gcc/ada/libgnarl/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) 1998-2020, 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 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNARL was developed by the GNARL team at Florida State University.       --
  28 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 pragma Style_Checks (All_Checks);
  33 --  Turn off subprogram ordering check, since restricted GNARLI subprograms are
  34 --  gathered together at end.
  35
  36 --  This package provides an optimized version of Protected_Objects.Operations
  37 --  and Protected_Objects.Entries making the following assumptions:
  38
  39 --    PO has only one entry
  40 --    There is only one caller at a time (No_Entry_Queue)
  41 --    There is no dynamic priority support (No_Dynamic_Priorities)
  42 --    No Abort Statements
  43 --     (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)
  44 --    PO are at library level
  45 --    No Requeue
  46 --    None of the tasks will terminate (no need for finalization)
  47
  48 --  This interface is intended to be used in the ravenscar and restricted
  49 --  profiles, the compiler is responsible for ensuring that the conditions
  50 --  mentioned above are respected, except for the No_Entry_Queue restriction
  51 --  that is checked dynamically in this package, since the check cannot be
  52 --  performed at compile time, and is relatively cheap (see PO_Do_Or_Queue,
  53 --  Service_Entry).
  54
  55 pragma Polling (Off);
  56 --  Turn off polling, we do not want polling to take place during tasking
  57 --  operations. It can cause infinite loops and other problems.
  58
  59 pragma Suppress (All_Checks);
  60 --  Why is this required ???
  61
  62 with Ada.Exceptions;
  63
  64 with System.Task_Primitives.Operations;
  65 with System.Parameters;
  66
  67 package body System.Tasking.Protected_Objects.Single_Entry is
  68
  69    package STPO renames System.Task_Primitives.Operations;
  70
  71    use Parameters;
  72
  73    -----------------------
  74    -- Local Subprograms --
  75    -----------------------
  76
  77    procedure Send_Program_Error (Entry_Call : Entry_Call_Link);
  78    pragma Inline (Send_Program_Error);
  79    --  Raise Program_Error in the caller of the specified entry call
  80
  81    --------------------------
  82    -- Entry Calls Handling --
  83    --------------------------
  84
  85    procedure Wakeup_Entry_Caller (Entry_Call : Entry_Call_Link);
  86    pragma Inline (Wakeup_Entry_Caller);
  87    --  This is called at the end of service of an entry call, to abort the
  88    --  caller if he is in an abortable part, and to wake up the caller if he
  89    --  is on Entry_Caller_Sleep. Call it holding the lock of Entry_Call.Self.
  90
  91    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link);
  92    pragma Inline (Wait_For_Completion);
  93    --  This procedure suspends the calling task until the specified entry call
  94    --  has either been completed or cancelled. On exit, the call will not be
  95    --  queued. This waits for calls on protected entries.
  96    --  Call this only when holding Self_ID locked.
  97
  98    procedure Check_Exception
  99      (Self_ID : Task_Id;
 100       Entry_Call : Entry_Call_Link);
 101    pragma Inline (Check_Exception);
 102    --  Raise any pending exception from the Entry_Call. This should be called
 103    --  at the end of every compiler interface procedure that implements an
 104    --  entry call. The caller should not be holding any locks, or there will
 105    --  be deadlock.
 106
 107    procedure PO_Do_Or_Queue
 108      (Object     : Protection_Entry_Access;
 109       Entry_Call : Entry_Call_Link);
 110    --  This procedure executes or queues an entry call, depending on the status
 111    --  of the corresponding barrier. The specified object is assumed locked.
 112
 113    ---------------------
 114    -- Check_Exception --
 115    ---------------------
 116
 117    procedure Check_Exception
 118      (Self_ID    : Task_Id;
 119       Entry_Call : Entry_Call_Link)
 120    is
 121       pragma Warnings (Off, Self_ID);
 122
 123       procedure Internal_Raise (X : Ada.Exceptions.Exception_Id);
 124       pragma Import (C, Internal_Raise, "__gnat_raise_with_msg");
 125
 126       use type Ada.Exceptions.Exception_Id;
 127
 128       E : constant Ada.Exceptions.Exception_Id :=
 129             Entry_Call.Exception_To_Raise;
 130
 131    begin
 132       if E /= Ada.Exceptions.Null_Id then
 133          Internal_Raise (E);
 134       end if;
 135    end Check_Exception;
 136
 137    ------------------------
 138    -- Send_Program_Error --
 139    ------------------------
 140
 141    procedure Send_Program_Error (Entry_Call : Entry_Call_Link) is
 142       Caller : constant Task_Id := Entry_Call.Self;
 143
 144    begin
 145       Entry_Call.Exception_To_Raise := Program_Error'Identity;
 146
 147       if Single_Lock then
 148          STPO.Lock_RTS;
 149       end if;
 150
 151       STPO.Write_Lock (Caller);
 152       Wakeup_Entry_Caller (Entry_Call);
 153       STPO.Unlock (Caller);
 154
 155       if Single_Lock then
 156          STPO.Unlock_RTS;
 157       end if;
 158    end Send_Program_Error;
 159
 160    -------------------------
 161    -- Wait_For_Completion --
 162    -------------------------
 163
 164    procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is
 165       Self_Id : constant Task_Id := Entry_Call.Self;
 166    begin
 167       Self_Id.Common.State := Entry_Caller_Sleep;
 168       STPO.Sleep (Self_Id, Entry_Caller_Sleep);
 169       Self_Id.Common.State := Runnable;
 170    end Wait_For_Completion;
 171
 172    -------------------------
 173    -- Wakeup_Entry_Caller --
 174    -------------------------
 175
 176    --  This is called at the end of service of an entry call, to abort the
 177    --  caller if he is in an abortable part, and to wake up the caller if it
 178    --  is on Entry_Caller_Sleep. It assumes that the call is already off-queue.
