------------------------------------------------------------------------------
--                                                                          --
--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
--                                                                          --
--                     S Y S T E M . I N T E R R U P T S                    --
--                                                                          --
--                                  B o d y                                 --
--                                                                          --
--         Copyright (C) 1992-2008, 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 2,  or (at your option) any later ver- --
-- sion. GNARL 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.  See the GNU General Public License --
-- for  more details.  You should have  received  a copy of the GNU General --
-- Public License  distributed with GNARL; see file COPYING.  If not, write --
-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
-- Boston, MA 02110-1301, USA.                                              --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
--                                                                          --
-- GNARL was developed by the GNARL team at Florida State University.       --
-- Extensive contributions were provided by Ada Core Technologies, Inc.     --
--                                                                          --
------------------------------------------------------------------------------

--  Invariants:

--  All user-handleable interrupts are masked at all times in all
--  tasks/threads except possibly for the Interrupt_Manager task.

--  When a user task wants to have the effect of masking/unmasking an
--  interrupt, it must call Block_Interrupt/Unblock_Interrupt, which
--  will have the effect of unmasking/masking the interrupt in the
--  Interrupt_Manager task.

--  Note : Direct calls to sigaction, sigprocmask, pthread_sigsetmask or any
--  other low-level interface that changes the interrupt action or
--  interrupt mask needs a careful thought.
--  One may achieve the effect of system calls first masking RTS blocked
--  (by calling Block_Interrupt) for the interrupt under consideration.
--  This will make all the tasks in RTS blocked for the Interrupt.

--  Once we associate a Server_Task with an interrupt, the task never
--  goes away, and we never remove the association.

--  There is no more than one interrupt per Server_Task and no more than
--  one Server_Task per interrupt.

with Ada.Task_Identification;

with System.Task_Primitives;
with System.Interrupt_Management;

with System.Interrupt_Management.Operations;
pragma Elaborate_All (System.Interrupt_Management.Operations);

with System.Task_Primitives.Operations;
with System.Task_Primitives.Interrupt_Operations;
with System.Storage_Elements;
with System.Tasking.Utilities;

with System.Tasking.Rendezvous;
pragma Elaborate_All (System.Tasking.Rendezvous);

with System.Tasking.Initialization;
with System.Parameters;

with Ada.Unchecked_Conversion;

package body System.Interrupts is

   use Parameters;
   use Tasking;

   package POP renames System.Task_Primitives.Operations;
   package PIO renames System.Task_Primitives.Interrupt_Operations;
   package IMNG renames System.Interrupt_Management;
   package IMOP renames System.Interrupt_Management.Operations;

   function To_System is new Ada.Unchecked_Conversion
     (Ada.Task_Identification.Task_Id, Task_Id);

   -----------------
   -- Local Tasks --
   -----------------

   --  WARNING: System.Tasking.Stages performs calls to this task with
   --  low-level constructs. Do not change this spec without synchronizing it.

   task Interrupt_Manager is
      entry Detach_Interrupt_Entries (T : Task_Id);

      entry Initialize (Mask : IMNG.Interrupt_Mask);

      entry Attach_Handler
        (New_Handler : Parameterless_Handler;
         Interrupt   : Interrupt_ID;
         Static      : Boolean;
         Restoration : Boolean := False);

      entry Exchange_Handler
        (Old_Handler : out Parameterless_Handler;
         New_Handler : Parameterless_Handler;
         Interrupt   : Interrupt_ID;
         Static      : Boolean);

      entry Detach_Handler
        (Interrupt   : Interrupt_ID;
         Static      : Boolean);

      entry Bind_Interrupt_To_Entry
        (T         : Task_Id;
         E         : Task_Entry_Index;
         Interrupt : Interrupt_ID);

      entry Block_Interrupt (Interrupt : Interrupt_ID);

      entry Unblock_Interrupt (Interrupt : Interrupt_ID);

      entry Ignore_Interrupt (Interrupt : Interrupt_ID);

      entry Unignore_Interrupt (Interrupt : Interrupt_ID);

      pragma Interrupt_Priority (System.Interrupt_Priority'Last);
   end Interrupt_Manager;

   task type Server_Task (Interrupt : Interrupt_ID) is
      pragma Priority (System.Interrupt_Priority'Last);
      --  Note: the above pragma Priority is strictly speaking improper since
      --  it is outside the range of allowed priorities, but the compiler
      --  treats system units specially and does not apply this range checking
      --  rule to system units.

   end Server_Task;

   type Server_Task_Access is access Server_Task;

