gcc/ada/s-tposen.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 --                          S I N G L E _ E N T R Y                         --
   7 --                                                                          --
   8 --                                B o d y                                   --
   9 --                                                                          --
  10 --         Copyright (C) 1998-2007, Free Software Foundation, Inc.          --
  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 Style_Checks (All_Checks);
  36 --  Turn off subprogram ordering check, since restricted GNARLI
  37 --  subprograms are gathered together at end.
  38
  39 --  This package provides an optimized version of Protected_Objects.Operations
  40 --  and Protected_Objects.Entries making the following assumptions:
  41
  42 --    PO has only one entry
  43 --    There is only one caller at a time (No_Entry_Queue)
  44 --    There is no dynamic priority support (No_Dynamic_Priorities)
  45 --    No Abort Statements
  46 --     (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)
  47 --    PO are at library level
  48 --    No Requeue
  49 --    None of the tasks will terminate (no need for finalization)
  50
  51 --  This interface is intended to be used in the ravenscar and restricted
  52 --  profiles, the compiler is responsible for ensuring that the conditions
  53 --  mentioned above are respected, except for the No_Entry_Queue restriction
  54 --  that is checked dynamically in this package, since the check cannot be
  55 --  performed at compile time, and is relatively cheap (see PO_Do_Or_Queue,
  56 --  Service_Entry).
  57
  58 pragma Polling (Off);
  59 --  Turn off polling, we do not want polling to take place during tasking
  60 --  operations. It can cause  infinite loops and other problems.
  61
  62 pragma Suppress (All_Checks);
  63
  64 with System.Task_Primitives.Operations;
  65 --  used for Self
  66 --           Finalize_Lock
  67 --           Write_Lock
  68 --           Unlock
  69
  70 with Ada.Exceptions;
  71 --  used for Exception_Id
  72 --           Raise_Exception
  73
  74 with System.Parameters;
  75 --  used for Single_Lock
  76
  77 package body System.Tasking.Protected_Objects.Single_Entry is
  78
  79    package STPO renames System.Task_Primitives.Operations;
  80
  81    use Parameters;
  82
  83    -----------------------
  84    -- Local Subprograms --
  85    -----------------------
  86
  87    procedure Send_Program_Error
  88      (Self_Id    : Task_Id;
  89       Entry_Call : Entry_Call_Link);
  90    pragma Inline (Send_Program_Error);
  91    --  Raise Program_Error in the caller of the specified entry call
  92
  93    --------------------------
  94    -- Entry Calls Handling --
  95    --------------------------
  96
  97    procedure Wakeup_Entry_Caller
  98      (Self_ID    : Task_Id;
  99       Entry_Call : Entry_Call_Link;
 100       New_State  : Entry_Call_State);
 101    pragma Inline (Wakeup_Entry_Caller);
 102    --  This is called at the end of service of an entry call,
 103    --  to abort the caller if he is in an abortable part, and
 104    --  to wake up the caller if he is on Entry_Caller_Sleep.
 105    --  Call it holding the lock of Entry_Call.Self.
 106    --
 107    --  Timed_Call or Simple_Call:
 108    --    The caller is waiting on Entry_Caller_Sleep, in
 109    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 110
 111    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link);
 112    pragma Inline (Wait_For_Completion);
 113    --  This procedure suspends the calling task until the specified entry call
 114    --  has either been completed or cancelled. On exit, the call will not be
 115    --  queued. This waits for calls on protected entries.
 116    --  Call this only when holding Self_ID locked.
 117
 118    procedure Wait_For_Completion_With_Timeout
 119      (Entry_Call  : Entry_Call_Link;
 120       Wakeup_Time : Duration;
 121       Mode        : Delay_Modes);
 122    --  Same as Wait_For_Completion but it waits for a timeout with the value
 123    --  specified in Wakeup_Time as well.
 124
 125    procedure Check_Exception
 126      (Self_ID : Task_Id;
 127       Entry_Call : Entry_Call_Link);
 128    pragma Inline (Check_Exception);
 129    --  Raise any pending exception from the Entry_Call.
 130    --  This should be called at the end of every compiler interface procedure
 131    --  that implements an entry call.
 132    --  The caller should not be holding any locks, or there will be deadlock.
