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) 1995-2011, AdaCore                     --
  11 --                                                                          --
  12 -- GNAT 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 3,  or (at your option) any later ver- --
  15 -- sion.  GNAT 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.                                     --
  18 --                                                                          --
  19 -- As a special exception under Section 7 of GPL version 3, you are granted --
  20 -- additional permissions described in the GCC Runtime Library Exception,   --
  21 -- version 3.1, as published by the Free Software Foundation.               --
  22 --                                                                          --
  23 -- You should have received a copy of the GNU General Public License and    --
  24 -- a copy of the GCC Runtime Library Exception along with this program;     --
  25 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  26 -- <http://www.gnu.org/licenses/>.                                          --
  27 --                                                                          --
  28 -- GNARL was developed by the GNARL team at Florida State University.       --
  29 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  30 --                                                                          --
  31 ------------------------------------------------------------------------------
  32
  33 pragma Polling (Off);
  34 --  Turn off polling, we do not want ATC polling to take place during
  35 --  tasking operations. It causes infinite loops and other problems.
  36
  37 with System.Task_Primitives.Operations;
  38 with System.Parameters;
  39 with System.Traces;
  40 with System.Soft_Links.Tasking;
  41
  42 package body System.Tasking.Protected_Objects is
  43
  44    use System.Task_Primitives.Operations;
  45    use System.Traces;
  46
  47    ----------------
  48    -- Local Data --
  49    ----------------
  50
  51    Locking_Policy : Character;
  52    pragma Import (C, Locking_Policy, "__gl_locking_policy");
  53
  54    -------------------------
  55    -- Finalize_Protection --
  56    -------------------------
  57
  58    procedure Finalize_Protection (Object : in out Protection) is
  59    begin
  60       Finalize_Lock (Object.L'Unrestricted_Access);
  61    end Finalize_Protection;
  62
  63    ---------------------------
  64    -- Initialize_Protection --
  65    ---------------------------
  66
  67    procedure Initialize_Protection
  68      (Object           : Protection_Access;
  69       Ceiling_Priority : Integer)
  70    is
  71       Init_Priority : Integer := Ceiling_Priority;
  72
  73    begin
  74       if Init_Priority = Unspecified_Priority then
  75          Init_Priority  := System.Priority'Last;
  76       end if;
  77
  78       Initialize_Lock (Init_Priority, Object.L'Access);
  79       Object.Ceiling := System.Any_Priority (Init_Priority);
  80       Object.New_Ceiling := System.Any_Priority (Init_Priority);
  81       Object.Owner := Null_Task;
  82    end Initialize_Protection;
  83
  84    -----------------
  85    -- Get_Ceiling --
  86    -----------------
  87
  88    function Get_Ceiling
  89      (Object : Protection_Access) return System.Any_Priority is
  90    begin
  91       return Object.New_Ceiling;
  92    end Get_Ceiling;
  93
  94    ----------
  95    -- Lock --
  96    ----------
  97
  98    procedure Lock (Object : Protection_Access) is
  99       Ceiling_Violation : Boolean;
 100
 101    begin
 102       --  The lock is made without deferring abort
 103
 104       --  Therefore the abort has to be deferred before calling this routine.
 105       --  This means that the compiler has to generate a Defer_Abort call
 106       --  before the call to Lock.
 107
 108       --  The caller is responsible for undeferring abort, and compiler
 109       --  generated calls must be protected with cleanup handlers to ensure
 110       --  that abort is undeferred in all cases.
 111
 112       --  If pragma Detect_Blocking is active then, as described in the ARM
 113       --  9.5.1, par. 15, we must check whether this is an external call on a
 114       --  protected subprogram with the same target object as that of the
 115       --  protected action that is currently in progress (i.e., if the caller
 116       --  is already the protected object's owner). If this is the case hence
 117       --  Program_Error must be raised.
 118
 119       if Detect_Blocking and then Object.Owner = Self then
 120          raise Program_Error;
 121       end if;
 122
 123       Write_Lock (Object.L'Access, Ceiling_Violation);
 124
 125       if Parameters.Runtime_Traces then
 126          Send_Trace_Info (PO_Lock);
 127       end if;
 128
 129       if Ceiling_Violation then
 130          raise Program_Error;
 131       end if;
 132
 133       --  We are entering in a protected action, so that we increase the
 134       --  protected object nesting level (if pragma Detect_Blocking is
 135       --  active), and update the protected object's owner.