   -------------------------------
   -- Local Types and Variables --
   -------------------------------

   type Entry_Assoc is record
      T : Task_Id;
      E : Task_Entry_Index;
   end record;

   type Handler_Assoc is record
      H      : Parameterless_Handler;
      Static : Boolean;   --  Indicates static binding;
   end record;

   User_Handler : array (Interrupt_ID'Range) of Handler_Assoc :=
                    (others => (null, Static => False));
   pragma Volatile_Components (User_Handler);
   --  Holds the protected procedure handler (if any) and its Static
   --  information for each interrupt. A handler is a Static one if it is
   --  specified through the pragma Attach_Handler. Attach_Handler. Otherwise,
   --  not static)

   User_Entry : array (Interrupt_ID'Range) of Entry_Assoc :=
                  (others => (T => Null_Task, E => Null_Task_Entry));
   pragma Volatile_Components (User_Entry);
   --  Holds the task and entry index (if any) for each interrupt

   Blocked : array (Interrupt_ID'Range) of Boolean := (others => False);
   pragma Atomic_Components (Blocked);
   --  True iff the corresponding interrupt is blocked in the process level

   Ignored : array (Interrupt_ID'Range) of Boolean := (others => False);
   pragma Atomic_Components (Ignored);
   --  True iff the corresponding interrupt is blocked in the process level

   Last_Unblocker :
     array (Interrupt_ID'Range) of Task_Id := (others => Null_Task);
   pragma Atomic_Components (Last_Unblocker);
   --  Holds the ID of the last Task which Unblocked this Interrupt. It
   --  contains Null_Task if no tasks have ever requested the Unblocking
   --  operation or the Interrupt is currently Blocked.

   Server_ID : array (Interrupt_ID'Range) of Task_Id :=
                 (others => Null_Task);
   pragma Atomic_Components (Server_ID);
   --  Holds the Task_Id of the Server_Task for each interrupt. Task_Id is
   --  needed to accomplish locking per Interrupt base. Also is needed to
   --  decide whether to create a new Server_Task.

   --  Type and Head, Tail of the list containing Registered Interrupt
   --  Handlers. These definitions are used to register the handlers
   --  specified by the pragma Interrupt_Handler.

   type Registered_Handler;
   type R_Link is access all Registered_Handler;

   type Registered_Handler is record
      H    : System.Address := System.Null_Address;
      Next : R_Link := null;
   end record;

   Registered_Handler_Head : R_Link := null;
   Registered_Handler_Tail : R_Link := null;

   Access_Hold : Server_Task_Access;
   --  Variable used to allocate Server_Task using "new"

   -----------------------
   -- Local Subprograms --
   -----------------------

   function Is_Registered (Handler : Parameterless_Handler) return Boolean;
   --  See if the Handler has been "pragma"ed using Interrupt_Handler. Always
   --  consider a null handler as registered.

   --------------------
   -- Attach_Handler --
   --------------------

   --  Calling this procedure with New_Handler = null and Static = True means
   --  we want to detach the current handler regardless of the previous
   --  handler's binding status (i.e. do not care if it is a dynamic or static
   --  handler).

   --  This option is needed so that during the finalization of a PO, we can
   --  detach handlers attached through pragma Attach_Handler.

   procedure Attach_Handler
     (New_Handler : Parameterless_Handler;
      Interrupt   : Interrupt_ID;
      Static      : Boolean := False)
   is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Attach_Handler (New_Handler, Interrupt, Static);

   end Attach_Handler;

   -----------------------------
   -- Bind_Interrupt_To_Entry --
   -----------------------------

   --  This procedure raises a Program_Error if it tries to bind an interrupt
   --  to which an Entry or a Procedure is already bound.

   procedure Bind_Interrupt_To_Entry
     (T       : Task_Id;
      E       : Task_Entry_Index;
      Int_Ref : System.Address)
   is
      Interrupt   : constant Interrupt_ID :=
                      Interrupt_ID (Storage_Elements.To_Integer (Int_Ref));

   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Bind_Interrupt_To_Entry (T, E, Interrupt);
   end Bind_Interrupt_To_Entry;

   ---------------------
   -- Block_Interrupt --
   ---------------------

   procedure Block_Interrupt (Interrupt : Interrupt_ID) is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Block_Interrupt (Interrupt);
   end Block_Interrupt;

   ---------------------
   -- Current_Handler --
   ---------------------

   function Current_Handler
     (Interrupt : Interrupt_ID) return Parameterless_Handler
   is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      --  ??? Since Parameterless_Handler is not Atomic, the current
      --  implementation is wrong. We need a new service in Interrupt_Manager
      --  to ensure atomicity.

      return User_Handler (Interrupt).H;
   end Current_Handler;

   --------------------
   -- Detach_Handler --
   --------------------

   --  Calling this procedure with Static = True means we want to Detach the
   --  current handler regardless of the previous handler's binding status
   --  (i.e. do not care if it is a dynamic or static handler).

