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------------------------------------------------------------------------------

--                                                                          --

--                GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                  --

--                                                                          --

--             SYSTEM.TASKING.PROTECTED_OBJECTS.SINGLE_ENTRY                --

--                                                                          --

--                                B o d y                                   --

--                                                                          --

--         Copyright (C) 1998-2009, Free Software Foundation, Inc.          --

--                                                                          --

-- GNARL is free software; you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNARL was developed by the GNARL team at Florida State University.       --

-- Extensive contributions were provided by Ada Core Technologies, Inc.     --

--                                                                          --

------------------------------------------------------------------------------

pragma Style_Checks (All_Checks);

--  Turn off subprogram ordering check, since restricted GNARLI subprograms are

--  gathered together at end.

--  This package provides an optimized version of Protected_Objects.Operations

--  and Protected_Objects.Entries making the following assumptions:

--    PO has only one entry

--    There is only one caller at a time (No_Entry_Queue)

--    There is no dynamic priority support (No_Dynamic_Priorities)

--    No Abort Statements

--     (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)

--    PO are at library level

--    No Requeue

--    None of the tasks will terminate (no need for finalization)

--  This interface is intended to be used in the ravenscar and restricted

--  profiles, the compiler is responsible for ensuring that the conditions

--  mentioned above are respected, except for the No_Entry_Queue restriction

--  that is checked dynamically in this package, since the check cannot be

--  performed at compile time, and is relatively cheap (see PO_Do_Or_Queue,

--  Service_Entry).

pragma Polling (Off);

--  Turn off polling, we do not want polling to take place during tasking

--  operations. It can cause  infinite loops and other problems.

pragma Suppress (All_Checks);

--  Why is this required ???

with Ada.Exceptions;

with System.Task_Primitives.Operations;

with System.Parameters;

package body System.Tasking.Protected_Objects.Single_Entry is

   package STPO renames System.Task_Primitives.Operations;

   use Parameters;

   -----------------------

   -- Local Subprograms --

   -----------------------

   procedure Send_Program_Error

     (Self_Id    : Task_Id;

      Entry_Call : Entry_Call_Link);

   pragma Inline (Send_Program_Error);

   --  Raise Program_Error in the caller of the specified entry call

   --------------------------

   -- Entry Calls Handling --

   --------------------------

   procedure Wakeup_Entry_Caller

     (Self_ID    : Task_Id;

      Entry_Call : Entry_Call_Link;

      New_State  : Entry_Call_State);

   pragma Inline (Wakeup_Entry_Caller);

   --  This is called at the end of service of an entry call,

   --  to abort the caller if he is in an abortable part, and

   --  to wake up the caller if he is on Entry_Caller_Sleep.

   --  Call it holding the lock of Entry_Call.Self.

   --

   --  Timed_Call or Simple_Call:

   --    The caller is waiting on Entry_Caller_Sleep, in

   --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.

   procedure Wait_For_Completion (Entry_Call : Entry_Call_Link);

   pragma Inline (Wait_For_Completion);

   --  This procedure suspends the calling task until the specified entry call

   --  has either been completed or cancelled. On exit, the call will not be

   --  queued. This waits for calls on protected entries.

   --  Call this only when holding Self_ID locked.

   procedure Wait_For_Completion_With_Timeout

     (Entry_Call  : Entry_Call_Link;

      Wakeup_Time : Duration;

      Mode        : Delay_Modes);

   --  Same as Wait_For_Completion but it waits for a timeout with the value

   --  specified in Wakeup_Time as well.

   procedure Check_Exception

     (Self_ID : Task_Id;

      Entry_Call : Entry_Call_Link);

   pragma Inline (Check_Exception);

   --  Raise any pending exception from the Entry_Call.

   --  This should be called at the end of every compiler interface procedure

   --  that implements an entry call.

