gcc/ada/a-rttiev.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --          A D A . R E A L _ T I M E . T I M I N G _ E V E N T S           --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --           Copyright (C) 2005-2006, Free Software Foundation, Inc.        --
  10 --                                                                          --
  11 -- GNAT 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 2,  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.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  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 --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 with System.Task_Primitives.Operations;
  35 with System.Tasking.Utilities;
  36 with System.Soft_Links;
  37 --  used for Abort_Defer/Undefer
  38
  39 with Ada.Containers.Doubly_Linked_Lists;
  40 pragma Elaborate_All (Ada.Containers.Doubly_Linked_Lists);
  41
  42 ---------------------------------
  43 -- Ada.Real_Time.Timing_Events --
  44 ---------------------------------
  45
  46 package body Ada.Real_Time.Timing_Events is
  47
  48    use System.Task_Primitives.Operations;
  49    --  for Write_Lock and Unlock
  50
  51    package SSL renames System.Soft_Links;
  52
  53    type Any_Timing_Event is access all Timing_Event'Class;
  54    --  We must also handle user-defined types derived from Timing_Event
  55
  56    ------------
  57    -- Events --
  58    ------------
  59
  60    package Events is new Ada.Containers.Doubly_Linked_Lists (Any_Timing_Event);
  61    --  Provides the type for the container holding pointers to events
  62
  63    All_Events : Events.List;
  64    --  The queue of pending events, ordered by increasing timeout value, that
  65    --  have been "set" by the user via Set_Handler.
  66
  67    Event_Queue_Lock : aliased System.Task_Primitives.RTS_Lock;
  68    --  Used for mutually exclusive access to All_Events
  69
  70    procedure Process_Queued_Events;
  71    --  Examine the queue of pending events for any that have timed-out. For
  72    --  those that have timed-out, remove them from the queue and invoke their
  73    --  handler (unless the user has cancelled the event by setting the handler
  74    --  pointer to null). Mutually exclusive access is held via Event_Queue_Lock
  75    --  during part of the processing.
  76
  77    procedure Insert_Into_Queue (This : Any_Timing_Event);
  78    --  Insert the specified event pointer into the queue of pending events
  79    --  with mutually exclusive access via Event_Queue_Lock.
  80
  81    procedure Remove_From_Queue (This : Any_Timing_Event);
  82    --  Remove the specified event pointer from the queue of pending events
  83    --  with mutually exclusive access via Event_Queue_Lock.
  84    --  This procedure is used by the client-side routines (Set_Handler, etc.).
  85
  86    -----------
  87    -- Timer --
  88    -----------
  89
  90    task Timer is
  91       pragma Priority (System.Priority'Last);
  92       entry Start;
  93    end Timer;
  94
  95    task body Timer is
  96       Period : constant Time_Span := Milliseconds (100);
  97       --  This is a "chiming" clock timer that fires periodically. The period
  98       --  selected is arbitrary and could be changed to suit the application
  99       --  requirements. Obviously a shorter period would give better resolution
 100       --  at the cost of more overhead.
 101    begin
 102       System.Tasking.Utilities.Make_Independent;
 103
 104       --  We await the call to Start to ensure that Event_Queue_Lock has been
 105       --  initialized by the package executable part prior to accessing it in
 106       --  the loop. The task is activated before the first statement of the
 107       --  executable part so it would otherwise be possible for the task to
 108       --  call EnterCriticalSection in Process_Queued_Events before the
 109       --  initialization.
 110
 111       --  We don't simply put the initialization here, prior to the loop,
 112       --  because other application tasks could call the visible routines that
 113       --  also call Enter/LeaveCriticalSection prior to this task doing the
 114       --  initialization.
 115
 116       accept Start;
 117
 118       loop
 119          Process_Queued_Events;
 120          delay until Clock + Period;
 121       end loop;
 122    end Timer;
 123
 124    ---------------------------
 125    -- Process_Queued_Events --
 126    ---------------------------
 127
 128    procedure Process_Queued_Events is
 129       Next_Event : Any_Timing_Event;
 130
 131    begin
 132       loop
 133          SSL.Abort_Defer.all;
 134
 135          Write_Lock (Event_Queue_Lock'Access);
 136
 137          if All_Events.Is_Empty then
 138             Unlock (Event_Queue_Lock'Access);
 139             SSL.Abort_Undefer.all;
 140             return;
 141          else
 142             Next_Event := All_Events.First_Element;
 143          end if;
 144
 145          if Next_Event.Timeout > Clock then
 146
 147             --  We found one that has not yet timed-out. The queue is in
 148             --  ascending order by Timeout so there is no need to continue
 149             --  processing (and indeed we must not continue since we always
 150             --  delete the first element).
 151
 152             Unlock (Event_Queue_Lock'Access);
 153             SSL.Abort_Undefer.all;
 154             return;
 155          end if;
 156
 157          --  We have an event that has timed out so we will process it. It
 158          --  must be the first in the queue so no search is needed.
 159
 160          All_Events.Delete_First;
 161
 162          --  A fundamental issue is that the invocation of the event's handler
 163          --  might call Set_Handler on itself to re-insert itself back into the
 164          --  queue of future events. Thus we cannot hold the lock on the queue
 165          --  while invoking the event's handler.
 166
 167          Unlock (Event_Queue_Lock'Access);
 168
 169          SSL.Abort_Undefer.all;
 170
 171          --  There is no race condition with the user changing the handler
 172          --  pointer while we are processing because we are executing at the
 173          --  highest possible application task priority and are not doing
 174          --  anything to block prior to invoking their handler.
