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) 1998-2005, 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       Yielded  : Boolean;
 215
 216       use type Ada.Exceptions.Exception_Id;
 217
 218    begin
 219       --  This procedure waits for the entry call to be served, with a timeout.
 220       --  It tries to cancel the call if the timeout expires before the call is
 221       --  served.
 222
 223       --  If we wake up from the timed sleep operation here, it may be for the
 224       --  following possible reasons:
 225
 226       --  1) The entry call is done being served.
 227       --  2) The timeout has expired (Timedout = True)
 228
 229       --  Once the timeout has expired we may need to continue to wait if the
 230       --  call is already being serviced. In that case, we want to go back to
 231       --  sleep, but without any timeout. The variable Timedout is used to
 232       --  control this. If the Timedout flag is set, we do not need to Sleep
 233       --  with a timeout. We just sleep until we get a wakeup for some status
 234       --  change.
 235
 236       pragma Assert (Entry_Call.Mode = Timed_Call);
 237       Self_Id.Common.State := Entry_Caller_Sleep;
 238
 239       STPO.Timed_Sleep
 240         (Self_Id, Wakeup_Time, Mode, Entry_Caller_Sleep, Timedout, Yielded);
 241
 242       if Timedout then
 243          Entry_Call.State := Cancelled;
 244       else
 245          Entry_Call.State := Done;
 246       end if;
 247
 248       Self_Id.Common.State := Runnable;
 249    end Wait_For_Completion_With_Timeout;
 250
 251    -------------------------
 252    -- Wakeup_Entry_Caller --
 253    -------------------------
 254
 255    --  This is called at the end of service of an entry call, to abort the
 256    --  caller if he is in an abortable part, and to wake up the caller if it
 257    --  is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
 258
 259    --  (This enforces the rule that a task must be off-queue if its state is
 260    --  Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
 261
 262    --  Timed_Call or Simple_Call:
 263    --    The caller is waiting on Entry_Caller_Sleep, in
 264    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 265
 266    --  Conditional_Call:
 267    --    The caller might be in Wait_For_Completion,
 268    --    waiting for a rendezvous (possibly requeued without abort)
 269    --    to complete.
 270
 271    procedure Wakeup_Entry_Caller
 272      (Self_ID    : Task_Id;
 273       Entry_Call : Entry_Call_Link;
 274       New_State  : Entry_Call_State)
 275    is
 276       pragma Warnings (Off, Self_ID);
 277
 278       Caller : constant Task_Id := Entry_Call.Self;
 279
 280    begin
 281       pragma Assert (New_State = Done or else New_State = Cancelled);
 282       pragma Assert
 283         (Caller.Common.State /= Terminated and then
 284          Caller.Common.State /= Unactivated);
 285
 286       Entry_Call.State := New_State;
 287       STPO.Wakeup (Caller, Entry_Caller_Sleep);
 288    end Wakeup_Entry_Caller;
 289
 290    -----------------------
 291    -- Restricted GNARLI --
 292    -----------------------
 293
 294    --------------------------------
 295    -- Complete_Single_Entry_Body --
 296    --------------------------------
 297
 298    procedure Complete_Single_Entry_Body (Object : Protection_Entry_Access) is
 299       pragma Warnings (Off, Object);
 300
 301    begin
 302       --  Nothing needs to do (Object.Call_In_Progress.Exception_To_Raise
 303       --  has already been set to Null_Id).
 304
 305       null;
 306    end Complete_Single_Entry_Body;
 307
 308    --------------------------------------------
 309    -- Exceptional_Complete_Single_Entry_Body --
 310    --------------------------------------------
 311
 312    procedure Exceptional_Complete_Single_Entry_Body
 313      (Object : Protection_Entry_Access;
 314       Ex     : Ada.Exceptions.Exception_Id) is
 315    begin
 316       Object.Call_In_Progress.Exception_To_Raise := Ex;
 317    end Exceptional_Complete_Single_Entry_Body;
 318
 319    ---------------------------------
 320    -- Initialize_Protection_Entry --
 321    ---------------------------------
 322
 323    procedure Initialize_Protection_Entry
 324      (Object            : Protection_Entry_Access;
 325       Ceiling_Priority  : Integer;
 326       Compiler_Info     : System.Address;
 327       Entry_Body        : Entry_Body_Access)
 328    is
 329       Init_Priority : Integer := Ceiling_Priority;
 330    begin
 331       if Init_Priority = Unspecified_Priority then
 332          Init_Priority := System.Priority'Last;
 333       end if;
 334
 335       STPO.Initialize_Lock (Init_Priority, Object.L'Access);
 336       Object.Ceiling := System.Any_Priority (Init_Priority);
 337       Object.Owner := Null_Task;
 338       Object.Compiler_Info := Compiler_Info;
 339       Object.Call_In_Progress := null;
 340       Object.Entry_Body := Entry_Body;
 341       Object.Entry_Queue := null;
 342    end Initialize_Protection_Entry;
 343
 344    ----------------
 345    -- Lock_Entry --
 346    ----------------
 347
 348    --  Compiler interface only.