 179
 180    --  (This enforces the rule that a task must be off-queue if its state is
 181    --  Done or Cancelled.) Call it holding the lock of Entry_Call.Self.
 182
 183    --  The caller is waiting on Entry_Caller_Sleep, in Wait_For_Completion.
 184
 185    procedure Wakeup_Entry_Caller
 186      (Entry_Call : Entry_Call_Link)
 187    is
 188       Caller : constant Task_Id := Entry_Call.Self;
 189    begin
 190       pragma Assert
 191         (Caller.Common.State /= Terminated and then
 192          Caller.Common.State /= Unactivated);
 193       Entry_Call.State := Done;
 194       STPO.Wakeup (Caller, Entry_Caller_Sleep);
 195    end Wakeup_Entry_Caller;
 196
 197    -----------------------
 198    -- Restricted GNARLI --
 199    -----------------------
 200
 201    --------------------------------------------
 202    -- Exceptional_Complete_Single_Entry_Body --
 203    --------------------------------------------
 204
 205    procedure Exceptional_Complete_Single_Entry_Body
 206      (Object : Protection_Entry_Access;
 207       Ex     : Ada.Exceptions.Exception_Id)
 208    is
 209    begin
 210       Object.Call_In_Progress.Exception_To_Raise := Ex;
 211    end Exceptional_Complete_Single_Entry_Body;
 212
 213    ---------------------------------
 214    -- Initialize_Protection_Entry --
 215    ---------------------------------
 216
 217    procedure Initialize_Protection_Entry
 218      (Object           : Protection_Entry_Access;
 219       Ceiling_Priority : Integer;
 220       Compiler_Info    : System.Address;
 221       Entry_Body       : Entry_Body_Access)
 222    is
 223    begin
 224       Initialize_Protection (Object.Common'Access, Ceiling_Priority);
 225
 226       Object.Compiler_Info := Compiler_Info;
 227       Object.Call_In_Progress := null;
 228       Object.Entry_Body := Entry_Body;
 229       Object.Entry_Queue := null;
 230    end Initialize_Protection_Entry;
 231
 232    ----------------
 233    -- Lock_Entry --
 234    ----------------
 235
 236    --  Compiler interface only
 237
 238    --  Do not call this procedure from within the run-time system.
 239
 240    procedure Lock_Entry (Object : Protection_Entry_Access) is
 241    begin
 242       Lock (Object.Common'Access);
 243    end Lock_Entry;
 244
 245    --------------------------
 246    -- Lock_Read_Only_Entry --
 247    --------------------------
 248
 249    --  Compiler interface only
 250
 251    --  Do not call this procedure from within the runtime system
 252
 253    procedure Lock_Read_Only_Entry (Object : Protection_Entry_Access) is
 254    begin
 255       Lock_Read_Only (Object.Common'Access);
 256    end Lock_Read_Only_Entry;
 257
 258    --------------------
 259    -- PO_Do_Or_Queue --
 260    --------------------
 261
 262    procedure PO_Do_Or_Queue
 263      (Object     : Protection_Entry_Access;
 264       Entry_Call : Entry_Call_Link)
 265    is
 266       Barrier_Value : Boolean;
 267
 268    begin
 269       --  When the Action procedure for an entry body returns, it must be
 270       --  completed (having called [Exceptional_]Complete_Entry_Body).
 271
 272       Barrier_Value := Object.Entry_Body.Barrier (Object.Compiler_Info, 1);
 273
 274       if Barrier_Value then
 275          if Object.Call_In_Progress /= null then
 276
 277             --  This violates the No_Entry_Queue restriction, send
 278             --  Program_Error to the caller.
 279
 280             Send_Program_Error (Entry_Call);
 281             return;
 282          end if;
 283
 284          Object.Call_In_Progress := Entry_Call;
 285          Object.Entry_Body.Action
 286            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 287          Object.Call_In_Progress := null;
 288
 289          if Single_Lock then
 290             STPO.Lock_RTS;
 291          end if;
 292
 293          STPO.Write_Lock (Entry_Call.Self);
 294          Wakeup_Entry_Caller (Entry_Call);
 295          STPO.Unlock (Entry_Call.Self);
 296
 297          if Single_Lock then
 298             STPO.Unlock_RTS;
 299          end if;
 300
 301       else
 302          pragma Assert (Entry_Call.Mode = Simple_Call);
 303
 304          if Object.Entry_Queue /= null then
 305
 306             --  This violates the No_Entry_Queue restriction, send
 307             --  Program_Error to the caller.
