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------------------------------------------------------------------------------

--                                                                          --

--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --

--                                                                          --

--      S Y S T E M . T A S K I N G . P R O T E C T E D _ O B J E C T S     --

--                                                                          --

--                                  B o d y                                 --

--                                                                          --

--             Copyright (C) 1991-1994, Florida State University            --

--                     Copyright (C) 1995-2008, AdaCore                     --

--                                                                          --

-- GNARL is free software; you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion. GNARL is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNARL; see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNARL was developed by the GNARL team at Florida State University.       --

-- Extensive contributions were provided by Ada Core Technologies, Inc.     --

--                                                                          --

------------------------------------------------------------------------------

pragma Polling (Off);

--  Turn off polling, we do not want ATC polling to take place during

--  tasking operations. It causes infinite loops and other problems.

with System.Task_Primitives.Operations;

with System.Parameters;

with System.Traces;

with System.Soft_Links.Tasking;

package body System.Tasking.Protected_Objects is

   use System.Task_Primitives.Operations;

   use System.Traces;

   ----------------

   -- Local Data --

   ----------------

   Locking_Policy : Character;

   pragma Import (C, Locking_Policy, "__gl_locking_policy");

   -------------------------

   -- Finalize_Protection --

   -------------------------

   procedure Finalize_Protection (Object : in out Protection) is

   begin

      Finalize_Lock (Object.L'Unrestricted_Access);

   end Finalize_Protection;

   ---------------------------

   -- Initialize_Protection --

   ---------------------------

   procedure Initialize_Protection

     (Object           : Protection_Access;

      Ceiling_Priority : Integer)

   is

      Init_Priority : Integer := Ceiling_Priority;

   begin

      if Init_Priority = Unspecified_Priority then

         Init_Priority  := System.Priority'Last;

      end if;

      Initialize_Lock (Init_Priority, Object.L'Access);

      Object.Ceiling := System.Any_Priority (Init_Priority);

      Object.New_Ceiling := System.Any_Priority (Init_Priority);

      Object.Owner := Null_Task;

   end Initialize_Protection;

   -----------------

   -- Get_Ceiling --

   -----------------

   function Get_Ceiling

     (Object : Protection_Access) return System.Any_Priority is

   begin

      return Object.New_Ceiling;

   end Get_Ceiling;

   ----------

   -- Lock --

   ----------

   procedure Lock (Object : Protection_Access) is

      Ceiling_Violation : Boolean;

   begin

      --  The lock is made without deferring abort

      --  Therefore the abort has to be deferred before calling this routine.

      --  This means that the compiler has to generate a Defer_Abort call

      --  before the call to Lock.

      --  The caller is responsible for undeferring abort, and compiler

      --  generated calls must be protected with cleanup handlers to ensure

      --  that abort is undeferred in all cases.

      --  If pragma Detect_Blocking is active then, as described in the ARM

      --  9.5.1, par. 15, we must check whether this is an external call on a

      --  protected subprogram with the same target object as that of the

      --  protected action that is currently in progress (i.e., if the caller

      --  is already the protected object's owner). If this is the case hence

      --  Program_Error must be raised.

      if Detect_Blocking and then Object.Owner = Self then

         raise Program_Error;

      end if;

      Write_Lock (Object.L'Access, Ceiling_Violation);

      if Parameters.Runtime_Traces then

         Send_Trace_Info (PO_Lock);

      end if;

      if Ceiling_Violation then

         raise Program_Error;

      end if;

      --  We are entering in a protected action, so that we increase the

      --  protected object nesting level (if pragma Detect_Blocking is

      --  active), and update the protected object's owner.

      if Detect_Blocking then

         declare

            Self_Id : constant Task_Id := Self;

         begin

            --  Update the protected object's owner

            Object.Owner := Self_Id;

            --  Increase protected object nesting level

            Self_Id.Common.Protected_Action_Nesting :=

              Self_Id.Common.Protected_Action_Nesting + 1;

         end;

      end if;

   end Lock;

   --------------------

   -- Lock_Read_Only --

   --------------------

   procedure Lock_Read_Only (Object : Protection_Access) is

      Ceiling_Violation : Boolean;

   begin

      --  If pragma Detect_Blocking is active then, as described in the ARM

      --  9.5.1, par. 15, we must check whether this is an external call on

      --  protected subprogram with the same target object as that of the

      --  protected action that is currently in progress (i.e., if the caller

      --  is already the protected object's owner). If this is the case hence

      --  Program_Error must be raised.

      --

      --  Note that in this case (getting read access), several tasks may have

      --  read ownership of the protected object, so that this method of

      --  storing the (single) protected object's owner does not work reliably

      --  for read locks. However, this is the approach taken for two major

      --  reasons: first, this function is not currently being used (it is

      --  provided for possible future use), and second, it largely simplifies

      --  the implementation.

      if Detect_Blocking and then Object.Owner = Self then

         raise Program_Error;

      end if;

      Read_Lock (Object.L'Access, Ceiling_Violation);

      if Parameters.Runtime_Traces then

         Send_Trace_Info (PO_Lock);

      end if;

      if Ceiling_Violation then

         raise Program_Error;

      end if;

      --  We are entering in a protected action, so we increase the protected

      --  object nesting level (if pragma Detect_Blocking is active).

      if Detect_Blocking then

         declare

            Self_Id : constant Task_Id := Self;

         begin

            --  Update the protected object's owner

            Object.Owner := Self_Id;

            --  Increase protected object nesting level

            Self_Id.Common.Protected_Action_Nesting :=

              Self_Id.Common.Protected_Action_Nesting + 1;

         end;

      end if;

   end Lock_Read_Only;

   -----------------

   -- Set_Ceiling --

   -----------------

   procedure Set_Ceiling

     (Object : Protection_Access;

      Prio   : System.Any_Priority) is

   begin

      Object.New_Ceiling := Prio;

   end Set_Ceiling;

   ------------

   -- Unlock --

   ------------

   procedure Unlock (Object : Protection_Access) is

   begin

      --  We are exiting from a protected action, so that we decrease the

      --  protected object nesting level (if pragma Detect_Blocking is

      --  active), and remove ownership of the protected object.

      if Detect_Blocking then

         declare

            Self_Id : constant Task_Id := Self;

         begin

            --  Calls to this procedure can only take place when being within

            --  a protected action and when the caller is the protected

            --  object's owner.

            pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0

                             and then Object.Owner = Self_Id);

            --  Remove ownership of the protected object

            Object.Owner := Null_Task;

            --  We are exiting from a protected action, so we decrease the

            --  protected object nesting level.

            Self_Id.Common.Protected_Action_Nesting :=

              Self_Id.Common.Protected_Action_Nesting - 1;

         end;

      end if;

      --  Before releasing the mutex we must actually update its ceiling

      --  priority if it has been changed.

      if Object.New_Ceiling /= Object.Ceiling then

         if Locking_Policy = 'C' then

            System.Task_Primitives.Operations.Set_Ceiling

              (Object.L'Access, Object.New_Ceiling);

         end if;

         Object.Ceiling := Object.New_Ceiling;

      end if;

      Unlock (Object.L'Access);

      if Parameters.Runtime_Traces then

         Send_Trace_Info (PO_Unlock);

      end if;

   end Unlock;

begin

   --  Ensure that tasking is initialized, as well as tasking soft links

   --  when using protected objects.

   Tasking.Initialize;

   System.Soft_Links.Tasking.Init_Tasking_Soft_Links;

end System.Tasking.Protected_Objects;