gcc/ada/a-dynpri.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                  GNAT 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 --          Copyright (C) 1992-2009, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNARL was developed by the GNARL team at Florida State University.       --
  28 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 with System.Task_Primitives.Operations;
  33 with System.Tasking;
  34 with System.Parameters;
  35 with System.Soft_Links;
  36
  37 with Ada.Unchecked_Conversion;
  38
  39 package body Ada.Dynamic_Priorities is
  40
  41    package STPO renames System.Task_Primitives.Operations;
  42    package SSL renames System.Soft_Links;
  43
  44    use System.Parameters;
  45    use System.Tasking;
  46
  47    function Convert_Ids is new
  48      Ada.Unchecked_Conversion
  49        (Task_Identification.Task_Id, System.Tasking.Task_Id);
  50
  51    ------------------
  52    -- Get_Priority --
  53    ------------------
  54
  55    --  Inquire base priority of a task
  56
  57    function Get_Priority
  58      (T : Ada.Task_Identification.Task_Id :=
  59         Ada.Task_Identification.Current_Task) return System.Any_Priority
  60    is
  61       Target : constant Task_Id := Convert_Ids (T);
  62       Error_Message : constant String := "Trying to get the priority of a ";
  63
  64    begin
  65       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
  66          raise Program_Error with Error_Message & "null task";
  67       end if;
  68
  69       if Task_Identification.Is_Terminated (T) then
  70          raise Tasking_Error with Error_Message & "terminated task";
  71       end if;
  72
  73       return Target.Common.Base_Priority;
  74    end Get_Priority;
  75
  76    ------------------
  77    -- Set_Priority --
  78    ------------------
  79
  80    --  Change base priority of a task dynamically
  81
  82    procedure Set_Priority
  83      (Priority : System.Any_Priority;
  84       T        : Ada.Task_Identification.Task_Id :=
  85                    Ada.Task_Identification.Current_Task)
  86    is
  87       Target        : constant Task_Id := Convert_Ids (T);
  88       Error_Message : constant String := "Trying to set the priority of a ";
  89       Yield_Needed  : Boolean;
  90
  91    begin
  92       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
  93          raise Program_Error with Error_Message & "null task";
  94       end if;
  95
  96       --  Setting the priority of an already-terminated task doesn't do
  97       --  anything (see RM-D.5.1(7)). Note that Get_Priority is different in
  98       --  this regard.
  99
 100       if Task_Identification.Is_Terminated (T) then
 101          return;
 102       end if;
 103
 104       SSL.Abort_Defer.all;
 105
 106       if Single_Lock then
 107          STPO.Lock_RTS;
 108       end if;
 109
 110       STPO.Write_Lock (Target);
 111
 112       Target.Common.Base_Priority := Priority;
 113
 114       if Target.Common.Call /= null
 115         and then
 116           Target.Common.Call.Acceptor_Prev_Priority /= Priority_Not_Boosted
 117       then
 118          --  Target is within a rendezvous, so ensure the correct priority
 119          --  will be reset when finishing the rendezvous, and only change the
 120          --  priority immediately if the new priority is greater than the
 121          --  current (inherited) priority.
 122
 123          Target.Common.Call.Acceptor_Prev_Priority := Priority;
 124
 125          if Priority >= Target.Common.Current_Priority then
 126             Yield_Needed := True;
 127             STPO.Set_Priority (Target, Priority);
 128          else
 129             Yield_Needed := False;
 130          end if;
 131
 132       else
 133          Yield_Needed := True;
 134          STPO.Set_Priority (Target, Priority);
 135
 136          if Target.Common.State = Entry_Caller_Sleep then
 137             Target.Pending_Priority_Change := True;
 138             STPO.Wakeup (Target, Target.Common.State);
 139          end if;
 140       end if;
 141
 142       STPO.Unlock (Target);
 143
 144       if Single_Lock then
 145          STPO.Unlock_RTS;
 146       end if;
 147
 148       if STPO.Self = Target and then Yield_Needed then
 149
 150          --  Yield is needed to enforce FIFO task dispatching
 151
 152          --  LL Set_Priority is made while holding the RTS lock so that it is
 153          --  inheriting high priority until it release all the RTS locks.
 154
 155          --  If this is used in a system where Ceiling Locking is not enforced
 156          --  we may end up getting two Yield effects.
 157
 158          STPO.Yield;
 159       end if;
 160
 161       SSL.Abort_Undefer.all;
 162    end Set_Priority;
 163
 164 end Ada.Dynamic_Priorities;