   --  This option is needed so that during the finalization of a PO, we can
   --  detach handlers attached through pragma Attach_Handler.

   procedure Detach_Handler
     (Interrupt : Interrupt_ID;
      Static    : Boolean := False)
   is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Detach_Handler (Interrupt, Static);
   end Detach_Handler;

   ------------------------------
   -- Detach_Interrupt_Entries --
   ------------------------------

   procedure Detach_Interrupt_Entries (T : Task_Id) is
   begin
      Interrupt_Manager.Detach_Interrupt_Entries (T);
   end Detach_Interrupt_Entries;

   ----------------------
   -- Exchange_Handler --
   ----------------------

   --  Calling this procedure with New_Handler = null and Static = True means
   --  we want to detach the current handler regardless of the previous
   --  handler's binding status (i.e. do not care if it is a dynamic or static
   --  handler).

   --  This option is needed so that during the finalization of a PO, we can
   --  detach handlers attached through pragma Attach_Handler.

   procedure Exchange_Handler
     (Old_Handler : out Parameterless_Handler;
      New_Handler : Parameterless_Handler;
      Interrupt   : Interrupt_ID;
      Static      : Boolean := False)
   is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Exchange_Handler
        (Old_Handler, New_Handler, Interrupt, Static);
   end Exchange_Handler;

   --------------
   -- Finalize --
   --------------

   procedure Finalize (Object : in out Static_Interrupt_Protection) is
   begin
      --  ??? loop to be executed only when we're not doing library level
      --  finalization, since in this case all interrupt tasks are gone.

      if not Interrupt_Manager'Terminated then
         for N in reverse Object.Previous_Handlers'Range loop
            Interrupt_Manager.Attach_Handler
              (New_Handler => Object.Previous_Handlers (N).Handler,
               Interrupt   => Object.Previous_Handlers (N).Interrupt,
               Static      => Object.Previous_Handlers (N).Static,
               Restoration => True);
         end loop;
      end if;

      Tasking.Protected_Objects.Entries.Finalize
        (Tasking.Protected_Objects.Entries.Protection_Entries (Object));
   end Finalize;

   -------------------------------------
   -- Has_Interrupt_Or_Attach_Handler --
   -------------------------------------

   --  Need comments as to why these always return True ???

   function Has_Interrupt_Or_Attach_Handler
     (Object : access Dynamic_Interrupt_Protection) return Boolean
   is
      pragma Unreferenced (Object);
   begin
      return True;
   end Has_Interrupt_Or_Attach_Handler;

   function Has_Interrupt_Or_Attach_Handler
     (Object : access Static_Interrupt_Protection) return Boolean
   is
      pragma Unreferenced (Object);
   begin
      return True;
   end Has_Interrupt_Or_Attach_Handler;

   ----------------------
   -- Ignore_Interrupt --
   ----------------------

   procedure Ignore_Interrupt (Interrupt : Interrupt_ID) is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Ignore_Interrupt (Interrupt);
   end Ignore_Interrupt;

   ----------------------
   -- Install_Handlers --
   ----------------------

   procedure Install_Handlers
     (Object       : access Static_Interrupt_Protection;
      New_Handlers : New_Handler_Array)
   is
   begin
      for N in New_Handlers'Range loop

         --  We need a lock around this ???

         Object.Previous_Handlers (N).Interrupt := New_Handlers (N).Interrupt;
         Object.Previous_Handlers (N).Static    := User_Handler
           (New_Handlers (N).Interrupt).Static;

         --  We call Exchange_Handler and not directly Interrupt_Manager.
         --  Exchange_Handler so we get the Is_Reserved check.

         Exchange_Handler
           (Old_Handler => Object.Previous_Handlers (N).Handler,
            New_Handler => New_Handlers (N).Handler,
            Interrupt   => New_Handlers (N).Interrupt,
            Static      => True);
      end loop;
   end Install_Handlers;

   ---------------------------------
   -- Install_Restricted_Handlers --
   ---------------------------------

   procedure Install_Restricted_Handlers (Handlers : New_Handler_Array) is
   begin
      for N in Handlers'Range loop
         Attach_Handler (Handlers (N).Handler, Handlers (N).Interrupt, True);
      end loop;
   end Install_Restricted_Handlers;

   ----------------
   -- Is_Blocked --
   ----------------

   function Is_Blocked (Interrupt : Interrupt_ID) return Boolean is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return Blocked (Interrupt);
   end Is_Blocked;

