gcc/ada/s-taasde.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
   4 --                                                                          --
   5 --           S Y S T E M . T A S K I N G . A S Y N C _ D E L A Y S          --
   6 --                                                                          --
   7 --                                  B o d y                                 --
   8 --                                                                          --
   9 --         Copyright (C) 1998-2004, Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- GNARL 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. GNARL 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 GNARL; see file COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, 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 -- 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 pragma Polling (Off);
  35 --  Turn off polling, we do not want ATC polling to take place during
  36 --  tasking operations. It causes infinite loops and other problems.
  37
  38 with Ada.Exceptions;
  39 --  Used for Raise_Exception
  40
  41 with System.Task_Primitives.Operations;
  42 --  Used for Write_Lock,
  43 --           Unlock,
  44 --           Self,
  45 --           Monotonic_Clock,
  46 --           Self,
  47 --           Timed_Sleep,
  48 --           Wakeup,
  49 --           Yield
  50
  51 with System.Tasking.Utilities;
  52 --  Used for Make_Independent
  53
  54 with System.Tasking.Initialization;
  55 --  Used for Defer_Abort
  56 --           Undefer_Abort
  57
  58 with System.Tasking.Debug;
  59 --  Used for Trace
  60
  61 with System.OS_Primitives;
  62 --  used for Max_Sensible_Delay
  63
  64 with Ada.Task_Identification;
  65 --  used for Task_Id type
  66
  67 with System.Parameters;
  68 --  used for Single_Lock
  69 --           Runtime_Traces
  70
  71 with System.Traces.Tasking;
  72 --  used for Send_Trace_Info
  73
  74 with Unchecked_Conversion;
  75
  76 package body System.Tasking.Async_Delays is
  77
  78    package STPO renames System.Task_Primitives.Operations;
  79    package ST renames System.Tasking;
  80    package STU renames System.Tasking.Utilities;
  81    package STI renames System.Tasking.Initialization;
  82    package OSP renames System.OS_Primitives;
  83
  84    use Parameters;
  85    use System.Traces;
  86    use System.Traces.Tasking;
  87
  88    function To_System is new Unchecked_Conversion
  89      (Ada.Task_Identification.Task_Id, Task_Id);
  90
  91    Timer_Server_ID : ST.Task_Id;
  92
  93    Timer_Attention : Boolean := False;
  94    pragma Atomic (Timer_Attention);
  95
  96    task Timer_Server is
  97       pragma Interrupt_Priority (System.Any_Priority'Last);
  98    end Timer_Server;
  99
 100    --  The timer queue is a circular doubly linked list, ordered by absolute
 101    --  wakeup time. The first item in the queue is Timer_Queue.Succ.
 102    --  It is given a Resume_Time that is larger than any legitimate wakeup
 103    --  time, so that the ordered insertion will always stop searching when it
 104    --  gets back to the queue header block.
 105
 106    Timer_Queue : aliased Delay_Block;
 107
 108    ------------------------
 109    -- Cancel_Async_Delay --
 110    ------------------------
 111
 112    --  This should (only) be called from the compiler-generated cleanup routine
 113    --  for an async. select statement with delay statement as trigger. The
 114    --  effect should be to remove the delay from the timer queue, and exit one
 115    --  ATC nesting level.
 116    --  The usage and logic are similar to Cancel_Protected_Entry_Call, but
 117    --  simplified because this is not a true entry call.
 118
 119    procedure Cancel_Async_Delay (D : Delay_Block_Access) is
 120       Dpred : Delay_Block_Access;
 121       Dsucc : Delay_Block_Access;
 122
 123    begin
 124       --  Note that we mark the delay as being cancelled
 125       --  using a level value that is reserved.
 126
 127       --  make this operation idempotent
 128
 129       if D.Level = ATC_Level_Infinity then
 130          return;
 131       end if;
 132
 133       D.Level := ATC_Level_Infinity;
 134
 135       --  remove self from timer queue
 136
 137       STI.Defer_Abort_Nestable (D.Self_Id);
 138
 139       if Single_Lock then
 140          STPO.Lock_RTS;
 141       end if;
 142
 143       STPO.Write_Lock (Timer_Server_ID);
 144       Dpred := D.Pred;
 145       Dsucc := D.Succ;
 146       Dpred.Succ := Dsucc;
 147       Dsucc.Pred := Dpred;
 148       D.Succ := D;
 149       D.Pred := D;
 150       STPO.Unlock (Timer_Server_ID);
 151
 152       --  Note that the above deletion code is required to be
 153       --  idempotent, since the block may have been dequeued
 154       --  previously by the Timer_Server.
