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                                 --
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   9 --          Copyright (C) 1992-2007, Free Software Foundation, Inc.         --
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  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
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  27 -- covered by the  GNU Public License.                                      --
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  29 -- GNARL was developed by the GNARL team at Florida State University.       --
  30 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 with System.Task_Primitives.Operations;
  35 --  used for Write_Lock
  36 --           Unlock
  37 --           Set_Priority
  38 --           Wakeup
  39 --           Self
  40
  41 with System.Tasking;
  42 --  used for Task_Id
  43
  44 with System.Parameters;
  45 --  used for Single_Lock
  46
  47 with System.Soft_Links;
  48 --  use for Abort_Defer
  49 --          Abort_Undefer
  50
  51 with Ada.Unchecked_Conversion;
  52
  53 package body Ada.Dynamic_Priorities is
  54
  55    package STPO renames System.Task_Primitives.Operations;
  56    package SSL renames System.Soft_Links;
  57
  58    use System.Parameters;
  59    use System.Tasking;
  60
  61    function Convert_Ids is new
  62      Ada.Unchecked_Conversion
  63        (Task_Identification.Task_Id, System.Tasking.Task_Id);
  64
  65    ------------------
  66    -- Get_Priority --
  67    ------------------
  68
  69    --  Inquire base priority of a task
  70
  71    function Get_Priority
  72      (T : Ada.Task_Identification.Task_Id :=
  73         Ada.Task_Identification.Current_Task) return System.Any_Priority
  74    is
  75       Target : constant Task_Id := Convert_Ids (T);
  76       Error_Message : constant String := "Trying to get the priority of a ";
  77
  78    begin
  79       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
  80          raise Program_Error with Error_Message & "null task";
  81       end if;
  82
  83       if Task_Identification.Is_Terminated (T) then
  84          raise Tasking_Error with Error_Message & "null task";
  85       end if;
  86
  87       return Target.Common.Base_Priority;
  88    end Get_Priority;
  89
  90    ------------------
  91    -- Set_Priority --
  92    ------------------
  93
  94    --  Change base priority of a task dynamically
  95
  96    procedure Set_Priority
  97      (Priority : System.Any_Priority;
  98       T        : Ada.Task_Identification.Task_Id :=
  99                    Ada.Task_Identification.Current_Task)
 100    is
 101       Target        : constant Task_Id := Convert_Ids (T);
 102       Error_Message : constant String := "Trying to set the priority of a ";
 103       Yield_Needed  : Boolean;
 104
 105    begin
 106       if Target = Convert_Ids (Ada.Task_Identification.Null_Task_Id) then
 107          raise Program_Error with Error_Message & "null task";
 108       end if;
 109
 110       if Task_Identification.Is_Terminated (T) then
 111          raise Tasking_Error with Error_Message & "terminated task";
 112       end if;
 113
 114       SSL.Abort_Defer.all;
 115
 116       if Single_Lock then
 117          STPO.Lock_RTS;
 118       end if;
 119
 120       STPO.Write_Lock (Target);
 121
 122       Target.Common.Base_Priority := Priority;
 123
 124       if Target.Common.Call /= null
 125         and then
 126           Target.Common.Call.Acceptor_Prev_Priority /= Priority_Not_Boosted
 127       then
 128          --  Target is within a rendezvous, so ensure the correct priority
 129          --  will be reset when finishing the rendezvous, and only change the
 130          --  priority immediately if the new priority is greater than the
 131          --  current (inherited) priority.
 132
 133          Target.Common.Call.Acceptor_Prev_Priority := Priority;
 134
 135          if Priority >= Target.Common.Current_Priority then
 136             Yield_Needed := True;
 137             STPO.Set_Priority (Target, Priority);
 138          else
 139             Yield_Needed := False;
 140          end if;
 141
 142       else
 143          Yield_Needed := True;
 144          STPO.Set_Priority (Target, Priority);
 145
 146          if Target.Common.State = Entry_Caller_Sleep then
 147             Target.Pending_Priority_Change := True;
 148             STPO.Wakeup (Target, Target.Common.State);
 149          end if;
 150       end if;
 151
 152       STPO.Unlock (Target);
 153
 154       if Single_Lock then
 155          STPO.Unlock_RTS;
 156       end if;
 157
 158       if STPO.Self = Target and then Yield_Needed then
 159
 160          --  Yield is needed to enforce FIFO task dispatching
 161
 162          --  LL Set_Priority is made while holding the RTS lock so that it is
 163          --  inheriting high priority until it release all the RTS locks.
 164
 165          --  If this is used in a system where Ceiling Locking is not enforced
 166          --  we may end up getting two Yield effects.
 167
 168          STPO.Yield;
 169       end if;
 170
 171       SSL.Abort_Undefer.all;
 172    end Set_Priority;
 173
 174 end Ada.Dynamic_Priorities;