gcc/ada/s-taprob.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
   4 --                                                                          --
   5 --      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     --
   6 --                                                                          --
   7 --                                  B o d y                                 --
   8 --                                                                          --
   9 --             Copyright (C) 1991-1994, Florida State University            --
  10 --                     Copyright (C) 1995-2008, AdaCore                     --
  11 --                                                                          --
  12 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  20 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  21 -- Boston, MA 02110-1301, USA.                                              --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNARL was developed by the GNARL team at Florida State University.       --
  31 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 pragma Polling (Off);
  36 --  Turn off polling, we do not want ATC polling to take place during
  37 --  tasking operations. It causes infinite loops and other problems.
  38
  39 with System.Task_Primitives.Operations;
  40 with System.Parameters;
  41 with System.Traces;
  42 with System.Soft_Links.Tasking;
  43
  44 package body System.Tasking.Protected_Objects is
  45
  46    use System.Task_Primitives.Operations;
  47    use System.Traces;
  48
  49    ----------------
  50    -- Local Data --
  51    ----------------
  52
  53    Locking_Policy : Character;
  54    pragma Import (C, Locking_Policy, "__gl_locking_policy");
  55
  56    -------------------------
  57    -- Finalize_Protection --
  58    -------------------------
  59
  60    procedure Finalize_Protection (Object : in out Protection) is
  61    begin
  62       Finalize_Lock (Object.L'Unrestricted_Access);
  63    end Finalize_Protection;
  64
  65    ---------------------------
  66    -- Initialize_Protection --
  67    ---------------------------
  68
  69    procedure Initialize_Protection
  70      (Object           : Protection_Access;
  71       Ceiling_Priority : Integer)
  72    is
  73       Init_Priority : Integer := Ceiling_Priority;
  74
  75    begin
  76       if Init_Priority = Unspecified_Priority then
  77          Init_Priority  := System.Priority'Last;
  78       end if;
  79
  80       Initialize_Lock (Init_Priority, Object.L'Access);
  81       Object.Ceiling := System.Any_Priority (Init_Priority);
  82       Object.New_Ceiling := System.Any_Priority (Init_Priority);
  83       Object.Owner := Null_Task;
  84    end Initialize_Protection;
  85
  86    -----------------
  87    -- Get_Ceiling --
  88    -----------------
  89
  90    function Get_Ceiling
  91      (Object : Protection_Access) return System.Any_Priority is
  92    begin
  93       return Object.New_Ceiling;
  94    end Get_Ceiling;
  95
  96    ----------
  97    -- Lock --
  98    ----------
  99
 100    procedure Lock (Object : Protection_Access) is
 101       Ceiling_Violation : Boolean;
 102
 103    begin
 104       --  The lock is made without deferring abort
 105
 106       --  Therefore the abort has to be deferred before calling this routine.
 107       --  This means that the compiler has to generate a Defer_Abort call
 108       --  before the call to Lock.
 109
 110       --  The caller is responsible for undeferring abort, and compiler
 111       --  generated calls must be protected with cleanup handlers to ensure
 112       --  that abort is undeferred in all cases.
 113
 114       --  If pragma Detect_Blocking is active then, as described in the ARM
 115       --  9.5.1, par. 15, we must check whether this is an external call on a
 116       --  protected subprogram with the same target object as that of the
 117       --  protected action that is currently in progress (i.e., if the caller
 118       --  is already the protected object's owner). If this is the case hence
 119       --  Program_Error must be raised.
 120
 121       if Detect_Blocking and then Object.Owner = Self then
 122          raise Program_Error;
 123       end if;
 124
 125       Write_Lock (Object.L'Access, Ceiling_Violation);
 126
 127       if Parameters.Runtime_Traces then
 128          Send_Trace_Info (PO_Lock);
 129       end if;
 130
 131       if Ceiling_Violation then
 132          raise Program_Error;
 133       end if;
 134
 135       --  We are entering in a protected action, so that we increase the
 136       --  protected object nesting level (if pragma Detect_Blocking is
 137       --  active), and update the protected object's owner.