 133
 134    procedure PO_Do_Or_Queue
 135      (Self_Id    : Task_Id;
 136       Object     : Protection_Entry_Access;
 137       Entry_Call : Entry_Call_Link);
 138    --  This procedure executes or queues an entry call, depending
 139    --  on the status of the corresponding barrier. It assumes that the
 140    --  specified object is locked.
 141
 142    ---------------------
 143    -- Check_Exception --
 144    ---------------------
 145
 146    procedure Check_Exception
 147      (Self_ID    : Task_Id;
 148       Entry_Call : Entry_Call_Link)
 149    is
 150       pragma Warnings (Off, Self_ID);
 151
 152       procedure Internal_Raise (X : Ada.Exceptions.Exception_Id);
 153       pragma Import (C, Internal_Raise, "__gnat_raise_with_msg");
 154
 155       use type Ada.Exceptions.Exception_Id;
 156
 157       E : constant Ada.Exceptions.Exception_Id :=
 158         Entry_Call.Exception_To_Raise;
 159
 160    begin
 161       if E /= Ada.Exceptions.Null_Id then
 162          Internal_Raise (E);
 163       end if;
 164    end Check_Exception;
 165
 166    ------------------------
 167    -- Send_Program_Error --
 168    ------------------------
 169
 170    procedure Send_Program_Error
 171      (Self_Id    : Task_Id;
 172       Entry_Call : Entry_Call_Link)
 173    is
 174       Caller : constant Task_Id := Entry_Call.Self;
 175    begin
 176       Entry_Call.Exception_To_Raise := Program_Error'Identity;
 177
 178       if Single_Lock then
 179          STPO.Lock_RTS;
 180       end if;
 181
 182       STPO.Write_Lock (Caller);
 183       Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 184       STPO.Unlock (Caller);
 185
 186       if Single_Lock then
 187          STPO.Unlock_RTS;
 188       end if;
 189    end Send_Program_Error;
 190
 191    -------------------------
 192    -- Wait_For_Completion --
 193    -------------------------
 194
 195    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is
 196       Self_Id : constant Task_Id := Entry_Call.Self;
 197    begin
 198       Self_Id.Common.State := Entry_Caller_Sleep;
 199       STPO.Sleep (Self_Id, Entry_Caller_Sleep);
 200       Self_Id.Common.State := Runnable;
 201    end Wait_For_Completion;
 202
 203    --------------------------------------
 204    -- Wait_For_Completion_With_Timeout --
 205    --------------------------------------
 206
 207    procedure Wait_For_Completion_With_Timeout
 208      (Entry_Call  : Entry_Call_Link;
 209       Wakeup_Time : Duration;
 210       Mode        : Delay_Modes)
 211    is
 212       Self_Id  : constant Task_Id := Entry_Call.Self;
 213       Timedout : Boolean;
 214
 215       Yielded  : Boolean;
 216       pragma Unreferenced (Yielded);
 217
 218       use type Ada.Exceptions.Exception_Id;
 219
 220    begin
 221       --  This procedure waits for the entry call to be served, with a timeout.
 222       --  It tries to cancel the call if the timeout expires before the call is
 223       --  served.
 224
 225       --  If we wake up from the timed sleep operation here, it may be for the
 226       --  following possible reasons:
 227
 228       --  1) The entry call is done being served.
 229       --  2) The timeout has expired (Timedout = True)
 230
 231       --  Once the timeout has expired we may need to continue to wait if the
 232       --  call is already being serviced. In that case, we want to go back to
 233       --  sleep, but without any timeout. The variable Timedout is used to
 234       --  control this. If the Timedout flag is set, we do not need to Sleep
 235       --  with a timeout. We just sleep until we get a wakeup for some status
 236       --  change.
 237
 238       pragma Assert (Entry_Call.Mode = Timed_Call);
 239       Self_Id.Common.State := Entry_Caller_Sleep;
 240
 241       STPO.Timed_Sleep
 242         (Self_Id, Wakeup_Time, Mode, Entry_Caller_Sleep, Timedout, Yielded);
 243
 244       if Timedout then
 245          Entry_Call.State := Cancelled;
 246       else
 247          Entry_Call.State := Done;
 248       end if;
 249
 250       Self_Id.Common.State := Runnable;
 251    end Wait_For_Completion_With_Timeout;
 252
 253    -------------------------
 254    -- Wakeup_Entry_Caller --
 255    -------------------------
 256
 257    --  This is called at the end of service of an entry call, to abort the
 258    --  caller if he is in an abortable part, and to wake up the caller if it
 259    --  is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
 260
 261    --  (This enforces the rule that a task must be off-queue if its state is
 262    --  Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
 263
 264    --  Timed_Call or Simple_Call:
 265    --    The caller is waiting on Entry_Caller_Sleep, in
 266    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 267
 268    --  Conditional_Call:
 269    --    The caller might be in Wait_For_Completion,
 270    --    waiting for a rendezvous (possibly requeued without abort)
 271    --    to complete.