   -----------------------
   -- Is_Entry_Attached --
   -----------------------

   function Is_Entry_Attached (Interrupt : Interrupt_ID) return Boolean is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return User_Entry (Interrupt).T /= Null_Task;
   end Is_Entry_Attached;

   -------------------------
   -- Is_Handler_Attached --
   -------------------------

   function Is_Handler_Attached (Interrupt : Interrupt_ID) return Boolean is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return User_Handler (Interrupt).H /= null;
   end Is_Handler_Attached;

   ----------------
   -- Is_Ignored --
   ----------------

   function Is_Ignored (Interrupt : Interrupt_ID) return Boolean is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return Ignored (Interrupt);
   end Is_Ignored;

   -------------------
   -- Is_Registered --
   -------------------

   function Is_Registered (Handler : Parameterless_Handler) return Boolean is

      type Fat_Ptr is record
         Object_Addr  : System.Address;
         Handler_Addr : System.Address;
      end record;

      function To_Fat_Ptr is new Ada.Unchecked_Conversion
        (Parameterless_Handler, Fat_Ptr);

      Ptr : R_Link;
      Fat : Fat_Ptr;

   begin
      if Handler = null then
         return True;
      end if;

      Fat := To_Fat_Ptr (Handler);

      Ptr := Registered_Handler_Head;

      while Ptr /= null loop
         if Ptr.H = Fat.Handler_Addr then
            return True;
         end if;

         Ptr := Ptr.Next;
      end loop;

      return False;
   end Is_Registered;

   -----------------
   -- Is_Reserved --
   -----------------

   function Is_Reserved (Interrupt : Interrupt_ID) return Boolean is
   begin
      return IMNG.Reserve (IMNG.Interrupt_ID (Interrupt));
   end Is_Reserved;

   ---------------
   -- Reference --
   ---------------

   function Reference (Interrupt : Interrupt_ID) return System.Address is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return Storage_Elements.To_Address
        (Storage_Elements.Integer_Address (Interrupt));
   end Reference;

   ---------------------------------
   -- Register_Interrupt_Handler  --
   ---------------------------------

   procedure Register_Interrupt_Handler (Handler_Addr : System.Address) is
      New_Node_Ptr : R_Link;

   begin
      --  This routine registers the Handler as usable for Dynamic Interrupt
      --  Handler. Routines attaching and detaching Handler dynamically should
      --  first consult if the Handler is registered. A Program Error should
      --  be raised if it is not registered.

      --  The pragma Interrupt_Handler can only appear in the library level PO
      --  definition and instantiation. Therefore, we do not need to implement
      --  Unregistering operation. Neither we need to protect the queue
      --  structure using a Lock.

      pragma Assert (Handler_Addr /= System.Null_Address);

      New_Node_Ptr := new Registered_Handler;
      New_Node_Ptr.H := Handler_Addr;

      if Registered_Handler_Head = null then
         Registered_Handler_Head := New_Node_Ptr;
         Registered_Handler_Tail := New_Node_Ptr;

      else
         Registered_Handler_Tail.Next := New_Node_Ptr;
         Registered_Handler_Tail := New_Node_Ptr;
      end if;
   end Register_Interrupt_Handler;

   -----------------------
   -- Unblock_Interrupt --
   -----------------------

   procedure Unblock_Interrupt (Interrupt : Interrupt_ID) is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Unblock_Interrupt (Interrupt);
   end Unblock_Interrupt;

   ------------------
   -- Unblocked_By --
   ------------------

   function Unblocked_By
     (Interrupt : Interrupt_ID) return System.Tasking.Task_Id
   is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      return Last_Unblocker (Interrupt);
   end Unblocked_By;

   ------------------------
   -- Unignore_Interrupt --
   ------------------------

   procedure Unignore_Interrupt (Interrupt : Interrupt_ID) is
   begin
      if Is_Reserved (Interrupt) then
         raise Program_Error with
           "Interrupt" & Interrupt_ID'Image (Interrupt) & " is reserved";
      end if;

      Interrupt_Manager.Unignore_Interrupt (Interrupt);
   end Unignore_Interrupt;

   -----------------------
   -- Interrupt_Manager --
   -----------------------

   task body Interrupt_Manager is

      ---------------------
      -- Local Variables --
      ---------------------

      Intwait_Mask  : aliased IMNG.Interrupt_Mask;
      Ret_Interrupt : Interrupt_ID;
      Old_Mask      : aliased IMNG.Interrupt_Mask;
      Old_Handler   : Parameterless_Handler;

      --------------------
      -- Local Routines --
      --------------------

      procedure Bind_Handler (Interrupt : Interrupt_ID);
      --  This procedure does not do anything if the Interrupt is blocked.
      --  Otherwise, we have to interrupt Server_Task for status change through
      --  Wakeup interrupt.