 138
 139       if Detect_Blocking then
 140          declare
 141             Self_Id : constant Task_Id := Self;
 142          begin
 143             --  Update the protected object's owner
 144
 145             Object.Owner := Self_Id;
 146
 147             --  Increase protected object nesting level
 148
 149             Self_Id.Common.Protected_Action_Nesting :=
 150               Self_Id.Common.Protected_Action_Nesting + 1;
 151          end;
 152       end if;
 153    end Lock;
 154
 155    --------------------
 156    -- Lock_Read_Only --
 157    --------------------
 158
 159    procedure Lock_Read_Only (Object : Protection_Access) is
 160       Ceiling_Violation : Boolean;
 161
 162    begin
 163       --  If pragma Detect_Blocking is active then, as described in the ARM
 164       --  9.5.1, par. 15, we must check whether this is an external call on
 165       --  protected subprogram with the same target object as that of the
 166       --  protected action that is currently in progress (i.e., if the caller
 167       --  is already the protected object's owner). If this is the case hence
 168       --  Program_Error must be raised.
 169       --
 170       --  Note that in this case (getting read access), several tasks may have
 171       --  read ownership of the protected object, so that this method of
 172       --  storing the (single) protected object's owner does not work reliably
 173       --  for read locks. However, this is the approach taken for two major
 174       --  reasons: first, this function is not currently being used (it is
 175       --  provided for possible future use), and second, it largely simplifies
 176       --  the implementation.
 177
 178       if Detect_Blocking and then Object.Owner = Self then
 179          raise Program_Error;
 180       end if;
 181
 182       Read_Lock (Object.L'Access, Ceiling_Violation);
 183
 184       if Parameters.Runtime_Traces then
 185          Send_Trace_Info (PO_Lock);
 186       end if;
 187
 188       if Ceiling_Violation then
 189          raise Program_Error;
 190       end if;
 191
 192       --  We are entering in a protected action, so we increase the protected
 193       --  object nesting level (if pragma Detect_Blocking is active).
 194
 195       if Detect_Blocking then
 196          declare
 197             Self_Id : constant Task_Id := Self;
 198          begin
 199             --  Update the protected object's owner
 200
 201             Object.Owner := Self_Id;
 202
 203             --  Increase protected object nesting level
 204
 205             Self_Id.Common.Protected_Action_Nesting :=
 206               Self_Id.Common.Protected_Action_Nesting + 1;
 207          end;
 208       end if;
 209    end Lock_Read_Only;
 210
 211    -----------------
 212    -- Set_Ceiling --
 213    -----------------
 214
 215    procedure Set_Ceiling
 216      (Object : Protection_Access;
 217       Prio   : System.Any_Priority) is
 218    begin
 219       Object.New_Ceiling := Prio;
 220    end Set_Ceiling;
 221
 222    ------------
 223    -- Unlock --
 224    ------------
 225
 226    procedure Unlock (Object : Protection_Access) is
 227    begin
 228       --  We are exiting from a protected action, so that we decrease the
 229       --  protected object nesting level (if pragma Detect_Blocking is
 230       --  active), and remove ownership of the protected object.
 231
 232       if Detect_Blocking then
 233          declare
 234             Self_Id : constant Task_Id := Self;
 235
 236          begin
 237             --  Calls to this procedure can only take place when being within
 238             --  a protected action and when the caller is the protected
 239             --  object's owner.
 240
 241             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 242                              and then Object.Owner = Self_Id);
 243
 244             --  Remove ownership of the protected object
 245
 246             Object.Owner := Null_Task;
 247
 248             --  We are exiting from a protected action, so we decrease the
 249             --  protected object nesting level.
 250
 251             Self_Id.Common.Protected_Action_Nesting :=
 252               Self_Id.Common.Protected_Action_Nesting - 1;
 253          end;
 254       end if;
 255
 256       --  Before releasing the mutex we must actually update its ceiling
 257       --  priority if it has been changed.
 258
 259       if Object.New_Ceiling /= Object.Ceiling then
 260          if Locking_Policy = 'C' then
 261             System.Task_Primitives.Operations.Set_Ceiling
 262               (Object.L'Access, Object.New_Ceiling);
 263          end if;
 264
 265          Object.Ceiling := Object.New_Ceiling;
 266       end if;
 267
 268       Unlock (Object.L'Access);
 269
 270       if Parameters.Runtime_Traces then
 271          Send_Trace_Info (PO_Unlock);
 272       end if;
 273    end Unlock;
 274
 275 begin
 276    --  Ensure that tasking is initialized, as well as tasking soft links
 277    --  when using protected objects.
 278
 279    Tasking.Initialize;
 280    System.Soft_Links.Tasking.Init_Tasking_Soft_Links;
 281 end System.Tasking.Protected_Objects;