 155
 156       --  leave the asynchronous select
 157
 158       STPO.Write_Lock (D.Self_Id);
 159       STU.Exit_One_ATC_Level (D.Self_Id);
 160       STPO.Unlock (D.Self_Id);
 161
 162       if Single_Lock then
 163          STPO.Unlock_RTS;
 164       end if;
 165
 166       STI.Undefer_Abort_Nestable (D.Self_Id);
 167    end Cancel_Async_Delay;
 168
 169    ---------------------------
 170    -- Enqueue_Time_Duration --
 171    ---------------------------
 172
 173    function Enqueue_Duration
 174      (T    : in Duration;
 175       D    : Delay_Block_Access)
 176       return Boolean
 177    is
 178    begin
 179       if T <= 0.0 then
 180          D.Timed_Out := True;
 181          STPO.Yield;
 182          return False;
 183
 184       else
 185          --  The corresponding call to Undefer_Abort is performed by the
 186          --  expanded code (see exp_ch9).
 187
 188          STI.Defer_Abort (STPO.Self);
 189          Time_Enqueue
 190            (STPO.Monotonic_Clock
 191             + Duration'Min (T, OSP.Max_Sensible_Delay), D);
 192          return True;
 193       end if;
 194    end Enqueue_Duration;
 195
 196    ------------------
 197    -- Time_Enqueue --
 198    ------------------
 199
 200    --  Allocate a queue element for the wakeup time T and put it in the
 201    --  queue in wakeup time order.  Assume we are on an asynchronous
 202    --  select statement with delay trigger.  Put the calling task to
 203    --  sleep until either the delay expires or is cancelled.
 204
 205    --  We use one entry call record for this delay, since we have
 206    --  to increment the ATC nesting level, but since it is not a
 207    --  real entry call we do not need to use any of the fields of
 208    --  the call record.  The following code implements a subset of
 209    --  the actions for the asynchronous case of Protected_Entry_Call,
 210    --  much simplified since we know this never blocks, and does not
 211    --  have the full semantics of a protected entry call.
 212
 213    procedure Time_Enqueue
 214      (T : Duration;
 215       D : Delay_Block_Access)
 216    is
 217       Self_Id : constant Task_Id  := STPO.Self;
 218       Q       : Delay_Block_Access;
 219
 220       use type ST.Task_Id;
 221       --  for visibility of operator "="
 222
 223    begin
 224       pragma Debug (Debug.Trace (Self_Id, "Async_Delay", 'P'));
 225       pragma Assert (Self_Id.Deferral_Level = 1,
 226         "async delay from within abort-deferred region");
 227
 228       if Self_Id.ATC_Nesting_Level = ATC_Level'Last then
 229          Ada.Exceptions.Raise_Exception (Storage_Error'Identity,
 230            "not enough ATC nesting levels");
 231       end if;
 232
 233       Self_Id.ATC_Nesting_Level := Self_Id.ATC_Nesting_Level + 1;
 234
 235       pragma Debug
 236         (Debug.Trace (Self_Id, "ASD: entered ATC level: " &
 237          ATC_Level'Image (Self_Id.ATC_Nesting_Level), 'A'));
 238
 239       D.Level := Self_Id.ATC_Nesting_Level;
 240       D.Self_Id := Self_Id;
 241       D.Resume_Time := T;
 242
 243       if Single_Lock then
 244          STPO.Lock_RTS;
 245       end if;
 246
 247       STPO.Write_Lock (Timer_Server_ID);
 248
 249       --  Previously, there was code here to dynamically create
 250       --  the Timer_Server task, if one did not already exist.
 251       --  That code had a timing window that could allow multiple
 252       --  timer servers to be created. Luckily, the need for
 253       --  postponing creation of the timer server should now be
 254       --  gone, since this package will only be linked in if
 255       --  there are calls to enqueue calls on the timer server.
 256
 257       --  Insert D in the timer queue, at the position determined
 258       --  by the wakeup time T.
 259
 260       Q := Timer_Queue.Succ;
 261
 262       while Q.Resume_Time < T loop
 263          Q := Q.Succ;
 264       end loop;
 265
 266       --  Q is the block that has Resume_Time equal to or greater than
 267       --  T. After the insertion we want Q to be the successor of D.
 268
 269       D.Succ := Q;
 270       D.Pred := Q.Pred;
 271       D.Pred.Succ := D;
 272       Q.Pred := D;
 273
 274       --  If the new element became the head of the queue,
 275       --  signal the Timer_Server to wake up.
 276
 277       if Timer_Queue.Succ = D then
 278          Timer_Attention := True;
 279          STPO.Wakeup (Timer_Server_ID, ST.Timer_Server_Sleep);
 280       end if;
 281
 282       STPO.Unlock (Timer_Server_ID);
 283
 284       if Single_Lock then
 285          STPO.Unlock_RTS;
 286       end if;
 287    end Time_Enqueue;
 288
 289    ---------------
 290    -- Timed_Out --
 291    ---------------
 292
 293    function Timed_Out (D : Delay_Block_Access) return Boolean is
 294    begin
 295       return D.Timed_Out;
 296    end Timed_Out;
 297
 298    ------------------
 299    -- Timer_Server --
 300    ------------------
 301
 302    task body Timer_Server is
 303       function Get_Next_Wakeup_Time return Duration;
 304       --  Used to initialize Next_Wakeup_Time, but also to ensure that
 305       --  Make_Independent is called during the elaboration of this task
 306
 307       --------------------------
 308       -- Get_Next_Wakeup_Time --
 309       --------------------------
 310
 311       function Get_Next_Wakeup_Time return Duration is
 312       begin
 313          STU.Make_Independent;
 314          return Duration'Last;
 315       end Get_Next_Wakeup_Time;
 316
 317       Next_Wakeup_Time : Duration := Get_Next_Wakeup_Time;
 318       Timedout         : Boolean;
 319       Yielded          : Boolean;
 320       Now              : Duration;
 321       Dequeued         : Delay_Block_Access;
 322       Dequeued_Task    : Task_Id;
 323
 324    begin
 325       Timer_Server_ID := STPO.Self;
 326
 327       --  Initialize the timer queue to empty, and make the wakeup time of the
 328       --  header node be larger than any real wakeup time we will ever use.