 349    --  Do not call this procedure from within the run-time system.
 350
 351    procedure Lock_Entry (Object : Protection_Entry_Access) is
 352       Ceiling_Violation : Boolean;
 353
 354    begin
 355       --  If pragma Detect_Blocking is active then, as described in the ARM
 356       --  9.5.1, par. 15, we must check whether this is an external call on a
 357       --  protected subprogram with the same target object as that of the
 358       --  protected action that is currently in progress (i.e., if the caller
 359       --  is already the protected object's owner). If this is the case hence
 360       --  Program_Error must be raised.
 361
 362       if Detect_Blocking and then Object.Owner = Self then
 363          raise Program_Error;
 364       end if;
 365
 366       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 367
 368       if Ceiling_Violation then
 369          raise Program_Error;
 370       end if;
 371
 372       --  We are entering in a protected action, so that we increase the
 373       --  protected object nesting level (if pragma Detect_Blocking is
 374       --  active), and update the protected object's owner.
 375
 376       if Detect_Blocking then
 377          declare
 378             Self_Id : constant Task_Id := Self;
 379
 380          begin
 381             --  Update the protected object's owner
 382
 383             Object.Owner := Self_Id;
 384
 385             --  Increase protected object nesting level
 386
 387             Self_Id.Common.Protected_Action_Nesting :=
 388               Self_Id.Common.Protected_Action_Nesting + 1;
 389          end;
 390       end if;
 391    end Lock_Entry;
 392
 393    --------------------------
 394    -- Lock_Read_Only_Entry --
 395    --------------------------
 396
 397    --  Compiler interface only
 398
 399    --  Do not call this procedure from within the runtime system
 400
 401    procedure Lock_Read_Only_Entry (Object : Protection_Entry_Access) is
 402       Ceiling_Violation : Boolean;
 403
 404    begin
 405       --  If pragma Detect_Blocking is active then, as described in the ARM
 406       --  9.5.1, par. 15, we must check whether this is an external call on a
 407       --  protected subprogram with the same target object as that of the
 408       --  protected action that is currently in progress (i.e., if the caller
 409       --  is already the protected object's owner). If this is the case hence
 410       --  Program_Error must be raised.
 411
 412       --  Note that in this case (getting read access), several tasks may
 413       --  have read ownership of the protected object, so that this method of
 414       --  storing the (single) protected object's owner does not work
 415       --  reliably for read locks. However, this is the approach taken for two
 416       --  major reasosn: first, this function is not currently being used (it
 417       --  is provided for possible future use), and second, it largely
 418       --  simplifies the implementation.
 419
 420       if Detect_Blocking and then Object.Owner = Self then
 421          raise Program_Error;
 422       end if;
 423
 424       STPO.Read_Lock (Object.L'Access, Ceiling_Violation);
 425
 426       if Ceiling_Violation then
 427          raise Program_Error;
 428       end if;
 429
 430       --  We are entering in a protected action, so that we increase the
 431       --  protected object nesting level (if pragma Detect_Blocking is
 432       --  active), and update the protected object's owner.
 433
 434       if Detect_Blocking then
 435          declare
 436             Self_Id : constant Task_Id := Self;
 437
 438          begin
 439             --  Update the protected object's owner
 440
 441             Object.Owner := Self_Id;
 442
 443             --  Increase protected object nesting level
 444
 445             Self_Id.Common.Protected_Action_Nesting :=
 446               Self_Id.Common.Protected_Action_Nesting + 1;
 447          end;
 448       end if;
 449    end Lock_Read_Only_Entry;
 450
 451    --------------------
 452    -- PO_Do_Or_Queue --
 453    --------------------
 454
 455    procedure PO_Do_Or_Queue
 456      (Self_Id    : Task_Id;
 457       Object     : Protection_Entry_Access;
 458       Entry_Call : Entry_Call_Link)
 459    is
 460       Barrier_Value : Boolean;
 461
 462    begin
 463       --  When the Action procedure for an entry body returns, it must be
 464       --  completed (having called [Exceptional_]Complete_Entry_Body).
 465
 466       Barrier_Value := Object.Entry_Body.Barrier (Object.Compiler_Info, 1);
 467
 468       if Barrier_Value then
 469          if Object.Call_In_Progress /= null then
 470
 471             --  This violates the No_Entry_Queue restriction, send
 472             --  Program_Error to the caller.