 272
 273    procedure Wakeup_Entry_Caller
 274      (Self_ID    : Task_Id;
 275       Entry_Call : Entry_Call_Link;
 276       New_State  : Entry_Call_State)
 277    is
 278       pragma Warnings (Off, Self_ID);
 279
 280       Caller : constant Task_Id := Entry_Call.Self;
 281
 282    begin
 283       pragma Assert (New_State = Done or else New_State = Cancelled);
 284       pragma Assert
 285         (Caller.Common.State /= Terminated and then
 286          Caller.Common.State /= Unactivated);
 287
 288       Entry_Call.State := New_State;
 289       STPO.Wakeup (Caller, Entry_Caller_Sleep);
 290    end Wakeup_Entry_Caller;
 291
 292    -----------------------
 293    -- Restricted GNARLI --
 294    -----------------------
 295
 296    --------------------------------
 297    -- Complete_Single_Entry_Body --
 298    --------------------------------
 299
 300    procedure Complete_Single_Entry_Body (Object : Protection_Entry_Access) is
 301       pragma Warnings (Off, Object);
 302
 303    begin
 304       --  Nothing needs to do (Object.Call_In_Progress.Exception_To_Raise
 305       --  has already been set to Null_Id).
 306
 307       null;
 308    end Complete_Single_Entry_Body;
 309
 310    --------------------------------------------
 311    -- Exceptional_Complete_Single_Entry_Body --
 312    --------------------------------------------
 313
 314    procedure Exceptional_Complete_Single_Entry_Body
 315      (Object : Protection_Entry_Access;
 316       Ex     : Ada.Exceptions.Exception_Id) is
 317    begin
 318       Object.Call_In_Progress.Exception_To_Raise := Ex;
 319    end Exceptional_Complete_Single_Entry_Body;
 320
 321    ---------------------------------
 322    -- Initialize_Protection_Entry --
 323    ---------------------------------
 324
 325    procedure Initialize_Protection_Entry
 326      (Object            : Protection_Entry_Access;
 327       Ceiling_Priority  : Integer;
 328       Compiler_Info     : System.Address;
 329       Entry_Body        : Entry_Body_Access)
 330    is
 331       Init_Priority : Integer := Ceiling_Priority;
 332    begin
 333       if Init_Priority = Unspecified_Priority then
 334          Init_Priority := System.Priority'Last;
 335       end if;
 336
 337       STPO.Initialize_Lock (Init_Priority, Object.L'Access);
 338       Object.Ceiling := System.Any_Priority (Init_Priority);
 339       Object.Owner := Null_Task;
 340       Object.Compiler_Info := Compiler_Info;
 341       Object.Call_In_Progress := null;
 342       Object.Entry_Body := Entry_Body;
 343       Object.Entry_Queue := null;
 344    end Initialize_Protection_Entry;
 345
 346    ----------------
 347    -- Lock_Entry --
 348    ----------------
 349
 350    --  Compiler interface only.
 351    --  Do not call this procedure from within the run-time system.
 352
 353    procedure Lock_Entry (Object : Protection_Entry_Access) is
 354       Ceiling_Violation : Boolean;
 355
 356    begin
 357       --  If pragma Detect_Blocking is active then, as described in the ARM
 358       --  9.5.1, par. 15, we must check whether this is an external call on a
 359       --  protected subprogram with the same target object as that of the
 360       --  protected action that is currently in progress (i.e., if the caller
 361       --  is already the protected object's owner). If this is the case hence
 362       --  Program_Error must be raised.
 363
 364       if Detect_Blocking and then Object.Owner = Self then
 365          raise Program_Error;
 366       end if;
 367
 368       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 369
 370       if Ceiling_Violation then
 371          raise Program_Error;
 372       end if;
 373
 374       --  We are entering in a protected action, so that we increase the
 375       --  protected object nesting level (if pragma Detect_Blocking is
 376       --  active), and update the protected object's owner.