 329
 330       loop
 331          STI.Defer_Abort (Timer_Server_ID);
 332
 333          if Single_Lock then
 334             STPO.Lock_RTS;
 335          end if;
 336
 337          STPO.Write_Lock (Timer_Server_ID);
 338
 339          --  The timer server needs to catch pending aborts after finalization
 340          --  of library packages. If it doesn't poll for it, the server will
 341          --  sometimes hang.
 342
 343          if not Timer_Attention then
 344             Timer_Server_ID.Common.State := ST.Timer_Server_Sleep;
 345
 346             if Next_Wakeup_Time = Duration'Last then
 347                Timer_Server_ID.User_State := 1;
 348                Next_Wakeup_Time :=
 349                  STPO.Monotonic_Clock + OSP.Max_Sensible_Delay;
 350
 351             else
 352                Timer_Server_ID.User_State := 2;
 353             end if;
 354
 355             STPO.Timed_Sleep
 356               (Timer_Server_ID, Next_Wakeup_Time,
 357                OSP.Absolute_RT, ST.Timer_Server_Sleep,
 358                Timedout, Yielded);
 359             Timer_Server_ID.Common.State := ST.Runnable;
 360          end if;
 361
 362          --  Service all of the wakeup requests on the queue whose times have
 363          --  been reached, and update Next_Wakeup_Time to next wakeup time
 364          --  after that (the wakeup time of the head of the queue if any, else
 365          --  a time far in the future).
 366
 367          Timer_Server_ID.User_State := 3;
 368          Timer_Attention := False;
 369
 370          Now := STPO.Monotonic_Clock;
 371
 372          while Timer_Queue.Succ.Resume_Time <= Now loop
 373
 374             --  Dequeue the waiting task from the front of the queue.
 375
 376             pragma Debug (System.Tasking.Debug.Trace
 377               (Timer_Server_ID, "Timer service: waking up waiting task", 'E'));
 378
 379             Dequeued := Timer_Queue.Succ;
 380             Timer_Queue.Succ := Dequeued.Succ;
 381             Dequeued.Succ.Pred := Dequeued.Pred;
 382             Dequeued.Succ := Dequeued;
 383             Dequeued.Pred := Dequeued;
 384
 385             --  We want to abort the queued task to the level of the async.
 386             --  select statement with the delay. To do that, we need to lock
 387             --  the ATCB of that task, but to avoid deadlock we need to release
 388             --  the lock of the Timer_Server. This leaves a window in which
 389             --  another task might perform an enqueue or dequeue operation on
 390             --  the timer queue, but that is OK because we always restart the
 391             --  next iteration at the head of the queue.
 392
 393             if Parameters.Runtime_Traces then
 394                Send_Trace_Info (E_Kill, Dequeued.Self_Id);
 395             end if;
 396
 397             STPO.Unlock (Timer_Server_ID);
 398             STPO.Write_Lock (Dequeued.Self_Id);
 399             Dequeued_Task := Dequeued.Self_Id;
 400             Dequeued.Timed_Out := True;
 401             STI.Locked_Abort_To_Level
 402               (Timer_Server_ID, Dequeued_Task, Dequeued.Level - 1);
 403             STPO.Unlock (Dequeued_Task);
 404             STPO.Write_Lock (Timer_Server_ID);
 405          end loop;
 406
 407          Next_Wakeup_Time := Timer_Queue.Succ.Resume_Time;
 408
 409          --  Service returns the Next_Wakeup_Time.
 410          --  The Next_Wakeup_Time is either an infinity (no delay request)
 411          --  or the wakeup time of the queue head. This value is used for
 412          --  an actual delay in this server.
 413
 414          STPO.Unlock (Timer_Server_ID);
 415
 416          if Single_Lock then
 417             STPO.Unlock_RTS;
 418          end if;
 419
 420          STI.Undefer_Abort (Timer_Server_ID);
 421       end loop;
 422    end Timer_Server;
 423
 424    ------------------------------
 425    -- Package Body Elaboration --
 426    ------------------------------
 427
 428 begin
 429    Timer_Queue.Succ := Timer_Queue'Unchecked_Access;
 430    Timer_Queue.Pred := Timer_Queue'Unchecked_Access;
 431    Timer_Queue.Resume_Time := Duration'Last;
 432    Timer_Server_ID := To_System (Timer_Server'Identity);
 433 end System.Tasking.Async_Delays;