 473
 474             Send_Program_Error (Self_Id, Entry_Call);
 475             return;
 476          end if;
 477
 478          Object.Call_In_Progress := Entry_Call;
 479          Object.Entry_Body.Action
 480            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 481          Object.Call_In_Progress := null;
 482
 483          if Single_Lock then
 484             STPO.Lock_RTS;
 485          end if;
 486
 487          STPO.Write_Lock (Entry_Call.Self);
 488          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 489          STPO.Unlock (Entry_Call.Self);
 490
 491          if Single_Lock then
 492             STPO.Unlock_RTS;
 493          end if;
 494
 495       elsif Entry_Call.Mode /= Conditional_Call then
 496          if Object.Entry_Queue /= null then
 497
 498             --  This violates the No_Entry_Queue restriction, send
 499             --  Program_Error to the caller.
 500
 501             Send_Program_Error (Self_Id, Entry_Call);
 502             return;
 503          else
 504             Object.Entry_Queue := Entry_Call;
 505          end if;
 506
 507       else
 508          --  Conditional_Call
 509
 510          if Single_Lock then
 511             STPO.Lock_RTS;
 512          end if;
 513
 514          STPO.Write_Lock (Entry_Call.Self);
 515          Wakeup_Entry_Caller (Self_Id, Entry_Call, Cancelled);
 516          STPO.Unlock (Entry_Call.Self);
 517
 518          if Single_Lock then
 519             STPO.Unlock_RTS;
 520          end if;
 521       end if;
 522
 523    exception
 524       when others =>
 525          Send_Program_Error
 526            (Self_Id, Entry_Call);
 527    end PO_Do_Or_Queue;
 528
 529    ----------------------------
 530    -- Protected_Single_Count --
 531    ----------------------------
 532
 533    function Protected_Count_Entry (Object : Protection_Entry) return Natural is
 534    begin
 535       if Object.Entry_Queue /= null then
 536          return 1;
 537       else
 538          return 0;
 539       end if;
 540    end Protected_Count_Entry;
 541
 542    ---------------------------------
 543    -- Protected_Single_Entry_Call --
 544    ---------------------------------
 545
 546    procedure Protected_Single_Entry_Call
 547      (Object             : Protection_Entry_Access;
 548       Uninterpreted_Data : System.Address;
 549       Mode               : Call_Modes)
 550    is
 551       Self_Id           : constant Task_Id := STPO.Self;
 552       Entry_Call        : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 553       Ceiling_Violation : Boolean;
 554
 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       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 568
 569       if Ceiling_Violation then
 570          raise Program_Error;
 571       end if;
 572
 573       Entry_Call.Mode := Mode;
 574       Entry_Call.State := Now_Abortable;
 575       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 576       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 577
 578       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 579       Unlock_Entry (Object);
 580
 581       --  The call is either `Done' or not. It cannot be cancelled since there
 582       --  is no ATC construct.
 583
 584       pragma Assert (Entry_Call.State /= Cancelled);
 585
 586       if Entry_Call.State /= Done then
 587          if Single_Lock then
 588             STPO.Lock_RTS;
 589          end if;
 590
 591          STPO.Write_Lock (Self_Id);
 592          Wait_For_Completion (Entry_Call'Access);
 593          STPO.Unlock (Self_Id);
 594
 595          if Single_Lock then
 596             STPO.Unlock_RTS;
 597          end if;
 598       end if;
 599
 600       Check_Exception (Self_Id, Entry_Call'Access);
 601    end Protected_Single_Entry_Call;
 602
 603    -----------------------------------
 604    -- Protected_Single_Entry_Caller --
 605    -----------------------------------
 606
 607    function Protected_Single_Entry_Caller
 608      (Object : Protection_Entry) return Task_Id is
 609    begin
 610       return Object.Call_In_Progress.Self;
 611    end Protected_Single_Entry_Caller;
 612
 613    -------------------
 614    -- Service_Entry --
 615    -------------------
 616
 617    procedure Service_Entry (Object : Protection_Entry_Access) is
 618       Self_Id    : constant Task_Id := STPO.Self;
 619       Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;
 620       Caller     : Task_Id;
 621
 622    begin
 623       if Entry_Call /= null
 624         and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)
 625       then
 626          Object.Entry_Queue := null;
 627
 628          if Object.Call_In_Progress /= null then
 629
 630             --  Violation of No_Entry_Queue restriction, raise exception
 631
 632             Send_Program_Error (Self_Id, Entry_Call);
 633             Unlock_Entry (Object);
 634             return;
 635          end if;
 636
 637          Object.Call_In_Progress := Entry_Call;
 638          Object.Entry_Body.Action
 639            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 640          Object.Call_In_Progress := null;
 641          Caller := Entry_Call.Self;
 642          Unlock_Entry (Object);
 643
 644          if Single_Lock then
 645             STPO.Lock_RTS;
 646          end if;
 647
 648          STPO.Write_Lock (Caller);
 649          Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);
 650          STPO.Unlock (Caller);
 651
 652          if Single_Lock then
 653             STPO.Unlock_RTS;
 654          end if;
 655
 656       else
 657          --  Just unlock the entry
 658
 659          Unlock_Entry (Object);
 660       end if;
 661
 662    exception
 663       when others =>
 664          Send_Program_Error (Self_Id, Entry_Call);
 665          Unlock_Entry (Object);
 666    end Service_Entry;
 667
 668    ---------------------------------------
 669    -- Timed_Protected_Single_Entry_Call --
 670    ---------------------------------------
 671
 672    --  Compiler interface only. Do not call from within the RTS.
