gcc/ada/a-dynpri.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS              --
   4 --                                                                          --
   5 --                 A D A . D Y N A M I C _ P R I O R I T I E S              --
   6 --                                                                          --
   7 --                                  B o d y                                 --
   8 --                                                                          --
   9 --                             $Revision: 1.25 $
  10 --                                                                          --
  11 --             Copyright (C) 1991-2001 Florida State University             --
  12 --                                                                          --
  13 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNARL was developed by the GNARL team at Florida State University. It is --
  32 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  33 -- State University (http://www.gnat.com).                                  --
  34 --                                                                          --
  35 ------------------------------------------------------------------------------
  36
  37 with Ada.Task_Identification;
  38 --  used for Task_Id
  39 --           Current_Task
  40 --           Null_Task_Id
  41 --           Is_Terminated
  42
  43 with System.Task_Primitives.Operations;
  44 --  used for Write_Lock
  45 --           Unlock
  46 --           Set_Priority
  47 --           Wakeup
  48 --           Self
  49
  50 with System.Tasking;
  51 --  used for Task_ID
  52
  53 with Ada.Exceptions;
  54 --  used for Raise_Exception
  55
  56 with System.Tasking.Initialization;
  57 --  used for Defer/Undefer_Abort
  58
  59 with Unchecked_Conversion;
  60
  61 package body Ada.Dynamic_Priorities is
  62
  63    use System.Tasking;
  64    use Ada.Exceptions;
  65
  66    function Convert_Ids is new
  67      Unchecked_Conversion
  68        (Task_Identification.Task_Id, System.Tasking.Task_ID);
  69
  70    ------------------
  71    -- Get_Priority --
  72    ------------------
  73
  74    --  Inquire base priority of a task
  75
  76    function Get_Priority
  77      (T : Ada.Task_Identification.Task_Id :=
  78           Ada.Task_Identification.Current_Task)
  79       return System.Any_Priority is
  80
  81       Target : constant Task_ID := Convert_Ids (T);
  82       Error_Message : constant String := "Trying to get the priority of a ";
  83
  84    begin
  85       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
  86          Raise_Exception (Program_Error'Identity,
  87            Error_Message & "null task");
  88       end if;
  89
  90       if Task_Identification.Is_Terminated (T) then
  91          Raise_Exception (Tasking_Error'Identity,
  92            Error_Message & "null task");
  93       end if;
  94
  95       return Target.Common.Base_Priority;
  96    end Get_Priority;
  97
  98    ------------------
  99    -- Set_Priority --
 100    ------------------
 101
 102    --  Change base priority of a task dynamically
 103
 104    procedure Set_Priority
 105      (Priority : System.Any_Priority;
 106       T : Ada.Task_Identification.Task_Id :=
 107           Ada.Task_Identification.Current_Task)
 108    is
 109       Target  : constant Task_ID := Convert_Ids (T);
 110       Self_ID : constant Task_ID := System.Task_Primitives.Operations.Self;
 111       Error_Message : constant String := "Trying to set the priority of a ";
 112
 113    begin
 114       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
 115          Raise_Exception (Program_Error'Identity,
 116            Error_Message & "null task");
 117       end if;
 118
 119       if Task_Identification.Is_Terminated (T) then
 120          Raise_Exception (Tasking_Error'Identity,
 121            Error_Message & "terminated task");
 122       end if;
 123
 124       System.Tasking.Initialization.Defer_Abort (Self_ID);
 125       System.Task_Primitives.Operations.Write_Lock (Target);
 126
 127       if Self_ID = Target then
 128          Target.Common.Base_Priority := Priority;
 129          System.Task_Primitives.Operations.Set_Priority (Target, Priority);
 130          System.Task_Primitives.Operations.Unlock (Target);
 131          System.Task_Primitives.Operations.Yield;
 132          --  Yield is needed to enforce FIFO task dispatching.
 133          --  LL Set_Priority is made while holding the RTS lock so that
 134          --  it is inheriting high priority until it release all the RTS
 135          --  locks.
 136          --  If this is used in a system where Ceiling Locking is
 137          --  not enforced we may end up getting two Yield effects.
 138       else
 139          Target.New_Base_Priority := Priority;
 140          Target.Pending_Priority_Change := True;
 141          Target.Pending_Action := True;
 142
 143          System.Task_Primitives.Operations.Wakeup
 144            (Target, Target.Common.State);
 145          --  If the task is suspended, wake it up to perform the change.
 146          --  check for ceiling violations ???
 147          System.Task_Primitives.Operations.Unlock (Target);
 148
 149       end if;
 150       System.Tasking.Initialization.Undefer_Abort (Self_ID);
 151
 152    end Set_Priority;
 153
 154 end Ada.Dynamic_Priorities;