      procedure Unbind_Handler (Interrupt : Interrupt_ID);
      --  This procedure does not do anything if the Interrupt is blocked.
      --  Otherwise, we have to interrupt Server_Task for status change
      --  through abort interrupt.

      procedure Unprotected_Exchange_Handler
        (Old_Handler : out Parameterless_Handler;
         New_Handler : Parameterless_Handler;
         Interrupt   : Interrupt_ID;
         Static      : Boolean;
         Restoration : Boolean := False);

      procedure Unprotected_Detach_Handler
        (Interrupt   : Interrupt_ID;
         Static      : Boolean);

      ------------------
      -- Bind_Handler --
      ------------------

      procedure Bind_Handler (Interrupt : Interrupt_ID) is
      begin
         if not Blocked (Interrupt) then

            --  Mask this task for the given Interrupt so that all tasks
            --  are masked for the Interrupt and the actual delivery of the
            --  Interrupt will be caught using "sigwait" by the
            --  corresponding Server_Task.

            IMOP.Thread_Block_Interrupt (IMNG.Interrupt_ID (Interrupt));

            --  We have installed a Handler or an Entry before we called
            --  this procedure. If the Handler Task is waiting to be awakened,
            --  do it here. Otherwise, the interrupt will be discarded.

            POP.Wakeup (Server_ID (Interrupt), Interrupt_Server_Idle_Sleep);
         end if;
      end Bind_Handler;

      --------------------
      -- Unbind_Handler --
      --------------------

      procedure Unbind_Handler (Interrupt : Interrupt_ID) is
         Server : System.Tasking.Task_Id;
      begin
         if not Blocked (Interrupt) then
            --  Currently, there is a Handler or an Entry attached and
            --  corresponding Server_Task is waiting on "sigwait."
            --  We have to wake up the Server_Task and make it
            --  wait on condition variable by sending an
            --  Abort_Task_Interrupt

            Server := Server_ID (Interrupt);

            case Server.Common.State is
               when Interrupt_Server_Idle_Sleep |
                    Interrupt_Server_Blocked_Interrupt_Sleep
               =>
                  POP.Wakeup (Server, Server.Common.State);

               when Interrupt_Server_Blocked_On_Event_Flag =>
                  POP.Abort_Task (Server);

                  --  Make sure corresponding Server_Task is out of its
                  --  own sigwait state.

                  Ret_Interrupt :=
                    Interrupt_ID (IMOP.Interrupt_Wait (Intwait_Mask'Access));
                  pragma Assert
                    (Ret_Interrupt = Interrupt_ID (IMNG.Abort_Task_Interrupt));

               when Runnable =>
                  null;

               when others =>
                  pragma Assert (False);
                  null;
            end case;

            IMOP.Install_Default_Action (IMNG.Interrupt_ID (Interrupt));

            --  Unmake the Interrupt for this task in order to allow default
            --  action again.

            IMOP.Thread_Unblock_Interrupt (IMNG.Interrupt_ID (Interrupt));

         else
            IMOP.Install_Default_Action (IMNG.Interrupt_ID (Interrupt));
         end if;
      end Unbind_Handler;

      --------------------------------
      -- Unprotected_Detach_Handler --
      --------------------------------

      procedure Unprotected_Detach_Handler
        (Interrupt   : Interrupt_ID;
         Static      : Boolean)
      is
         Old_Handler : Parameterless_Handler;

      begin
         if User_Entry (Interrupt).T /= Null_Task then

            --  In case we have an Interrupt Entry installed.
            --  raise a program error. (propagate it to the caller).

            raise Program_Error with
              "An interrupt entry is already installed";
         end if;

         --  Note : Static = True will pass the following check. That is the
         --  case when we want to detach a handler regardless of the static
         --  status of the current_Handler.

         if not Static and then User_Handler (Interrupt).Static then

            --  Tries to detach a static Interrupt Handler.
            --  raise a program error.

            raise Program_Error with
              "Trying to detach a static Interrupt Handler";
         end if;

         --  The interrupt should no longer be ignored if
         --  it was ever ignored.

