -- just a procedure to unset the lock
    end Release;
  end Resource;

  --                Each lock is for an individual resource,
  --                use as many as you need.
  Lock1 : Resource;
  Lock2 : Resource;
  IO_Channel_7 : Resource;
  FIFO_Input_Buffer : Resource;
  Mutex : Resource;

begin
  Ada.Text_IO.Put_Line("locks running");

  Lock1.Seize;   -- These would normally be in tasks or
  Lock2.Seize;   -- other protected structures
  Lock2.Release;
  IO_Channel_7.Seize;
  Mutex.Release;

  Ada.Text_IO.Put_Line("locks finished");
end Locks;