 136
 137       if Detect_Blocking then
 138          declare
 139             Self_Id : constant Task_Id := Self;
 140          begin
 141             --  Update the protected object's owner
 142
 143             Object.Owner := Self_Id;
 144
 145             --  Increase protected object nesting level
 146
 147             Self_Id.Common.Protected_Action_Nesting :=
 148               Self_Id.Common.Protected_Action_Nesting + 1;
 149          end;
 150       end if;
 151    end Lock;
 152
 153    --------------------
 154    -- Lock_Read_Only --
 155    --------------------
 156
 157    procedure Lock_Read_Only (Object : Protection_Access) is
 158       Ceiling_Violation : Boolean;
 159
 160    begin
 161       --  If pragma Detect_Blocking is active then, as described in the ARM
 162       --  9.5.1, par. 15, we must check whether this is an external call on
 163       --  protected subprogram with the same target object as that of the
 164       --  protected action that is currently in progress (i.e., if the caller
 165       --  is already the protected object's owner). If this is the case hence
 166       --  Program_Error must be raised.
 167       --
 168       --  Note that in this case (getting read access), several tasks may have
 169       --  read ownership of the protected object, so that this method of
 170       --  storing the (single) protected object's owner does not work reliably
 171       --  for read locks. However, this is the approach taken for two major
 172       --  reasons: first, this function is not currently being used (it is
 173       --  provided for possible future use), and second, it largely simplifies
 174       --  the implementation.
 175
 176       if Detect_Blocking and then Object.Owner = Self then
 177          raise Program_Error;
 178       end if;
 179
 180       Read_Lock (Object.L'Access, Ceiling_Violation);
 181
 182       if Parameters.Runtime_Traces then
 183          Send_Trace_Info (PO_Lock);
 184       end if;
 185
 186       if Ceiling_Violation then
 187          raise Program_Error;
 188       end if;
 189
 190       --  We are entering in a protected action, so we increase the protected
 191       --  object nesting level (if pragma Detect_Blocking is active).
 192
 193       if Detect_Blocking then
 194          declare
 195             Self_Id : constant Task_Id := Self;
 196          begin
 197             --  Update the protected object's owner
 198
 199             Object.Owner := Self_Id;
 200
 201             --  Increase protected object nesting level
 202
 203             Self_Id.Common.Protected_Action_Nesting :=
 204               Self_Id.Common.Protected_Action_Nesting + 1;
 205          end;
 206       end if;
 207    end Lock_Read_Only;
 208
 209    -----------------
 210    -- Set_Ceiling --
 211    -----------------
 212
 213    procedure Set_Ceiling
 214      (Object : Protection_Access;
 215       Prio   : System.Any_Priority) is
 216    begin
 217       Object.New_Ceiling := Prio;
 218    end Set_Ceiling;
 219
 220    ------------
 221    -- Unlock --
 222    ------------
 223
 224    procedure Unlock (Object : Protection_Access) is
 225    begin
 226       --  We are exiting from a protected action, so that we decrease the
 227       --  protected object nesting level (if pragma Detect_Blocking is
 228       --  active), and remove ownership of the protected object.
 229
 230       if Detect_Blocking then
 231          declare
 232             Self_Id : constant Task_Id := Self;
 233
 234          begin
 235             --  Calls to this procedure can only take place when being within
 236             --  a protected action and when the caller is the protected
 237             --  object's owner.
 238
 239             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 240                              and then Object.Owner = Self_Id);
 241
 242             --  Remove ownership of the protected object
 243
 244             Object.Owner := Null_Task;
 245
 246             --  We are exiting from a protected action, so we decrease the
 247             --  protected object nesting level.
 248
 249             Self_Id.Common.Protected_Action_Nesting :=
 250               Self_Id.Common.Protected_Action_Nesting - 1;
 251          end;
 252       end if;
 253
 254       --  Before releasing the mutex we must actually update its ceiling
 255       --  priority if it has been changed.
 256
 257       if Object.New_Ceiling /= Object.Ceiling then
 258          if Locking_Policy = 'C' then
 259             System.Task_Primitives.Operations.Set_Ceiling
 260               (Object.L'Access, Object.New_Ceiling);
 261          end if;
 262
 263          Object.Ceiling := Object.New_Ceiling;
 264       end if;
 265
 266       Unlock (Object.L'Access);
 267
 268       if Parameters.Runtime_Traces then
 269          Send_Trace_Info (PO_Unlock);
 270       end if;
 271    end Unlock;
 272
 273 begin
 274    --  Ensure that tasking is initialized, as well as tasking soft links
 275    --  when using protected objects.
 276
 277    Tasking.Initialize;
 278    System.Soft_Links.Tasking.Init_Tasking_Soft_Links;
 279 end System.Tasking.Protected_Objects;