gcc/ada/s-tposen.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                  --
   4 --                                                                          --
   5 --             SYSTEM.TASKING.PROTECTED_OBJECTS.SINGLE_ENTRY                --
   6 --                                                                          --
   7 --                                B o d y                                   --
   8 --                                                                          --
   9 --         Copyright (C) 1998-2008, 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,  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 -- 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 Style_Checks (All_Checks);
  35 --  Turn off subprogram ordering check, since restricted GNARLI subprograms are
  36 --  gathered together at end.
  37
  38 --  This package provides an optimized version of Protected_Objects.Operations
  39 --  and Protected_Objects.Entries making the following assumptions:
  40
  41 --    PO has only one entry
  42 --    There is only one caller at a time (No_Entry_Queue)
  43 --    There is no dynamic priority support (No_Dynamic_Priorities)
  44 --    No Abort Statements
  45 --     (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)
  46 --    PO are at library level
  47 --    No Requeue
  48 --    None of the tasks will terminate (no need for finalization)
  49
  50 --  This interface is intended to be used in the ravenscar and restricted
  51 --  profiles, the compiler is responsible for ensuring that the conditions
  52 --  mentioned above are respected, except for the No_Entry_Queue restriction
  53 --  that is checked dynamically in this package, since the check cannot be
  54 --  performed at compile time, and is relatively cheap (see PO_Do_Or_Queue,
  55 --  Service_Entry).
  56
  57 pragma Polling (Off);
  58 --  Turn off polling, we do not want polling to take place during tasking
  59 --  operations. It can cause  infinite loops and other problems.
  60
  61 pragma Suppress (All_Checks);
  62 --  Why is this required ???
  63
  64 with Ada.Exceptions;
  65
  66 with System.Task_Primitives.Operations;
  67 with System.Parameters;
  68
  69 package body System.Tasking.Protected_Objects.Single_Entry is
  70
  71    package STPO renames System.Task_Primitives.Operations;
  72
  73    use Parameters;
  74
  75    -----------------------
  76    -- Local Subprograms --
  77    -----------------------
  78
  79    procedure Send_Program_Error
  80      (Self_Id    : Task_Id;
  81       Entry_Call : Entry_Call_Link);
  82    pragma Inline (Send_Program_Error);
  83    --  Raise Program_Error in the caller of the specified entry call
  84
  85    --------------------------
  86    -- Entry Calls Handling --
  87    --------------------------
  88
  89    procedure Wakeup_Entry_Caller
  90      (Self_ID    : Task_Id;
  91       Entry_Call : Entry_Call_Link;
  92       New_State  : Entry_Call_State);
  93    pragma Inline (Wakeup_Entry_Caller);
  94    --  This is called at the end of service of an entry call,
  95    --  to abort the caller if he is in an abortable part, and
  96    --  to wake up the caller if he is on Entry_Caller_Sleep.
  97    --  Call it holding the lock of Entry_Call.Self.
  98    --
  99    --  Timed_Call or Simple_Call:
 100    --    The caller is waiting on Entry_Caller_Sleep, in
 101    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 102
 103    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link);
 104    pragma Inline (Wait_For_Completion);
 105    --  This procedure suspends the calling task until the specified entry call
 106    --  has either been completed or cancelled. On exit, the call will not be
 107    --  queued. This waits for calls on protected entries.
 108    --  Call this only when holding Self_ID locked.
 109
 110    procedure Wait_For_Completion_With_Timeout
 111      (Entry_Call  : Entry_Call_Link;
 112       Wakeup_Time : Duration;
 113       Mode        : Delay_Modes);
 114    --  Same as Wait_For_Completion but it waits for a timeout with the value
 115    --  specified in Wakeup_Time as well.
 116
 117    procedure Check_Exception
 118      (Self_ID : Task_Id;
 119       Entry_Call : Entry_Call_Link);
 120    pragma Inline (Check_Exception);
 121    --  Raise any pending exception from the Entry_Call.
 122    --  This should be called at the end of every compiler interface procedure
 123    --  that implements an entry call.
 124    --  The caller should not be holding any locks, or there will be deadlock.