 377
 378       if Detect_Blocking then
 379          declare
 380             Self_Id : constant Task_Id := Self;
 381
 382          begin
 383             --  Update the protected object's owner
 384
 385             Object.Owner := Self_Id;
 386
 387             --  Increase protected object nesting level
 388
 389             Self_Id.Common.Protected_Action_Nesting :=
 390               Self_Id.Common.Protected_Action_Nesting + 1;
 391          end;
 392       end if;
 393    end Lock_Entry;
 394
 395    --------------------------
 396    -- Lock_Read_Only_Entry --
 397    --------------------------
 398
 399    --  Compiler interface only
 400
 401    --  Do not call this procedure from within the runtime system
 402
 403    procedure Lock_Read_Only_Entry (Object : Protection_Entry_Access) is
 404       Ceiling_Violation : Boolean;
 405
 406    begin
 407       --  If pragma Detect_Blocking is active then, as described in the ARM
 408       --  9.5.1, par. 15, we must check whether this is an external call on a
 409       --  protected subprogram with the same target object as that of the
 410       --  protected action that is currently in progress (i.e., if the caller
 411       --  is already the protected object's owner). If this is the case hence
 412       --  Program_Error must be raised.
 413
 414       --  Note that in this case (getting read access), several tasks may
 415       --  have read ownership of the protected object, so that this method of
 416       --  storing the (single) protected object's owner does not work
 417       --  reliably for read locks. However, this is the approach taken for two
 418       --  major reasosn: first, this function is not currently being used (it
 419       --  is provided for possible future use), and second, it largely
 420       --  simplifies the implementation.
 421
 422       if Detect_Blocking and then Object.Owner = Self then
 423          raise Program_Error;
 424       end if;
 425
 426       STPO.Read_Lock (Object.L'Access, Ceiling_Violation);
 427
 428       if Ceiling_Violation then
 429          raise Program_Error;
 430       end if;
 431
 432       --  We are entering in a protected action, so that we increase the
 433       --  protected object nesting level (if pragma Detect_Blocking is
 434       --  active), and update the protected object's owner.
 435
 436       if Detect_Blocking then
 437          declare
 438             Self_Id : constant Task_Id := Self;
 439
 440          begin
 441             --  Update the protected object's owner
 442
 443             Object.Owner := Self_Id;
 444
 445             --  Increase protected object nesting level
 446
 447             Self_Id.Common.Protected_Action_Nesting :=
 448               Self_Id.Common.Protected_Action_Nesting + 1;
 449          end;
 450       end if;
 451    end Lock_Read_Only_Entry;
 452
 453    --------------------
 454    -- PO_Do_Or_Queue --
 455    --------------------
 456
 457    procedure PO_Do_Or_Queue
 458      (Self_Id    : Task_Id;
 459       Object     : Protection_Entry_Access;
 460       Entry_Call : Entry_Call_Link)
 461    is
 462       Barrier_Value : Boolean;
 463
 464    begin
 465       --  When the Action procedure for an entry body returns, it must be
 466       --  completed (having called [Exceptional_]Complete_Entry_Body).
 467
 468       Barrier_Value := Object.Entry_Body.Barrier (Object.Compiler_Info, 1);
 469
 470       if Barrier_Value then
 471          if Object.Call_In_Progress /= null then
 472
 473             --  This violates the No_Entry_Queue restriction, send
 474             --  Program_Error to the caller.
 475
 476             Send_Program_Error (Self_Id, Entry_Call);
 477             return;
 478          end if;
 479
 480          Object.Call_In_Progress := Entry_Call;
 481          Object.Entry_Body.Action
 482            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 483          Object.Call_In_Progress := null;
 484
 485          if Single_Lock then
 486             STPO.Lock_RTS;
 487          end if;
 488
 489          STPO.Write_Lock (Entry_Call.Self);
 490          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 491          STPO.Unlock (Entry_Call.Self);
 492
 493          if Single_Lock then
 494             STPO.Unlock_RTS;
 495          end if;
 496
 497       elsif Entry_Call.Mode /= Conditional_Call then
 498          if Object.Entry_Queue /= null then
 499
 500             --  This violates the No_Entry_Queue restriction, send
 501             --  Program_Error to the caller.