         Ignored (Interrupt) := False;

         Old_Handler := User_Handler (Interrupt).H;

         --  The new handler

         User_Handler (Interrupt).H := null;
         User_Handler (Interrupt).Static := False;

         if Old_Handler /= null then
            Unbind_Handler (Interrupt);
         end if;
      end Unprotected_Detach_Handler;

      ----------------------------------
      -- Unprotected_Exchange_Handler --
      ----------------------------------

      procedure Unprotected_Exchange_Handler
        (Old_Handler : out Parameterless_Handler;
         New_Handler : Parameterless_Handler;
         Interrupt   : Interrupt_ID;
         Static      : Boolean;
         Restoration : Boolean := False)
      is
      begin
         if User_Entry (Interrupt).T /= Null_Task then

            --  In case we have an Interrupt Entry already installed.
            --  raise a program error. (propagate it to the caller).

            raise Program_Error with
              "An interrupt is already installed";
         end if;

         --  Note : A null handler with Static = True will pass the
         --  following check. That is the case when we want to Detach a
         --  handler regardless of the Static status of the current_Handler.

         --  We don't check anything if Restoration is True, since we
         --  may be detaching a static handler to restore a dynamic one.

         if not Restoration and then not Static

            --  Tries to overwrite a static Interrupt Handler with a
            --  dynamic Handler

           and then (User_Handler (Interrupt).Static

                        --  The new handler is not specified as an
                        --  Interrupt Handler by a pragma.

                        or else not Is_Registered (New_Handler))
         then
            raise Program_Error with
              "Trying to overwrite a static Interrupt Handler with a " &
              "dynamic Handler";
         end if;

         --  The interrupt should no longer be ignored if
         --  it was ever ignored.

         Ignored (Interrupt) := False;

         --  Save the old handler

         Old_Handler := User_Handler (Interrupt).H;

         --  The new handler

         User_Handler (Interrupt).H := New_Handler;

         if New_Handler = null then

            --  The null handler means we are detaching the handler

            User_Handler (Interrupt).Static := False;

         else
            User_Handler (Interrupt).Static := Static;
         end if;

         --  Invoke a corresponding Server_Task if not yet created.
         --  Place Task_Id info in Server_ID array.

         if Server_ID (Interrupt) = Null_Task then

            --  When a new Server_Task is created, it should have its
            --  signal mask set to the All_Tasks_Mask.

            IMOP.Set_Interrupt_Mask
              (IMOP.All_Tasks_Mask'Access, Old_Mask'Access);
            Access_Hold := new Server_Task (Interrupt);
            IMOP.Set_Interrupt_Mask (Old_Mask'Access);

            Server_ID (Interrupt) := To_System (Access_Hold.all'Identity);
         end if;

         if New_Handler = null then
            if Old_Handler /= null then
               Unbind_Handler (Interrupt);
            end if;

            return;
         end if;

         if Old_Handler = null then
            Bind_Handler (Interrupt);
         end if;
      end Unprotected_Exchange_Handler;

   --  Start of processing for Interrupt_Manager

   begin
      --  By making this task independent of master, when the process
      --  goes away, the Interrupt_Manager will terminate gracefully.

      System.Tasking.Utilities.Make_Independent;

      --  Environment task gets its own interrupt mask, saves it,
      --  and then masks all interrupts except the Keep_Unmasked set.

      --  During rendezvous, the Interrupt_Manager receives the old
      --  interrupt mask of the environment task, and sets its own
      --  interrupt mask to that value.

      --  The environment task will call the entry of Interrupt_Manager some
      --  during elaboration of the body of this package.

      accept Initialize (Mask : IMNG.Interrupt_Mask) do
         declare
            The_Mask : aliased IMNG.Interrupt_Mask;

         begin
            IMOP.Copy_Interrupt_Mask (The_Mask, Mask);
            IMOP.Set_Interrupt_Mask (The_Mask'Access);
         end;
      end Initialize;

      --  Note: All tasks in RTS will have all the Reserve Interrupts
      --  being masked (except the Interrupt_Manager) and Keep_Unmasked
      --  unmasked when created.

      --  Abort_Task_Interrupt is one of the Interrupt unmasked
      --  in all tasks. We mask the Interrupt in this particular task
      --  so that "sigwait" is possible to catch an explicitly sent
      --  Abort_Task_Interrupt from the Server_Tasks.

      --  This sigwaiting is needed so that we make sure a Server_Task is
      --  out of its own sigwait state. This extra synchronization is
      --  necessary to prevent following scenarios.

      --   1) Interrupt_Manager sends an Abort_Task_Interrupt to the
      --      Server_Task then changes its own interrupt mask (OS level).
      --      If an interrupt (corresponding to the Server_Task) arrives
      --      in the mean time we have the Interrupt_Manager unmasked and
      --      the Server_Task waiting on sigwait.

      --   2) For unbinding handler, we install a default action in the
      --      Interrupt_Manager. POSIX.1c states that the result of using
      --      "sigwait" and "sigaction" simultaneously on the same interrupt
      --      is undefined. Therefore, we need to be informed from the
      --      Server_Task of the fact that the Server_Task is out of its
      --      sigwait stage.