 125
 126    procedure PO_Do_Or_Queue
 127      (Self_Id    : Task_Id;
 128       Object     : Protection_Entry_Access;
 129       Entry_Call : Entry_Call_Link);
 130    --  This procedure executes or queues an entry call, depending
 131    --  on the status of the corresponding barrier. It assumes that the
 132    --  specified object is locked.
 133
 134    ---------------------
 135    -- Check_Exception --
 136    ---------------------
 137
 138    procedure Check_Exception
 139      (Self_ID    : Task_Id;
 140       Entry_Call : Entry_Call_Link)
 141    is
 142       pragma Warnings (Off, Self_ID);
 143
 144       procedure Internal_Raise (X : Ada.Exceptions.Exception_Id);
 145       pragma Import (C, Internal_Raise, "__gnat_raise_with_msg");
 146
 147       use type Ada.Exceptions.Exception_Id;
 148
 149       E : constant Ada.Exceptions.Exception_Id :=
 150             Entry_Call.Exception_To_Raise;
 151
 152    begin
 153       if E /= Ada.Exceptions.Null_Id then
 154          Internal_Raise (E);
 155       end if;
 156    end Check_Exception;
 157
 158    ------------------------
 159    -- Send_Program_Error --
 160    ------------------------
 161
 162    procedure Send_Program_Error
 163      (Self_Id    : Task_Id;
 164       Entry_Call : Entry_Call_Link)
 165    is
 166       Caller : constant Task_Id := Entry_Call.Self;
 167    begin
 168       Entry_Call.Exception_To_Raise := Program_Error'Identity;
 169
 170       if Single_Lock then
 171          STPO.Lock_RTS;
 172       end if;
 173
 174       STPO.Write_Lock (Caller);
 175       Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 176       STPO.Unlock (Caller);
 177
 178       if Single_Lock then
 179          STPO.Unlock_RTS;
 180       end if;
 181    end Send_Program_Error;
 182
 183    -------------------------
 184    -- Wait_For_Completion --
 185    -------------------------
 186
 187    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is
 188       Self_Id : constant Task_Id := Entry_Call.Self;
 189    begin
 190       Self_Id.Common.State := Entry_Caller_Sleep;
 191       STPO.Sleep (Self_Id, Entry_Caller_Sleep);
 192       Self_Id.Common.State := Runnable;
 193    end Wait_For_Completion;
 194
 195    --------------------------------------
 196    -- Wait_For_Completion_With_Timeout --
 197    --------------------------------------
 198
 199    procedure Wait_For_Completion_With_Timeout
 200      (Entry_Call  : Entry_Call_Link;
 201       Wakeup_Time : Duration;
 202       Mode        : Delay_Modes)
 203    is
 204       Self_Id  : constant Task_Id := Entry_Call.Self;
 205       Timedout : Boolean;
 206
 207       Yielded  : Boolean;
 208       pragma Unreferenced (Yielded);
 209
 210       use type Ada.Exceptions.Exception_Id;
 211
 212    begin
 213       --  This procedure waits for the entry call to be served, with a timeout.
 214       --  It tries to cancel the call if the timeout expires before the call is
 215       --  served.
 216
 217       --  If we wake up from the timed sleep operation here, it may be for the
 218       --  following possible reasons:
 219
 220       --  1) The entry call is done being served.
 221       --  2) The timeout has expired (Timedout = True)
 222
 223       --  Once the timeout has expired we may need to continue to wait if the
 224       --  call is already being serviced. In that case, we want to go back to
 225       --  sleep, but without any timeout. The variable Timedout is used to
 226       --  control this. If the Timedout flag is set, we do not need to Sleep
 227       --  with a timeout. We just sleep until we get a wakeup for some status
 228       --  change.
 229
 230       pragma Assert (Entry_Call.Mode = Timed_Call);
 231       Self_Id.Common.State := Entry_Caller_Sleep;
 232
 233       STPO.Timed_Sleep
 234         (Self_Id, Wakeup_Time, Mode, Entry_Caller_Sleep, Timedout, Yielded);
 235
 236       if Timedout then
 237          Entry_Call.State := Cancelled;
 238       else
 239          Entry_Call.State := Done;
 240       end if;
 241
 242       Self_Id.Common.State := Runnable;
 243    end Wait_For_Completion_With_Timeout;
 244
 245    -------------------------
 246    -- Wakeup_Entry_Caller --
 247    -------------------------
 248
 249    --  This is called at the end of service of an entry call, to abort the
 250    --  caller if he is in an abortable part, and to wake up the caller if it
 251    --  is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
 252
 253    --  (This enforces the rule that a task must be off-queue if its state is
 254    --  Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
 255
 256    --  Timed_Call or Simple_Call:
 257    --    The caller is waiting on Entry_Caller_Sleep, in
 258    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 259
 260    --  Conditional_Call:
 261    --    The caller might be in Wait_For_Completion,
 262    --    waiting for a rendezvous (possibly requeued without abort)
 263    --    to complete.
