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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     --

--                                                                          --

--                                  S p e c                                 --

--                                                                          --

--          Copyright (C) 1992-2009, Free Software Foundation, Inc.         --

--                                                                          --

-- 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 3,  or (at your option) any later ver- --

-- sion.  GNAT 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.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

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

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

--                                                                          --

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

--  This package provides necessary definitions to handle simple (i.e without

--  entries) protected objects.

--  All the routines that handle protected objects with entries have been moved

--  to two children: Entries and Operations. Note that Entries only contains

--  the type declaration and the OO primitives. This is needed to avoid

--  circular dependency.

--  This package is part of the high level tasking interface used by the

--  compiler to expand Ada 95 tasking constructs into simpler run time calls

--  (aka GNARLI, GNU Ada Run-time Library Interface)

--  Note: the compiler generates direct calls to this interface, via Rtsfind.

--  Any changes to this interface may require corresponding compiler changes

--  in exp_ch9.adb and possibly exp_ch7.adb and exp_attr.adb

package System.Tasking.Protected_Objects is

   pragma Elaborate_Body;

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

   -- Compiler Interface (GNARLI) --

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

   --  The compiler will expand in the GNAT tree the following construct:

   --  protected PO is

   --     procedure P;

   --  private

   --     open : boolean := false;

   --  end PO;

   --  protected body PO is

   --     procedure P is

   --        ...variable declarations...

   --     begin

   --        ...B...

   --     end P;

   --  end PO;

   --  as follows:

   --  protected type poT is

   --     procedure p;

   --  private

   --     open : boolean := false;

   --  end poT;

   --  type poTV is limited record

   --     open : boolean := false;

   --     _object : aliased protection;

   --  end record;

   --  procedure poPT__pN (_object : in out poTV);

   --  procedure poPT__pP (_object : in out poTV);

   --  freeze poTV [

   --     procedure poTVI (_init : in out poTV) is

   --     begin

   --        _init.open := false;

   --        object-init-proc (_init._object);

   --        initialize_protection (_init._object'unchecked_access,

   --          unspecified_priority);

   --        return;

   --     end _init_proc;

   --  ]

   --  po : poT;

   --  poTVI (poTV!(po));

   --  procedure poPT__pN (_object : in out poTV) is

   --     poR : protection renames _object._object;

   --     openP : boolean renames _object.open;

   --     ...variable declarations...

   --  begin

   --     ...B...

   --     return;

   --  end poPT__pN;

   --  procedure poPT__pP (_object : in out poTV) is

   --     procedure _clean is

   --     begin

   --        unlock (_object._object'unchecked_access);

   --        return;

   --     end _clean;

   --  begin

   --     lock (_object._object'unchecked_access);

   --     B2b : begin

   --        poPT__pN (_object);

   --     at end

   --        _clean;

   --     end B2b;

   --     return;

   --  end poPT__pP;

   Null_Protected_Entry : constant := Null_Entry;

   Max_Protected_Entry : constant := Max_Entry;

   type Protected_Entry_Index is new Entry_Index

     range Null_Protected_Entry .. Max_Protected_Entry;

   type Barrier_Function_Pointer is access

     function

       (O    : System.Address;

        E    : Protected_Entry_Index)

        return Boolean;

   --  Pointer to a function which evaluates the barrier of a protected

   --  entry body. O is a pointer to the compiler-generated record

   --  representing the protected object, and E is the index of the

   --  entry serviced by the body.

   type Entry_Action_Pointer is access

     procedure

       (O : System.Address;

        P : System.Address;

        E : Protected_Entry_Index);

   --  Pointer to a procedure which executes the sequence of statements

   --  of a protected entry body. O is a pointer to the compiler-generated

   --  record representing the protected object, P is a pointer to the

   --  record of entry parameters, and E is the index of the

   --  entry serviced by the body.

   type Entry_Body is record

      Barrier : Barrier_Function_Pointer;

      Action  : Entry_Action_Pointer;

   end record;

   --  The compiler-generated code passes objects of this type to the GNARL

   --  to allow it to access the executable code of an entry body.

   type Entry_Body_Access is access all Entry_Body;

   type Protection is limited private;

   --  This type contains the GNARL state of a protected object. The

   --  application-defined portion of the state (i.e. private objects)

   --  is maintained by the compiler-generated code.

   --  Note that there are now 2 Protection types. One for the simple

   --  case (no entries) and one for the general case that needs the whole

   --  Finalization mechanism.

   --  This split helps in the case of restricted run time where we want to

   --  minimize the size of the code.

   type Protection_Access is access all Protection;

   Null_PO : constant Protection_Access := null;

   function Get_Ceiling

     (Object : Protection_Access) return System.Any_Priority;

   --  Returns the new ceiling priority of the protected object

   procedure Initialize_Protection

     (Object           : Protection_Access;

      Ceiling_Priority : Integer);

   --  Initialize the Object parameter so that it can be used by the runtime

   --  to keep track of the runtime state of a protected object.

   procedure Lock (Object : Protection_Access);

   --  Lock a protected object for write access. Upon return, the caller

   --  owns the lock to this object, and no other call to Lock or

   --  Lock_Read_Only with the same argument will return until the

   --  corresponding call to Unlock has been made by the caller.

   procedure Lock_Read_Only (Object : Protection_Access);

   --  Lock a protected object for read access. Upon return, the caller

   --  owns the lock for read access, and no other calls to Lock with the

   --  same argument will return until the corresponding call to Unlock

   --  has been made by the caller. Other calls to Lock_Read_Only may (but

   --  need not) return before the call to Unlock, and the corresponding

   --  callers will also own the lock for read access.

   --

   --  Note: we are not currently using this interface, it is provided

   --  for possible future use. At the current time, everyone uses Lock

   --  for both read and write locks.

   procedure Set_Ceiling

     (Object : Protection_Access;

      Prio   : System.Any_Priority);

   --  Sets the new ceiling priority of the protected object

   procedure Unlock (Object : Protection_Access);

   --  Relinquish ownership of the lock for the object represented by

   --  the Object parameter. If this ownership was for write access, or

   --  if it was for read access where there are no other read access

   --  locks outstanding, one (or more, in the case of Lock_Read_Only)

   --  of the tasks waiting on this lock (if any) will be given the

   --  lock and allowed to return from the Lock or Lock_Read_Only call.

private

   type Protection is record

      L : aliased Task_Primitives.Lock;

      --  Lock used to ensure mutual exclusive access to the protected object

      Ceiling : System.Any_Priority;

      --  Ceiling priority associated to the protected object

      New_Ceiling : System.Any_Priority;

      --  New ceiling priority associated to the protected object. In case

      --  of assignment of a new ceiling priority to the protected object the

      --  frontend generates a call to set_ceiling to save the new value in

      --  this field. After such assignment this value can be read by means

      --  of the 'Priority attribute, which generates a call to get_ceiling.

      --  However, the ceiling of the protected object will not be changed

      --  until completion of the protected action in which the assignment

      --  has been executed (AARM D.5.2 (10/2)).

      Owner : Task_Id;

      --  This field contains the protected object's owner. Null_Task

      --  indicates that the protected object is not currently being used.

      --  This information is used for detecting the type of potentially

      --  blocking operations described in the ARM 9.5.1, par. 15 (external

      --  calls on a protected subprogram with the same target object as that

      --  of the protected action).

   end record;

   procedure Finalize_Protection (Object : in out Protection);

   --  Clean up a Protection object (in particular, finalize the associated

   --  Lock object). The compiler generates calls automatically to this

   --  procedure

end System.Tasking.Protected_Objects;