      IMOP.Empty_Interrupt_Mask (Intwait_Mask'Access);
      IMOP.Add_To_Interrupt_Mask
        (Intwait_Mask'Access, IMNG.Abort_Task_Interrupt);
      IMOP.Thread_Block_Interrupt
        (IMNG.Abort_Task_Interrupt);

      loop
         --  A block is needed to absorb Program_Error exception

         begin
            select
               accept Attach_Handler
                  (New_Handler : Parameterless_Handler;
                   Interrupt   : Interrupt_ID;
                   Static      : Boolean;
                   Restoration : Boolean := False)
               do
                  Unprotected_Exchange_Handler
                    (Old_Handler, New_Handler, Interrupt, Static, Restoration);
               end Attach_Handler;

            or
               accept Exchange_Handler
                  (Old_Handler : out Parameterless_Handler;
                   New_Handler : Parameterless_Handler;
                   Interrupt   : Interrupt_ID;
                   Static      : Boolean)
               do
                  Unprotected_Exchange_Handler
                    (Old_Handler, New_Handler, Interrupt, Static);
               end Exchange_Handler;

            or
               accept Detach_Handler
                 (Interrupt   : Interrupt_ID;
                  Static      : Boolean)
               do
                  Unprotected_Detach_Handler (Interrupt, Static);
               end Detach_Handler;

            or
               accept Bind_Interrupt_To_Entry
                 (T       : Task_Id;
                  E       : Task_Entry_Index;
                  Interrupt : Interrupt_ID)
               do
                  --  if there is a binding already (either a procedure or an
                  --  entry), raise Program_Error (propagate it to the caller).

                  if User_Handler (Interrupt).H /= null
                    or else User_Entry (Interrupt).T /= Null_Task
                  then
                     raise Program_Error with
                       "A binding for this interrupt is already present";
                  end if;

                  --  The interrupt should no longer be ignored if
                  --  it was ever ignored.

                  Ignored (Interrupt) := False;
                  User_Entry (Interrupt) := Entry_Assoc'(T => T, E => E);

                  --  Indicate the attachment of Interrupt Entry in ATCB.
                  --  This is need so that when an Interrupt Entry task
                  --  terminates the binding can be cleaned. The call to
                  --  unbinding must be made by the task before it terminates.

                  T.Interrupt_Entry := True;

                  --  Invoke a corresponding Server_Task if not yet created.
                  --  Place Task_Id info in Server_ID array.

                  if Server_ID (Interrupt) = Null_Task then

                     --  When a new Server_Task is created, it should have its
                     --  signal mask set to the All_Tasks_Mask.

                     IMOP.Set_Interrupt_Mask
                       (IMOP.All_Tasks_Mask'Access, Old_Mask'Access);
                     Access_Hold := new Server_Task (Interrupt);
                     IMOP.Set_Interrupt_Mask (Old_Mask'Access);
                     Server_ID (Interrupt) :=
                       To_System (Access_Hold.all'Identity);
                  end if;

                  Bind_Handler (Interrupt);
               end Bind_Interrupt_To_Entry;

            or
               accept Detach_Interrupt_Entries (T : Task_Id) do
                  for J in Interrupt_ID'Range loop
                     if not Is_Reserved (J) then
                        if User_Entry (J).T = T then

                           --  The interrupt should no longer be ignored if
                           --  it was ever ignored.

                           Ignored (J) := False;
                           User_Entry (J) := Entry_Assoc'
                             (T => Null_Task, E => Null_Task_Entry);
                           Unbind_Handler (J);
                        end if;
                     end if;
                  end loop;

                  --  Indicate in ATCB that no Interrupt Entries are attached

                  T.Interrupt_Entry := False;
               end Detach_Interrupt_Entries;

            or
               accept Block_Interrupt (Interrupt : Interrupt_ID) do
                  if Blocked (Interrupt) then
                     return;
                  end if;

                  Blocked (Interrupt) := True;
                  Last_Unblocker (Interrupt) := Null_Task;

                  --  Mask this task for the given Interrupt so that all tasks
                  --  are masked for the Interrupt.

                  IMOP.Thread_Block_Interrupt (IMNG.Interrupt_ID (Interrupt));

                  if User_Handler (Interrupt).H /= null
                    or else User_Entry (Interrupt).T /= Null_Task
                  then
                     --  This is the case where the Server_Task is waiting
                     --  on "sigwait." Wake it up by sending an
                     --  Abort_Task_Interrupt so that the Server_Task
                     --  waits on Cond.