   --  The caller should not be holding any locks, or there will be deadlock.

   procedure PO_Do_Or_Queue

     (Self_Id    : Task_Id;

      Object     : Protection_Entry_Access;

      Entry_Call : Entry_Call_Link);

   --  This procedure executes or queues an entry call, depending

   --  on the status of the corresponding barrier. It assumes that the

   --  specified object is locked.

   ---------------------

   -- Check_Exception --

   ---------------------

   procedure Check_Exception

     (Self_ID    : Task_Id;

      Entry_Call : Entry_Call_Link)

   is

      pragma Warnings (Off, Self_ID);

      procedure Internal_Raise (X : Ada.Exceptions.Exception_Id);

      pragma Import (C, Internal_Raise, "__gnat_raise_with_msg");

      use type Ada.Exceptions.Exception_Id;

      E : constant Ada.Exceptions.Exception_Id :=

            Entry_Call.Exception_To_Raise;

   begin

      if E /= Ada.Exceptions.Null_Id then

         Internal_Raise (E);

      end if;

   end Check_Exception;

   ------------------------

   -- Send_Program_Error --

   ------------------------

   procedure Send_Program_Error

     (Self_Id    : Task_Id;

      Entry_Call : Entry_Call_Link)

   is

      Caller : constant Task_Id := Entry_Call.Self;

   begin

      Entry_Call.Exception_To_Raise := Program_Error'Identity;

      if Single_Lock then

         STPO.Lock_RTS;

      end if;

      STPO.Write_Lock (Caller);

      Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);

      STPO.Unlock (Caller);

      if Single_Lock then

         STPO.Unlock_RTS;

      end if;

   end Send_Program_Error;

   -------------------------

   -- Wait_For_Completion --

   -------------------------

   procedure Wait_For_Completion (Entry_Call : Entry_Call_Link) is

      Self_Id : constant Task_Id := Entry_Call.Self;

   begin

      Self_Id.Common.State := Entry_Caller_Sleep;

      STPO.Sleep (Self_Id, Entry_Caller_Sleep);

      Self_Id.Common.State := Runnable;

   end Wait_For_Completion;

   --------------------------------------

   -- Wait_For_Completion_With_Timeout --

   --------------------------------------

   procedure Wait_For_Completion_With_Timeout

     (Entry_Call  : Entry_Call_Link;

      Wakeup_Time : Duration;

      Mode        : Delay_Modes)

   is

      Self_Id  : constant Task_Id := Entry_Call.Self;

      Timedout : Boolean;

      Yielded  : Boolean;

      pragma Unreferenced (Yielded);

      use type Ada.Exceptions.Exception_Id;

   begin

      --  This procedure waits for the entry call to be served, with a timeout.

      --  It tries to cancel the call if the timeout expires before the call is

      --  served.

      --  If we wake up from the timed sleep operation here, it may be for the

      --  following possible reasons:

      --  1) The entry call is done being served.

      --  2) The timeout has expired (Timedout = True)

      --  Once the timeout has expired we may need to continue to wait if the

      --  call is already being serviced. In that case, we want to go back to

      --  sleep, but without any timeout. The variable Timedout is used to

      --  control this. If the Timedout flag is set, we do not need to Sleep

      --  with a timeout. We just sleep until we get a wakeup for some status

      --  change.

      pragma Assert (Entry_Call.Mode = Timed_Call);

      Self_Id.Common.State := Entry_Caller_Sleep;

      STPO.Timed_Sleep

        (Self_Id, Wakeup_Time, Mode, Entry_Caller_Sleep, Timedout, Yielded);

      Entry_Call.State := (if Timedout then Cancelled else Done);

      Self_Id.Common.State := Runnable;

   end Wait_For_Completion_With_Timeout;

   -------------------------

   -- Wakeup_Entry_Caller --

   -------------------------

   --  This is called at the end of service of an entry call, to abort the

   --  caller if he is in an abortable part, and to wake up the caller if it

   --  is on Entry_Caller_Sleep. It assumes that the call is already off-queue.