 175
 176          declare
 177             Handler : constant Timing_Event_Handler := Next_Event.Handler;
 178          begin
 179             --  The first act is to clear the event, per D.15 (13/2). Besides,
 180             --  we cannot clear the handler pointer *after* invoking the
 181             --  handler because the handler may have re-inserted the event via
 182             --  Set_Event. Thus we take a copy and then clear the component.
 183
 184             Next_Event.Handler := null;
 185
 186             if Handler /= null then
 187                Handler (Timing_Event (Next_Event.all));
 188             end if;
 189          exception
 190             when others =>
 191                null;
 192          end;
 193       end loop;
 194    end Process_Queued_Events;
 195
 196    -----------------------
 197    -- Insert_Into_Queue --
 198    -----------------------
 199
 200    procedure Insert_Into_Queue (This : Any_Timing_Event) is
 201
 202       function Sooner (Left, Right : Any_Timing_Event) return Boolean;
 203       --  Compares events in terms of timeout values
 204
 205       package By_Timeout is new Events.Generic_Sorting (Sooner);
 206       --  Used to keep the events in ascending order by timeout value
 207
 208       function Sooner (Left, Right : Any_Timing_Event) return Boolean is
 209       begin
 210          return Left.Timeout < Right.Timeout;
 211       end Sooner;
 212
 213    begin
 214       SSL.Abort_Defer.all;
 215
 216       Write_Lock (Event_Queue_Lock'Access);
 217
 218       All_Events.Append (This);
 219
 220       --  A critical property of the implementation of this package is that
 221       --  all occurrences are in ascending order by Timeout. Thus the first
 222       --  event in the queue always has the "next" value for the Timer task
 223       --  to use in its delay statement.
 224
 225       By_Timeout.Sort (All_Events);
 226
 227       Unlock (Event_Queue_Lock'Access);
 228
 229       SSL.Abort_Undefer.all;
 230    end Insert_Into_Queue;
 231
 232    -----------------------
 233    -- Remove_From_Queue --
 234    -----------------------
 235
 236    procedure Remove_From_Queue (This : Any_Timing_Event) is
 237       use Events;
 238       Location : Cursor;
 239    begin
 240       SSL.Abort_Defer.all;
 241
 242       Write_Lock (Event_Queue_Lock'Access);
 243
 244       Location := All_Events.Find (This);
 245       if Location /= No_Element then
 246          All_Events.Delete (Location);
 247       end if;
 248
 249       Unlock (Event_Queue_Lock'Access);
 250
 251       SSL.Abort_Undefer.all;
 252    end Remove_From_Queue;
 253
 254    -----------------
 255    -- Set_Handler --
 256    -----------------
 257
 258    procedure Set_Handler
 259      (Event   : in out Timing_Event;
 260       At_Time : Time;
 261       Handler : Timing_Event_Handler)
 262    is
 263    begin
 264       Remove_From_Queue (Event'Unchecked_Access);
 265       Event.Handler := null;
 266       if At_Time <= Clock then
 267          if Handler /= null then
 268             Handler (Event);
 269          end if;
 270          return;
 271       end if;
 272       if Handler /= null then
 273          Event.Timeout := At_Time;
 274          Event.Handler := Handler;
 275          Insert_Into_Queue (Event'Unchecked_Access);
 276       end if;
 277    end Set_Handler;
 278
 279    -----------------
 280    -- Set_Handler --
 281    -----------------
 282
 283    procedure Set_Handler
 284      (Event   : in out Timing_Event;
 285       In_Time : Time_Span;
 286       Handler : Timing_Event_Handler)
 287    is
 288    begin
 289       Remove_From_Queue (Event'Unchecked_Access);
 290       Event.Handler := null;
 291       if In_Time <= Time_Span_Zero then
 292          if Handler /= null then
 293             Handler (Event);
 294          end if;
 295          return;
 296       end if;
 297       if Handler /= null then
 298          Event.Timeout := Clock + In_Time;
 299          Event.Handler := Handler;
 300          Insert_Into_Queue (Event'Unchecked_Access);
 301       end if;
 302    end Set_Handler;
 303
 304    ---------------------
 305    -- Current_Handler --
 306    ---------------------
 307
 308    function Current_Handler
 309      (Event : Timing_Event) return Timing_Event_Handler
 310    is
 311    begin
 312       return Event.Handler;
 313    end Current_Handler;
 314
 315    --------------------
 316    -- Cancel_Handler --
 317    --------------------
 318
 319    procedure Cancel_Handler
 320      (Event     : in out Timing_Event;
 321       Cancelled : out Boolean)
 322    is
 323    begin
 324       Remove_From_Queue (Event'Unchecked_Access);
 325       Cancelled := Event.Handler /= null;
 326       Event.Handler := null;
 327    end Cancel_Handler;
 328
 329    -------------------
 330    -- Time_Of_Event --
 331    -------------------
 332
 333    function Time_Of_Event (Event : Timing_Event) return Time is
 334    begin
 335       return Event.Timeout;
 336    end Time_Of_Event;
 337
 338    --------------
 339    -- Finalize --
 340    --------------
 341
 342    procedure Finalize (This : in out Timing_Event) is
 343    begin
 344       --  D.15 (19/2) says finalization clears the event
 345
 346       This.Handler := null;
 347       Remove_From_Queue (This'Unchecked_Access);
 348    end Finalize;
 349
 350 begin
 351    Initialize_Lock (Event_Queue_Lock'Access, Level => PO_Level);
 352    Timer.Start;
 353 end Ada.Real_Time.Timing_Events;