 502
 503             Send_Program_Error (Self_Id, Entry_Call);
 504             return;
 505          else
 506             Object.Entry_Queue := Entry_Call;
 507          end if;
 508
 509       else
 510          --  Conditional_Call
 511
 512          if Single_Lock then
 513             STPO.Lock_RTS;
 514          end if;
 515
 516          STPO.Write_Lock (Entry_Call.Self);
 517          Wakeup_Entry_Caller (Self_Id, Entry_Call, Cancelled);
 518          STPO.Unlock (Entry_Call.Self);
 519
 520          if Single_Lock then
 521             STPO.Unlock_RTS;
 522          end if;
 523       end if;
 524
 525    exception
 526       when others =>
 527          Send_Program_Error
 528            (Self_Id, Entry_Call);
 529    end PO_Do_Or_Queue;
 530
 531    ----------------------------
 532    -- Protected_Single_Count --
 533    ----------------------------
 534
 535    function Protected_Count_Entry (Object : Protection_Entry) return Natural is
 536    begin
 537       if Object.Entry_Queue /= null then
 538          return 1;
 539       else
 540          return 0;
 541       end if;
 542    end Protected_Count_Entry;
 543
 544    ---------------------------------
 545    -- Protected_Single_Entry_Call --
 546    ---------------------------------
 547
 548    procedure Protected_Single_Entry_Call
 549      (Object             : Protection_Entry_Access;
 550       Uninterpreted_Data : System.Address;
 551       Mode               : Call_Modes)
 552    is
 553       Self_Id    : constant Task_Id := STPO.Self;
 554       Entry_Call : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 555    begin
 556       --  If pragma Detect_Blocking is active then Program_Error must be
 557       --  raised if this potentially blocking operation is called from a
 558       --  protected action.
 559
 560       if Detect_Blocking
 561         and then Self_Id.Common.Protected_Action_Nesting > 0
 562       then
 563          Ada.Exceptions.Raise_Exception
 564            (Program_Error'Identity, "potentially blocking operation");
 565       end if;
 566
 567       Lock_Entry (Object);
 568
 569       Entry_Call.Mode := Mode;
 570       Entry_Call.State := Now_Abortable;
 571       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 572       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 573
 574       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 575       Unlock_Entry (Object);
 576
 577       --  The call is either `Done' or not. It cannot be cancelled since there
 578       --  is no ATC construct.
 579
 580       pragma Assert (Entry_Call.State /= Cancelled);
 581
 582       if Entry_Call.State /= Done then
 583          if Single_Lock then
 584             STPO.Lock_RTS;
 585          end if;
 586
 587          STPO.Write_Lock (Self_Id);
 588          Wait_For_Completion (Entry_Call'Access);
 589          STPO.Unlock (Self_Id);
 590
 591          if Single_Lock then
 592             STPO.Unlock_RTS;
 593          end if;
 594       end if;
 595
 596       Check_Exception (Self_Id, Entry_Call'Access);
 597    end Protected_Single_Entry_Call;
 598
 599    -----------------------------------
 600    -- Protected_Single_Entry_Caller --
 601    -----------------------------------
 602
 603    function Protected_Single_Entry_Caller
 604      (Object : Protection_Entry) return Task_Id is
 605    begin
 606       return Object.Call_In_Progress.Self;
 607    end Protected_Single_Entry_Caller;
 608
 609    -------------------
 610    -- Service_Entry --
 611    -------------------
 612
 613    procedure Service_Entry (Object : Protection_Entry_Access) is
 614       Self_Id    : constant Task_Id := STPO.Self;
 615       Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;
 616       Caller     : Task_Id;
 617
 618    begin
 619       if Entry_Call /= null
 620         and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)
 621       then
 622          Object.Entry_Queue := null;
 623
 624          if Object.Call_In_Progress /= null then
 625
 626             --  Violation of No_Entry_Queue restriction, raise exception
 627
 628             Send_Program_Error (Self_Id, Entry_Call);
 629             Unlock_Entry (Object);
 630             return;
 631          end if;
 632
 633          Object.Call_In_Progress := Entry_Call;
 634          Object.Entry_Body.Action
 635            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 636          Object.Call_In_Progress := null;
 637          Caller := Entry_Call.Self;
 638          Unlock_Entry (Object);
 639
 640          if Single_Lock then
 641             STPO.Lock_RTS;