   --  (This enforces the rule that a task must be off-queue if its state is

   --  Done or Cancelled.) Call it holding the lock of Entry_Call.Self.

   --  Timed_Call or Simple_Call:

   --    The caller is waiting on Entry_Caller_Sleep, in

   --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.

   --  Conditional_Call:

   --    The caller might be in Wait_For_Completion,

   --    waiting for a rendezvous (possibly requeued without abort)

   --    to complete.

   procedure Wakeup_Entry_Caller

     (Self_ID    : Task_Id;

      Entry_Call : Entry_Call_Link;

      New_State  : Entry_Call_State)

   is

      pragma Warnings (Off, Self_ID);

      Caller : constant Task_Id := Entry_Call.Self;

   begin

      pragma Assert (New_State = Done or else New_State = Cancelled);

      pragma Assert

        (Caller.Common.State /= Terminated and then

         Caller.Common.State /= Unactivated);

      Entry_Call.State := New_State;

      STPO.Wakeup (Caller, Entry_Caller_Sleep);

   end Wakeup_Entry_Caller;

   -----------------------

   -- Restricted GNARLI --

   -----------------------

   --------------------------------

   -- Complete_Single_Entry_Body --

   --------------------------------

   procedure Complete_Single_Entry_Body (Object : Protection_Entry_Access) is

      pragma Warnings (Off, Object);

   begin

      --  Nothing needs to do (Object.Call_In_Progress.Exception_To_Raise

      --  has already been set to Null_Id).

      null;

   end Complete_Single_Entry_Body;

   --------------------------------------------

   -- Exceptional_Complete_Single_Entry_Body --

   --------------------------------------------

   procedure Exceptional_Complete_Single_Entry_Body

     (Object : Protection_Entry_Access;

      Ex     : Ada.Exceptions.Exception_Id) is

   begin

      Object.Call_In_Progress.Exception_To_Raise := Ex;

   end Exceptional_Complete_Single_Entry_Body;

   ---------------------------------

   -- Initialize_Protection_Entry --

   ---------------------------------

   procedure Initialize_Protection_Entry

     (Object            : Protection_Entry_Access;

      Ceiling_Priority  : Integer;

      Compiler_Info     : System.Address;

      Entry_Body        : Entry_Body_Access)

   is

   begin

      Initialize_Protection (Object.Common'Access, Ceiling_Priority);

      Object.Compiler_Info := Compiler_Info;

      Object.Call_In_Progress := null;

      Object.Entry_Body := Entry_Body;

      Object.Entry_Queue := null;

   end Initialize_Protection_Entry;

   ----------------

   -- Lock_Entry --

   ----------------

   --  Compiler interface only.

   --  Do not call this procedure from within the run-time system.

   procedure Lock_Entry (Object : Protection_Entry_Access) is

   begin

      Lock (Object.Common'Access);

   end Lock_Entry;

   --------------------------

   -- Lock_Read_Only_Entry --

   --------------------------

   --  Compiler interface only

   --  Do not call this procedure from within the runtime system

   procedure Lock_Read_Only_Entry (Object : Protection_Entry_Access) is

   begin

      Lock_Read_Only (Object.Common'Access);

   end Lock_Read_Only_Entry;

   --------------------

   -- PO_Do_Or_Queue --

   --------------------

   procedure PO_Do_Or_Queue

     (Self_Id    : Task_Id;

      Object     : Protection_Entry_Access;

      Entry_Call : Entry_Call_Link)

   is

      Barrier_Value : Boolean;

   begin

      --  When the Action procedure for an entry body returns, it must be

      --  completed (having called [Exceptional_]Complete_Entry_Body).

      Barrier_Value := Object.Entry_Body.Barrier (Object.Compiler_Info, 1);

      if Barrier_Value then

         if Object.Call_In_Progress /= null then

            --  This violates the No_Entry_Queue restriction, send

            --  Program_Error to the caller.

