gcc/ada/libgnarl/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) 1991-2017, Florida State University             --
  10 --                     Copyright (C) 1995-2017, 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 tasking
  35 --  operations. It causes infinite loops and other problems.
  36
  37 with System.Task_Primitives.Operations;
  38 with System.Soft_Links.Tasking;
  39
  40 with System.Secondary_Stack;
  41 pragma Elaborate_All (System.Secondary_Stack);
  42 pragma Unreferenced (System.Secondary_Stack);
  43 --  Make sure the body of Secondary_Stack is elaborated before calling
  44 --  Init_Tasking_Soft_Links. See comments for this routine for explanation.
  45
  46 package body System.Tasking.Protected_Objects is
  47
  48    use System.Task_Primitives.Operations;
  49
  50    ----------------
  51    -- Local Data --
  52    ----------------
  53
  54    Locking_Policy : Character;
  55    pragma Import (C, Locking_Policy, "__gl_locking_policy");
  56
  57    -------------------------
  58    -- Finalize_Protection --
  59    -------------------------
  60
  61    procedure Finalize_Protection (Object : in out Protection) is
  62    begin
  63       Finalize_Lock (Object.L'Unrestricted_Access);
  64    end Finalize_Protection;
  65
  66    ---------------------------
  67    -- Initialize_Protection --
  68    ---------------------------
  69
  70    procedure Initialize_Protection
  71      (Object           : Protection_Access;
  72       Ceiling_Priority : Integer)
  73    is
  74       Init_Priority : Integer := Ceiling_Priority;
  75
  76    begin
  77       if Init_Priority = Unspecified_Priority then
  78          Init_Priority := System.Priority'Last;
  79       end if;
  80
  81       Initialize_Lock (Init_Priority, Object.L'Access);
  82       Object.Ceiling := System.Any_Priority (Init_Priority);
  83       Object.New_Ceiling := System.Any_Priority (Init_Priority);
  84       Object.Owner := Null_Task;
  85    end Initialize_Protection;
  86
  87    -----------------
  88    -- Get_Ceiling --
  89    -----------------
  90
  91    function Get_Ceiling
  92      (Object : Protection_Access) return System.Any_Priority is
  93    begin
  94       return Object.New_Ceiling;
  95    end Get_Ceiling;
  96
  97    ----------
  98    -- Lock --
  99    ----------
 100
 101    procedure Lock (Object : Protection_Access) is
 102       Ceiling_Violation : Boolean;
 103
 104    begin
 105       --  The lock is made without deferring abort
 106
 107       --  Therefore the abort has to be deferred before calling this routine.
 108       --  This means that the compiler has to generate a Defer_Abort call
 109       --  before the call to Lock.
 110
 111       --  The caller is responsible for undeferring abort, and compiler
 112       --  generated calls must be protected with cleanup handlers to ensure
 113       --  that abort is undeferred in all cases.
 114
 115       --  If pragma Detect_Blocking is active then, as described in the ARM
 116       --  9.5.1, par. 15, we must check whether this is an external call on a
 117       --  protected subprogram with the same target object as that of the
 118       --  protected action that is currently in progress (i.e., if the caller
 119       --  is already the protected object's owner). If this is the case hence
 120       --  Program_Error must be raised.
 121
 122       if Detect_Blocking and then Object.Owner = Self then
 123          raise Program_Error;
 124       end if;
 125
 126       Write_Lock (Object.L'Access, Ceiling_Violation);
 127
 128       if Ceiling_Violation then
 129          raise Program_Error;
 130       end if;
 131
 132       --  We are entering in a protected action, so that we increase the
 133       --  protected object nesting level (if pragma Detect_Blocking is
 134       --  active), and update the protected object's owner.