 308
 309             Send_Program_Error (Entry_Call);
 310             return;
 311          else
 312             Object.Entry_Queue := Entry_Call;
 313          end if;
 314
 315       end if;
 316
 317    exception
 318       when others =>
 319          Send_Program_Error (Entry_Call);
 320    end PO_Do_Or_Queue;
 321
 322    ---------------------------
 323    -- Protected_Count_Entry --
 324    ---------------------------
 325
 326    function Protected_Count_Entry (Object : Protection_Entry) return Natural is
 327    begin
 328       if Object.Entry_Queue /= null then
 329          return 1;
 330       else
 331          return 0;
 332       end if;
 333    end Protected_Count_Entry;
 334
 335    ---------------------------------
 336    -- Protected_Single_Entry_Call --
 337    ---------------------------------
 338
 339    procedure Protected_Single_Entry_Call
 340      (Object             : Protection_Entry_Access;
 341       Uninterpreted_Data : System.Address)
 342    is
 343       Self_Id    : constant Task_Id := STPO.Self;
 344       Entry_Call : Entry_Call_Record renames
 345         Self_Id.Entry_Calls (Self_Id.Entry_Calls'First);
 346    begin
 347       --  If pragma Detect_Blocking is active then Program_Error must be
 348       --  raised if this potentially blocking operation is called from a
 349       --  protected action.
 350
 351       if Detect_Blocking
 352         and then Self_Id.Common.Protected_Action_Nesting > 0
 353       then
 354          raise Program_Error with "potentially blocking operation";
 355       end if;
 356
 357       Lock_Entry (Object);
 358
 359       Entry_Call.Mode := Simple_Call;
 360       Entry_Call.State := Now_Abortable;
 361       Entry_Call.Uninterpreted_Data := Uninterpreted_Data;
 362       Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;
 363
 364       PO_Do_Or_Queue (Object, Entry_Call'Access);
 365       Unlock_Entry (Object);
 366
 367       --  The call is either `Done' or not. It cannot be cancelled since there
 368       --  is no ATC construct.
 369
 370       pragma Assert (Entry_Call.State /= Cancelled);
 371
 372       if Entry_Call.State /= Done then
 373          if Single_Lock then
 374             STPO.Lock_RTS;
 375          end if;
 376
 377          STPO.Write_Lock (Self_Id);
 378          Wait_For_Completion (Entry_Call'Access);
 379          STPO.Unlock (Self_Id);
 380
 381          if Single_Lock then
 382             STPO.Unlock_RTS;
 383          end if;
 384       end if;
 385
 386       Check_Exception (Self_Id, Entry_Call'Access);
 387    end Protected_Single_Entry_Call;
 388
 389    -----------------------------------
 390    -- Protected_Single_Entry_Caller --
 391    -----------------------------------
 392
 393    function Protected_Single_Entry_Caller
 394      (Object : Protection_Entry) return Task_Id
 395    is
 396    begin
 397       return Object.Call_In_Progress.Self;
 398    end Protected_Single_Entry_Caller;
 399
 400    -------------------
 401    -- Service_Entry --
 402    -------------------
 403
 404    procedure Service_Entry (Object : Protection_Entry_Access) is
 405       Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;
 406       Caller     : Task_Id;
 407
 408    begin
 409       if Entry_Call /= null
 410         and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)
 411       then
 412          Object.Entry_Queue := null;
 413
 414          if Object.Call_In_Progress /= null then
 415
 416             --  Violation of No_Entry_Queue restriction, raise exception
 417
 418             Send_Program_Error (Entry_Call);
 419             Unlock_Entry (Object);
 420             return;
 421          end if;
 422
 423          Object.Call_In_Progress := Entry_Call;
 424          Object.Entry_Body.Action
 425            (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);
 426          Object.Call_In_Progress := null;
 427          Caller := Entry_Call.Self;
 428          Unlock_Entry (Object);
 429
 430          if Single_Lock then
 431             STPO.Lock_RTS;
 432          end if;
 433
 434          STPO.Write_Lock (Caller);
 435          Wakeup_Entry_Caller (Entry_Call);
 436          STPO.Unlock (Caller);
 437
 438          if Single_Lock then
 439             STPO.Unlock_RTS;
 440          end if;
 441
 442       else
 443          --  Just unlock the entry
 444
 445          Unlock_Entry (Object);
 446       end if;
 447
 448    exception
 449       when others =>
 450          Send_Program_Error (Entry_Call);
 451          Unlock_Entry (Object);
 452    end Service_Entry;
 453
 454    ------------------
 455    -- Unlock_Entry --
 456    ------------------
 457
 458    procedure Unlock_Entry (Object : Protection_Entry_Access) is
 459    begin
 460       Unlock (Object.Common'Access);
 461    end Unlock_Entry;
 462
 463 end System.Tasking.Protected_Objects.Single_Entry;