 264
 265    procedure Wakeup_Entry_Caller
 266      (Self_ID    : Task_Id;
 267       Entry_Call : Entry_Call_Link;
 268       New_State  : Entry_Call_State)
 269    is
 270       pragma Warnings (Off, Self_ID);
 271
 272       Caller : constant Task_Id := Entry_Call.Self;
 273
 274    begin
 275       pragma Assert (New_State = Done or else New_State = Cancelled);
 276       pragma Assert
 277         (Caller.Common.State /= Terminated and then
 278          Caller.Common.State /= Unactivated);
 279
 280       Entry_Call.State := New_State;
 281       STPO.Wakeup (Caller, Entry_Caller_Sleep);
 282    end Wakeup_Entry_Caller;
 283
 284    -----------------------
 285    -- Restricted GNARLI --
 286    -----------------------
 287
 288    --------------------------------
 289    -- Complete_Single_Entry_Body --
 290    --------------------------------
 291
 292    procedure Complete_Single_Entry_Body (Object : Protection_Entry_Access) is
 293       pragma Warnings (Off, Object);
 294
 295    begin
 296       --  Nothing needs to do (Object.Call_In_Progress.Exception_To_Raise
 297       --  has already been set to Null_Id).
 298
 299       null;
 300    end Complete_Single_Entry_Body;
 301
 302    --------------------------------------------
 303    -- Exceptional_Complete_Single_Entry_Body --
 304    --------------------------------------------
 305
 306    procedure Exceptional_Complete_Single_Entry_Body
 307      (Object : Protection_Entry_Access;
 308       Ex     : Ada.Exceptions.Exception_Id) is
 309    begin
 310       Object.Call_In_Progress.Exception_To_Raise := Ex;
 311    end Exceptional_Complete_Single_Entry_Body;
 312
 313    ---------------------------------
 314    -- Initialize_Protection_Entry --
 315    ---------------------------------
 316
 317    procedure Initialize_Protection_Entry
 318      (Object            : Protection_Entry_Access;
 319       Ceiling_Priority  : Integer;
 320       Compiler_Info     : System.Address;
 321       Entry_Body        : Entry_Body_Access)
 322    is
 323       Init_Priority : Integer := Ceiling_Priority;
 324    begin
 325       if Init_Priority = Unspecified_Priority then
 326          Init_Priority := System.Priority'Last;
 327       end if;
 328
 329       STPO.Initialize_Lock (Init_Priority, Object.L'Access);
 330       Object.Ceiling := System.Any_Priority (Init_Priority);
 331       Object.Owner := Null_Task;
 332       Object.Compiler_Info := Compiler_Info;
 333       Object.Call_In_Progress := null;
 334       Object.Entry_Body := Entry_Body;
 335       Object.Entry_Queue := null;
 336    end Initialize_Protection_Entry;
 337
 338    ----------------
 339    -- Lock_Entry --
 340    ----------------
 341
 342    --  Compiler interface only.
 343    --  Do not call this procedure from within the run-time system.
 344
 345    procedure Lock_Entry (Object : Protection_Entry_Access) is
 346       Ceiling_Violation : Boolean;
 347
 348    begin
 349       --  If pragma Detect_Blocking is active then, as described in the ARM
 350       --  9.5.1, par. 15, we must check whether this is an external call on a
 351       --  protected subprogram with the same target object as that of the
 352       --  protected action that is currently in progress (i.e., if the caller
 353       --  is already the protected object's owner). If this is the case hence
 354       --  Program_Error must be raised.
 355
 356       if Detect_Blocking and then Object.Owner = Self then
 357          raise Program_Error;
 358       end if;
 359
 360       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 361
 362       if Ceiling_Violation then
 363          raise Program_Error;
 364       end if;
 365
 366       --  We are entering in a protected action, so that we increase the
 367       --  protected object nesting level (if pragma Detect_Blocking is
 368       --  active), and update the protected object's owner.