            Send_Program_Error (Self_Id, Entry_Call);

            return;

         end if;

         Object.Call_In_Progress := Entry_Call;

         Object.Entry_Body.Action

           (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);

         Object.Call_In_Progress := null;

         if Single_Lock then

            STPO.Lock_RTS;

         end if;

         STPO.Write_Lock (Entry_Call.Self);

         Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);

         STPO.Unlock (Entry_Call.Self);

         if Single_Lock then

            STPO.Unlock_RTS;

         end if;

      elsif Entry_Call.Mode /= Conditional_Call then

         if Object.Entry_Queue /= null then

            --  This violates the No_Entry_Queue restriction, send

            --  Program_Error to the caller.

            Send_Program_Error (Self_Id, Entry_Call);

            return;

         else

            Object.Entry_Queue := Entry_Call;

         end if;

      else

         --  Conditional_Call

         if Single_Lock then

            STPO.Lock_RTS;

         end if;

         STPO.Write_Lock (Entry_Call.Self);

         Wakeup_Entry_Caller (Self_Id, Entry_Call, Cancelled);

         STPO.Unlock (Entry_Call.Self);

         if Single_Lock then

            STPO.Unlock_RTS;

         end if;

      end if;

   exception

      when others =>

         Send_Program_Error

           (Self_Id, Entry_Call);

   end PO_Do_Or_Queue;

   ----------------------------

   -- Protected_Single_Count --

   ----------------------------

   function Protected_Count_Entry (Object : Protection_Entry) return Natural is

   begin

      if Object.Entry_Queue /= null then

         return 1;

      else

         return 0;

      end if;

   end Protected_Count_Entry;

   ---------------------------------

   -- Protected_Single_Entry_Call --

   ---------------------------------

   procedure Protected_Single_Entry_Call

     (Object             : Protection_Entry_Access;

      Uninterpreted_Data : System.Address;

      Mode               : Call_Modes)

   is

      Self_Id    : constant Task_Id := STPO.Self;

      Entry_Call : Entry_Call_Record renames Self_Id.Entry_Calls (1);

   begin

      --  If pragma Detect_Blocking is active then Program_Error must be

      --  raised if this potentially blocking operation is called from a

      --  protected action.

      if Detect_Blocking

        and then Self_Id.Common.Protected_Action_Nesting > 0

      then

         raise Program_Error with "potentially blocking operation";

      end if;

      Lock_Entry (Object);

      Entry_Call.Mode := Mode;

      Entry_Call.State := Now_Abortable;

      Entry_Call.Uninterpreted_Data := Uninterpreted_Data;

      Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;

      PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);

      Unlock_Entry (Object);

      --  The call is either `Done' or not. It cannot be cancelled since there

      --  is no ATC construct.

      pragma Assert (Entry_Call.State /= Cancelled);

      if Entry_Call.State /= Done then

         if Single_Lock then

            STPO.Lock_RTS;

         end if;

         STPO.Write_Lock (Self_Id);

         Wait_For_Completion (Entry_Call'Access);

         STPO.Unlock (Self_Id);

         if Single_Lock then

            STPO.Unlock_RTS;

         end if;

      end if;

      Check_Exception (Self_Id, Entry_Call'Access);

   end Protected_Single_Entry_Call;

   -----------------------------------

   -- Protected_Single_Entry_Caller --

   -----------------------------------

   function Protected_Single_Entry_Caller

     (Object : Protection_Entry) return Task_Id is

   begin

      return Object.Call_In_Progress.Self;

   end Protected_Single_Entry_Caller;

   -------------------

   -- Service_Entry --

   -------------------

   procedure Service_Entry (Object : Protection_Entry_Access) is

      Self_Id    : constant Task_Id := STPO.Self;

      Entry_Call : constant Entry_Call_Link := Object.Entry_Queue;