 135
 136       if Detect_Blocking then
 137          declare
 138             Self_Id : constant Task_Id := Self;
 139          begin
 140             --  Update the protected object's owner
 141
 142             Object.Owner := Self_Id;
 143
 144             --  Increase protected object nesting level
 145
 146             Self_Id.Common.Protected_Action_Nesting :=
 147               Self_Id.Common.Protected_Action_Nesting + 1;
 148          end;
 149       end if;
 150    end Lock;
 151
 152    --------------------
 153    -- Lock_Read_Only --
 154    --------------------
 155
 156    procedure Lock_Read_Only (Object : Protection_Access) is
 157       Ceiling_Violation : Boolean;
 158
 159    begin
 160       --  If pragma Detect_Blocking is active then, as described in the ARM
 161       --  9.5.1, par. 15, we must check whether this is an external call on
 162       --  protected subprogram with the same target object as that of the
 163       --  protected action that is currently in progress (i.e., if the caller
 164       --  is already the protected object's owner). If this is the case hence
 165       --  Program_Error must be raised.
 166       --
 167       --  Note that in this case (getting read access), several tasks may have
 168       --  read ownership of the protected object, so that this method of
 169       --  storing the (single) protected object's owner does not work reliably
 170       --  for read locks. However, this is the approach taken for two major
 171       --  reasons: first, this function is not currently being used (it is
 172       --  provided for possible future use), and second, it largely simplifies
 173       --  the implementation.
 174
 175       if Detect_Blocking and then Object.Owner = Self then
 176          raise Program_Error;
 177       end if;
 178
 179       Read_Lock (Object.L'Access, Ceiling_Violation);
 180
 181       if Ceiling_Violation then
 182          raise Program_Error;
 183       end if;
 184
 185       --  We are entering in a protected action, so we increase the protected
 186       --  object nesting level (if pragma Detect_Blocking is active).
 187
 188       if Detect_Blocking then
 189          declare
 190             Self_Id : constant Task_Id := Self;
 191          begin
 192             --  Update the protected object's owner
 193
 194             Object.Owner := Self_Id;
 195
 196             --  Increase protected object nesting level
 197
 198             Self_Id.Common.Protected_Action_Nesting :=
 199               Self_Id.Common.Protected_Action_Nesting + 1;
 200          end;
 201       end if;
 202    end Lock_Read_Only;
 203
 204    -----------------
 205    -- Set_Ceiling --
 206    -----------------
 207
 208    procedure Set_Ceiling
 209      (Object : Protection_Access;
 210       Prio   : System.Any_Priority) is
 211    begin
 212       Object.New_Ceiling := Prio;
 213    end Set_Ceiling;
 214
 215    ------------
 216    -- Unlock --
 217    ------------
 218
 219    procedure Unlock (Object : Protection_Access) is
 220    begin
 221       --  We are exiting from a protected action, so that we decrease the
 222       --  protected object nesting level (if pragma Detect_Blocking is
 223       --  active), and remove ownership of the protected object.
 224
 225       if Detect_Blocking then
 226          declare
 227             Self_Id : constant Task_Id := Self;
 228
 229          begin
 230             --  Calls to this procedure can only take place when being within
 231             --  a protected action and when the caller is the protected
 232             --  object's owner.
 233
 234             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 235                              and then Object.Owner = Self_Id);
 236
 237             --  Remove ownership of the protected object
 238
 239             Object.Owner := Null_Task;
 240
 241             --  We are exiting from a protected action, so we decrease the
 242             --  protected object nesting level.
 243
 244             Self_Id.Common.Protected_Action_Nesting :=
 245               Self_Id.Common.Protected_Action_Nesting - 1;
 246          end;
 247       end if;
 248
 249       --  Before releasing the mutex we must actually update its ceiling
 250       --  priority if it has been changed.
 251
 252       if Object.New_Ceiling /= Object.Ceiling then
 253          if Locking_Policy = 'C' then
 254             System.Task_Primitives.Operations.Set_Ceiling
 255               (Object.L'Access, Object.New_Ceiling);
 256          end if;
 257
 258          Object.Ceiling := Object.New_Ceiling;
 259       end if;
 260
 261       Unlock (Object.L'Access);
 262
 263    end Unlock;
 264
 265 begin
 266    --  Ensure that tasking is initialized, as well as tasking soft links
 267    --  when using protected objects.
 268
 269    Tasking.Initialize;
 270    System.Soft_Links.Tasking.Init_Tasking_Soft_Links;
 271 end System.Tasking.Protected_Objects;