 673
 674    procedure Timed_Protected_Single_Entry_Call
 675      (Object                : Protection_Entry_Access;
 676       Uninterpreted_Data    : System.Address;
 677       Timeout               : Duration;
 678       Mode                  : Delay_Modes;
 679       Entry_Call_Successful : out Boolean)
 680    is
 681       Self_Id           : constant Task_Id  := STPO.Self;
 682       Entry_Call        : Entry_Call_Record renames Self_Id.Entry_Calls (1);
 683       Ceiling_Violation : Boolean;
 684
 685    begin
 686       --  If pragma Detect_Blocking is active then Program_Error must be
 687       --  raised if this potentially blocking operation is called from a
 688       --  protected action.
 689
 690       if Detect_Blocking
 691         and then Self_Id.Common.Protected_Action_Nesting > 0
 692       then
 693          Ada.Exceptions.Raise_Exception
 694            (Program_Error'Identity, "potentially blocking operation");
 695       end if;
 696
 697       STPO.Write_Lock (Object.L'Access, Ceiling_Violation);
 698
 699       if Ceiling_Violation then
 700          raise Program_Error;
 701       end if;
 702
 703       Entry_Call.Mode := Timed_Call;
 704       Entry_Call.State := Now_Abortable;
 705       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 706       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 707
 708       PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);
 709       Unlock_Entry (Object);
 710
 711       --  Try to avoid waiting for completed calls.
 712       --  The call is either `Done' or not. It cannot be cancelled since there
 713       --  is no ATC construct and the timed wait has not started yet.
 714
 715       pragma Assert (Entry_Call.State /= Cancelled);
 716
 717       if Entry_Call.State = Done then
 718          Check_Exception (Self_Id, Entry_Call'Access);
 719          Entry_Call_Successful := True;
 720          return;
 721       end if;
 722
 723       if Single_Lock then
 724          STPO.Lock_RTS;
 725       else
 726          STPO.Write_Lock (Self_Id);
 727       end if;
 728
 729       Wait_For_Completion_With_Timeout (Entry_Call'Access, Timeout, Mode);
 730
 731       if Single_Lock then
 732          STPO.Unlock_RTS;
 733       else
 734          STPO.Unlock (Self_Id);
 735       end if;
 736
 737       pragma Assert (Entry_Call.State >= Done);
 738
 739       Check_Exception (Self_Id, Entry_Call'Access);
 740       Entry_Call_Successful := Entry_Call.State = Done;
 741    end Timed_Protected_Single_Entry_Call;
 742
 743    ------------------
 744    -- Unlock_Entry --
 745    ------------------
 746
 747    procedure Unlock_Entry (Object : Protection_Entry_Access) is
 748    begin
 749       --  We are exiting from a protected action, so that we decrease the
 750       --  protected object nesting level (if pragma Detect_Blocking is
 751       --  active), and remove ownership of the protected object.
 752
 753       if Detect_Blocking then
 754          declare
 755             Self_Id : constant Task_Id := Self;
 756
 757          begin
 758             --  Calls to this procedure can only take place when being within
 759             --  a protected action and when the caller is the protected
 760             --  object's owner.
 761
 762             pragma Assert (Self_Id.Common.Protected_Action_Nesting > 0
 763                              and then Object.Owner = Self_Id);
 764
 765             --  Remove ownership of the protected object
 766
 767             Object.Owner := Null_Task;
 768
 769             Self_Id.Common.Protected_Action_Nesting :=
 770               Self_Id.Common.Protected_Action_Nesting - 1;
 771          end;
 772       end if;
 773
 774       STPO.Unlock (Object.L'Access);
 775    end Unlock_Entry;
 776
 777 end System.Tasking.Protected_Objects.Single_Entry;