 369
 370       if Detect_Blocking then
 371          declare
 372             Self_Id : constant Task_Id := Self;
 373
 374          begin
 375             --  Update the protected object's owner
 376
 377             Object.Owner := Self_Id;
 378
 379             --  Increase protected object nesting level
 380
 381             Self_Id.Common.Protected_Action_Nesting :=
 382               Self_Id.Common.Protected_Action_Nesting + 1;
 383          end;
 384       end if;
 385    end Lock_Entry;
 386
 387    --------------------------
 388    -- Lock_Read_Only_Entry --
 389    --------------------------
 390
 391    --  Compiler interface only
 392
 393    --  Do not call this procedure from within the runtime system
 394
 395    procedure Lock_Read_Only_Entry (Object : Protection_Entry_Access) is
 396       Ceiling_Violation : Boolean;
 397
 398    begin
 399       --  If pragma Detect_Blocking is active then, as described in the ARM
 400       --  9.5.1, par. 15, we must check whether this is an external call on a
 401       --  protected subprogram with the same target object as that of the
 402       --  protected action that is currently in progress (i.e., if the caller
 403       --  is already the protected object's owner). If this is the case hence
 404       --  Program_Error must be raised.
 405
 406       --  Note that in this case (getting read access), several tasks may
 407       --  have read ownership of the protected object, so that this method of
 408       --  storing the (single) protected object's owner does not work
 409       --  reliably for read locks. However, this is the approach taken for two
 410       --  major reasons: first, this function is not currently being used (it
 411       --  is provided for possible future use), and second, it largely
 412       --  simplifies the implementation.
 413
 414       if Detect_Blocking and then Object.Owner = Self then
 415          raise Program_Error;
 416       end if;
 417
 418       STPO.Read_Lock (Object.L'Access, Ceiling_Violation);
 419
 420       if Ceiling_Violation then
 421          raise Program_Error;
 422       end if;
 423
 424       --  We are entering in a protected action, so that we increase the
 425       --  protected object nesting level (if pragma Detect_Blocking is
 426       --  active), and update the protected object's owner.
 427
 428       if Detect_Blocking then
 429          declare
 430             Self_Id : constant Task_Id := Self;
 431
 432          begin
 433             --  Update the protected object's owner
 434
 435             Object.Owner := Self_Id;
 436
 437             --  Increase protected object nesting level
 438
 439             Self_Id.Common.Protected_Action_Nesting :=
 440               Self_Id.Common.Protected_Action_Nesting + 1;
 441          end;
 442       end if;
 443    end Lock_Read_Only_Entry;
 444
 445    --------------------
 446    -- PO_Do_Or_Queue --
 447    --------------------
 448
 449    procedure PO_Do_Or_Queue
 450      (Self_Id    : Task_Id;
 451       Object     : Protection_Entry_Access;
 452       Entry_Call : Entry_Call_Link)
 453    is
 454       Barrier_Value : Boolean;
 455
 456    begin
 457       --  When the Action procedure for an entry body returns, it must be
 458       --  completed (having called [Exceptional_]Complete_Entry_Body).
 459
 460       Barrier_Value := Object.Entry_Body.Barrier (Object.Compiler_Info, 1);
 461
 462       if Barrier_Value then
 463          if Object.Call_In_Progress /= null then
 464
 465             --  This violates the No_Entry_Queue restriction, send
 466             --  Program_Error to the caller.
 467
 468             Send_Program_Error (Self_Id, Entry_Call);
 469             return;
 470          end if;
 471
 472          Object.Call_In_Progress := Entry_Call;
 473          Object.Entry_Body.Action
 474            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 475          Object.Call_In_Progress := null;
 476
 477          if Single_Lock then
 478             STPO.Lock_RTS;
 479          end if;
 480
 481          STPO.Write_Lock (Entry_Call.Self);
 482          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 483          STPO.Unlock (Entry_Call.Self);
 484
 485          if Single_Lock then
 486             STPO.Unlock_RTS;
 487          end if;
 488
 489       elsif Entry_Call.Mode /= Conditional_Call then
 490          if Object.Entry_Queue /= null then
 491
 492             --  This violates the No_Entry_Queue restriction, send
 493             --  Program_Error to the caller.