      Caller     : Task_Id;

   begin

      if Entry_Call /= null

        and then Object.Entry_Body.Barrier (Object.Compiler_Info, 1)

      then

         Object.Entry_Queue := null;

         if Object.Call_In_Progress /= null then

            --  Violation of No_Entry_Queue restriction, raise exception

            Send_Program_Error (Self_Id, Entry_Call);

            Unlock_Entry (Object);

            return;

         end if;

         Object.Call_In_Progress := Entry_Call;

         Object.Entry_Body.Action

           (Object.Compiler_Info, Entry_Call.Uninterpreted_Data, 1);

         Object.Call_In_Progress := null;

         Caller := Entry_Call.Self;

         Unlock_Entry (Object);

         if Single_Lock then

            STPO.Lock_RTS;

         end if;

         STPO.Write_Lock (Caller);

         Wakeup_Entry_Caller (Self_Id, Entry_Call, Done);

         STPO.Unlock (Caller);

         if Single_Lock then

            STPO.Unlock_RTS;

         end if;

      else

         --  Just unlock the entry

         Unlock_Entry (Object);

      end if;

   exception

      when others =>

         Send_Program_Error (Self_Id, Entry_Call);

         Unlock_Entry (Object);

   end Service_Entry;

   ---------------------------------------

   -- Timed_Protected_Single_Entry_Call --

   ---------------------------------------

   --  Compiler interface only (do not call from within the RTS)

   procedure Timed_Protected_Single_Entry_Call

     (Object                : Protection_Entry_Access;

      Uninterpreted_Data    : System.Address;

      Timeout               : Duration;

      Mode                  : Delay_Modes;

      Entry_Call_Successful : out Boolean)

   is

      Self_Id           : constant Task_Id  := STPO.Self;

      Entry_Call        : Entry_Call_Record renames Self_Id.Entry_Calls (1);

   begin

      --  If pragma Detect_Blocking is active then Program_Error must be

      --  raised if this potentially blocking operation is called from a

      --  protected action.

      if Detect_Blocking

        and then Self_Id.Common.Protected_Action_Nesting > 0

      then

         raise Program_Error with "potentially blocking operation";

      end if;

      Lock (Object.Common'Access);

      Entry_Call.Mode := Timed_Call;

      Entry_Call.State := Now_Abortable;

      Entry_Call.Uninterpreted_Data := Uninterpreted_Data;

      Entry_Call.Exception_To_Raise := Ada.Exceptions.Null_Id;

      PO_Do_Or_Queue (Self_Id, Object, Entry_Call'Access);

      Unlock_Entry (Object);

      --  Try to avoid waiting for completed calls.

      --  The call is either `Done' or not. It cannot be cancelled since there

      --  is no ATC construct and the timed wait has not started yet.

      pragma Assert (Entry_Call.State /= Cancelled);

      if Entry_Call.State = Done then

         Check_Exception (Self_Id, Entry_Call'Access);

         Entry_Call_Successful := True;

         return;

      end if;

      if Single_Lock then

         STPO.Lock_RTS;

      else

         STPO.Write_Lock (Self_Id);

      end if;

      Wait_For_Completion_With_Timeout (Entry_Call'Access, Timeout, Mode);

      if Single_Lock then

         STPO.Unlock_RTS;

      else

         STPO.Unlock (Self_Id);

      end if;

      pragma Assert (Entry_Call.State >= Done);

      Check_Exception (Self_Id, Entry_Call'Access);

      Entry_Call_Successful := Entry_Call.State = Done;

   end Timed_Protected_Single_Entry_Call;

   ------------------

   -- Unlock_Entry --

   ------------------

   procedure Unlock_Entry (Object : Protection_Entry_Access) is

   begin

      Unlock (Object.Common'Access);

   end Unlock_Entry;

end System.Tasking.Protected_Objects.Single_Entry;