 642          end if;
 643
 644          STPO.Write_Lock (Caller);
 645          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 646          STPO.Unlock (Caller);
 647
 648          if Single_Lock then
 649             STPO.Unlock_RTS;
 650          end if;
 651
 652       else
 653          --  Just unlock the entry
 654
 655          Unlock_Entry (Object);
 656       end if;
 657
 658    exception
 659       when others =>
 660          Send_Program_Error (Self_Id, Entry_Call);
 661          Unlock_Entry (Object);
 662    end Service_Entry;
 663
 664    ---------------------------------------
 665    -- Timed_Protected_Single_Entry_Call --
 666    ---------------------------------------
 667
 668    --  Compiler interface only (do not call from within the RTS)
 669
 670    procedure Timed_Protected_Single_Entry_Call
 671      (Object                : Protection_Entry_Access;
 672       Uninterpreted_Data    : System.Address;
 673       Timeout               : Duration;
 674       Mode                  : Delay_Modes;
 675       Entry_Call_Successful : out Boolean)
 676    is
 677       Self_Id           : constant Task_Id  := STPO.Self;
 678       Entry_Call        : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 679       Ceiling_Violation : Boolean;
 680
 681    begin
 682       --  If pragma Detect_Blocking is active then Program_Error must be
 683       --  raised if this potentially blocking operation is called from a
 684       --  protected action.
 685
 686       if Detect_Blocking
 687         and then Self_Id.Common.Protected_Action_Nesting > 0
 688       then
 689          Ada.Exceptions.Raise_Exception
 690            (Program_Error'Identity, "potentially blocking operation");
 691       end if;
 692
 693       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 694
 695       if Ceiling_Violation then
 696          raise Program_Error;
 697       end if;
 698
 699       Entry_Call.Mode := Timed_Call;
 700       Entry_Call.State := Now_Abortable;
 701       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 702       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 703
 704       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 705       Unlock_Entry (Object);
 706
 707       --  Try to avoid waiting for completed calls.
 708       --  The call is either `Done' or not. It cannot be cancelled since there
 709       --  is no ATC construct and the timed wait has not started yet.
 710
 711       pragma Assert (Entry_Call.State /= Cancelled);
 712
 713       if Entry_Call.State = Done then
 714          Check_Exception (Self_Id, Entry_Call'Access);
 715          Entry_Call_Successful := True;
 716          return;
 717       end if;
 718
 719       if Single_Lock then
 720          STPO.Lock_RTS;
 721       else
 722          STPO.Write_Lock (Self_Id);
 723       end if;
 724
 725       Wait_For_Completion_With_Timeout (Entry_Call'Access, Timeout, Mode);
 726
 727       if Single_Lock then
 728          STPO.Unlock_RTS;
 729       else
 730          STPO.Unlock (Self_Id);
 731       end if;
 732
 733       pragma Assert (Entry_Call.State >= Done);
 734
 735       Check_Exception (Self_Id, Entry_Call'Access);
 736       Entry_Call_Successful := Entry_Call.State = Done;
 737    end Timed_Protected_Single_Entry_Call;
 738
 739    ------------------
 740    -- Unlock_Entry --
 741    ------------------
 742
 743    procedure Unlock_Entry (Object : Protection_Entry_Access) is
 744    begin
 745       --  We are exiting from a protected action, so that we decrease the
 746       --  protected object nesting level (if pragma Detect_Blocking is
 747       --  active), and remove ownership of the protected object.
 748
 749       if Detect_Blocking then
 750          declare
 751             Self_Id : constant Task_Id := Self;
 752
 753          begin
 754             --  Calls to this procedure can only take place when being within
 755             --  a protected action and when the caller is the protected
 756             --  object's owner.
 757
 758             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 759                              and then Object.Owner = Self_Id);
 760
 761             --  Remove ownership of the protected object
 762
 763             Object.Owner := Null_Task;
 764
 765             Self_Id.Common.Protected_Action_Nesting :=
 766               Self_Id.Common.Protected_Action_Nesting - 1;
 767          end;
 768       end if;
 769
 770       STPO.Unlock (Object.L'Access);
 771    end Unlock_Entry;
 772
 773 end System.Tasking.Protected_Objects.Single_Entry;