 494
 495             Send_Program_Error (Self_Id, Entry_Call);
 496             return;
 497          else
 498             Object.Entry_Queue := Entry_Call;
 499          end if;
 500
 501       else
 502          --  Conditional_Call
 503
 504          if Single_Lock then
 505             STPO.Lock_RTS;
 506          end if;
 507
 508          STPO.Write_Lock (Entry_Call.Self);
 509          Wakeup_Entry_Caller (Self_Id, Entry_Call, Cancelled);
 510          STPO.Unlock (Entry_Call.Self);
 511
 512          if Single_Lock then
 513             STPO.Unlock_RTS;
 514          end if;
 515       end if;
 516
 517    exception
 518       when others =>
 519          Send_Program_Error
 520            (Self_Id, Entry_Call);
 521    end PO_Do_Or_Queue;
 522
 523    ----------------------------
 524    -- Protected_Single_Count --
 525    ----------------------------
 526
 527    function Protected_Count_Entry (Object : Protection_Entry) return Natural is
 528    begin
 529       if Object.Entry_Queue /= null then
 530          return 1;
 531       else
 532          return 0;
 533       end if;
 534    end Protected_Count_Entry;
 535
 536    ---------------------------------
 537    -- Protected_Single_Entry_Call --
 538    ---------------------------------
 539
 540    procedure Protected_Single_Entry_Call
 541      (Object             : Protection_Entry_Access;
 542       Uninterpreted_Data : System.Address;
 543       Mode               : Call_Modes)
 544    is
 545       Self_Id    : constant Task_Id := STPO.Self;
 546       Entry_Call : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 547    begin
 548       --  If pragma Detect_Blocking is active then Program_Error must be
 549       --  raised if this potentially blocking operation is called from a
 550       --  protected action.
 551
 552       if Detect_Blocking
 553         and then Self_Id.Common.Protected_Action_Nesting > 0
 554       then
 555          raise Program_Error with "potentially blocking operation";
 556       end if;
 557
 558       Lock_Entry (Object);
 559
 560       Entry_Call.Mode := Mode;
 561       Entry_Call.State := Now_Abortable;
 562       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 563       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 564
 565       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 566       Unlock_Entry (Object);
 567
 568       --  The call is either `Done' or not. It cannot be cancelled since there
 569       --  is no ATC construct.
 570
 571       pragma Assert (Entry_Call.State /= Cancelled);
 572
 573       if Entry_Call.State /= Done then
 574          if Single_Lock then
 575             STPO.Lock_RTS;
 576          end if;
 577
 578          STPO.Write_Lock (Self_Id);
 579          Wait_For_Completion (Entry_Call'Access);
 580          STPO.Unlock (Self_Id);
 581
 582          if Single_Lock then
 583             STPO.Unlock_RTS;
 584          end if;
 585       end if;
 586
 587       Check_Exception (Self_Id, Entry_Call'Access);
 588    end Protected_Single_Entry_Call;
 589
 590    -----------------------------------
 591    -- Protected_Single_Entry_Caller --
 592    -----------------------------------
 593
 594    function Protected_Single_Entry_Caller
 595      (Object : Protection_Entry) return Task_Id is
 596    begin
 597       return Object.Call_In_Progress.Self;
 598    end Protected_Single_Entry_Caller;
 599
 600    -------------------
 601    -- Service_Entry --
 602    -------------------
 603
 604    procedure Service_Entry (Object : Protection_Entry_Access) is
 605       Self_Id    : constant Task_Id := STPO.Self;
 606       Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;
 607       Caller     : Task_Id;
 608
 609    begin
 610       if Entry_Call /= null
 611         and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)
 612       then
 613          Object.Entry_Queue := null;
 614
 615          if Object.Call_In_Progress /= null then
 616
 617             --  Violation of No_Entry_Queue restriction, raise exception
 618
 619             Send_Program_Error (Self_Id, Entry_Call);
 620             Unlock_Entry (Object);
 621             return;
 622          end if;
 623
 624          Object.Call_In_Progress := Entry_Call;
 625          Object.Entry_Body.Action
 626            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 627          Object.Call_In_Progress := null;
 628          Caller := Entry_Call.Self;
 629          Unlock_Entry (Object);
 630
 631          if Single_Lock then
 632             STPO.Lock_RTS;
 633          end if;
 634
 635          STPO.Write_Lock (Caller);
 636          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 637          STPO.Unlock (Caller);
 638
 639          if Single_Lock then
 640             STPO.Unlock_RTS;
 641          end if;
 642
 643       else
 644          --  Just unlock the entry
 645
 646          Unlock_Entry (Object);
 647       end if;
 648
 649    exception
 650       when others =>
 651          Send_Program_Error (Self_Id, Entry_Call);
 652          Unlock_Entry (Object);
 653    end Service_Entry;
 654
 655    ---------------------------------------
 656    -- Timed_Protected_Single_Entry_Call --
 657    ---------------------------------------
 658
 659    --  Compiler interface only (do not call from within the RTS)
 660
 661    procedure Timed_Protected_Single_Entry_Call
 662      (Object                : Protection_Entry_Access;
 663       Uninterpreted_Data    : System.Address;
 664       Timeout               : Duration;
 665       Mode                  : Delay_Modes;
 666       Entry_Call_Successful : out Boolean)
 667    is
 668       Self_Id           : constant Task_Id  := STPO.Self;
 669       Entry_Call        : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 670       Ceiling_Violation : Boolean;
 671
 672    begin
 673       --  If pragma Detect_Blocking is active then Program_Error must be
 674       --  raised if this potentially blocking operation is called from a
 675       --  protected action.
 676
 677       if Detect_Blocking
 678         and then Self_Id.Common.Protected_Action_Nesting > 0
 679       then
 680          raise Program_Error with "potentially blocking operation";
 681       end if;
 682
 683       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 684
 685       if Ceiling_Violation then
 686          raise Program_Error;
 687       end if;
 688
 689       Entry_Call.Mode := Timed_Call;
 690       Entry_Call.State := Now_Abortable;
 691       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 692       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 693
 694       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 695       Unlock_Entry (Object);
 696
 697       --  Try to avoid waiting for completed calls.
 698       --  The call is either `Done' or not. It cannot be cancelled since there
 699       --  is no ATC construct and the timed wait has not started yet.
 700
 701       pragma Assert (Entry_Call.State /= Cancelled);
 702
 703       if Entry_Call.State = Done then
 704          Check_Exception (Self_Id, Entry_Call'Access);
 705          Entry_Call_Successful := True;
 706          return;
 707       end if;
 708
 709       if Single_Lock then
 710          STPO.Lock_RTS;
 711       else
 712          STPO.Write_Lock (Self_Id);
 713       end if;
 714
 715       Wait_For_Completion_With_Timeout (Entry_Call'Access, Timeout, Mode);
 716
 717       if Single_Lock then
 718          STPO.Unlock_RTS;
 719       else
 720          STPO.Unlock (Self_Id);
 721       end if;
 722
 723       pragma Assert (Entry_Call.State >= Done);
 724
 725       Check_Exception (Self_Id, Entry_Call'Access);
 726       Entry_Call_Successful := Entry_Call.State = Done;
 727    end Timed_Protected_Single_Entry_Call;
 728
 729    ------------------
 730    -- Unlock_Entry --
 731    ------------------
 732
 733    procedure Unlock_Entry (Object : Protection_Entry_Access) is
 734    begin
 735       --  We are exiting from a protected action, so that we decrease the
 736       --  protected object nesting level (if pragma Detect_Blocking is
 737       --  active), and remove ownership of the protected object.
 738
 739       if Detect_Blocking then
 740          declare
 741             Self_Id : constant Task_Id := Self;
 742
 743          begin
 744             --  Calls to this procedure can only take place when being within
 745             --  a protected action and when the caller is the protected
 746             --  object's owner.
 747
 748             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 749                              and then Object.Owner = Self_Id);
 750
 751             --  Remove ownership of the protected object
 752
 753             Object.Owner := Null_Task;
 754
 755             Self_Id.Common.Protected_Action_Nesting :=
 756               Self_Id.Common.Protected_Action_Nesting - 1;
 757          end;
 758       end if;
 759
 760       STPO.Unlock (Object.L'Access);
 761    end Unlock_Entry;
 762
 763 end System.Tasking.Protected_Objects.Single_Entry;