                     POP.Abort_Task (Server_ID (Interrupt));

                     --  Make sure corresponding Server_Task is out of its own
                     --  sigwait state.

                     Ret_Interrupt := Interrupt_ID
                       (IMOP.Interrupt_Wait (Intwait_Mask'Access));
                     pragma Assert
                       (Ret_Interrupt =
                        Interrupt_ID (IMNG.Abort_Task_Interrupt));
                  end if;
               end Block_Interrupt;

            or
               accept Unblock_Interrupt (Interrupt : Interrupt_ID) do
                  if not Blocked (Interrupt) then
                     return;
                  end if;

                  Blocked (Interrupt) := False;
                  Last_Unblocker (Interrupt) :=
                    To_System (Unblock_Interrupt'Caller);

                  if User_Handler (Interrupt).H = null
                    and then User_Entry (Interrupt).T = Null_Task
                  then
                     --  No handler is attached. Unmask the Interrupt so that
                     --  the default action can be carried out.

                     IMOP.Thread_Unblock_Interrupt
                       (IMNG.Interrupt_ID (Interrupt));

                  else
                     --  The Server_Task must be waiting on the Cond variable
                     --  since it was being blocked and an Interrupt Hander or
                     --  an Entry was there. Wake it up and let it change
                     --  it place of waiting according to its new state.

                     POP.Wakeup (Server_ID (Interrupt),
                       Interrupt_Server_Blocked_Interrupt_Sleep);
                  end if;
               end Unblock_Interrupt;

            or
               accept Ignore_Interrupt (Interrupt : Interrupt_ID) do
                  if Ignored (Interrupt) then
                     return;
                  end if;

                  Ignored (Interrupt) := True;

                  --  If there is a handler associated with the Interrupt,
                  --  detach it first. In this way we make sure that the
                  --  Server_Task is not on sigwait. This is legal since
                  --  Unignore_Interrupt is to install the default action.

                  if User_Handler (Interrupt).H /= null then
                     Unprotected_Detach_Handler
                       (Interrupt => Interrupt, Static => True);

                  elsif User_Entry (Interrupt).T /= Null_Task then
                     User_Entry (Interrupt) := Entry_Assoc'
                       (T => Null_Task, E => Null_Task_Entry);
                     Unbind_Handler (Interrupt);
                  end if;

                  IMOP.Install_Ignore_Action (IMNG.Interrupt_ID (Interrupt));
               end Ignore_Interrupt;

            or
               accept Unignore_Interrupt (Interrupt : Interrupt_ID) do
                  Ignored (Interrupt) := False;

                  --  If there is a handler associated with the Interrupt,
                  --  detach it first. In this way we make sure that the
                  --  Server_Task is not on sigwait. This is legal since
                  --  Unignore_Interrupt is to install the default action.

                  if User_Handler (Interrupt).H /= null then
                     Unprotected_Detach_Handler
                       (Interrupt => Interrupt, Static => True);

                  elsif User_Entry (Interrupt).T /= Null_Task then
                     User_Entry (Interrupt) := Entry_Assoc'
                       (T => Null_Task, E => Null_Task_Entry);
                     Unbind_Handler (Interrupt);
                  end if;

                  IMOP.Install_Default_Action (IMNG.Interrupt_ID (Interrupt));
               end Unignore_Interrupt;
            end select;

         exception
            --  If there is a program error we just want to propagate it to
            --  the caller and do not want to stop this task.

            when Program_Error =>
               null;

            when others =>
               pragma Assert (False);
               null;
         end;
      end loop;
   end Interrupt_Manager;

   -----------------
   -- Server_Task --
   -----------------

   task body Server_Task is
      Intwait_Mask    : aliased IMNG.Interrupt_Mask;
      Ret_Interrupt   : Interrupt_ID;
      Self_ID         : constant Task_Id := Self;
      Tmp_Handler     : Parameterless_Handler;
      Tmp_ID          : Task_Id;
      Tmp_Entry_Index : Task_Entry_Index;

   begin
      --  By making this task independent of master, when the process
      --  goes away, the Server_Task will terminate gracefully.

      System.Tasking.Utilities.Make_Independent;

      --  Install default action in system level

      IMOP.Install_Default_Action (IMNG.Interrupt_ID (Interrupt));

      --  Note: All tasks in RTS will have all the Reserve Interrupts being
      --  masked (except the Interrupt_Manager) and Keep_Unmasked unmasked when
      --  created.

      --  Abort_Task_Interrupt is one of the Interrupt unmasked in all tasks.
      --  We mask the Interrupt in this particular task so that "sigwait" is
      --  possible to catch an explicitly sent Abort_Task_Interrupt from the
      --  Interrupt_Manager.

      --  There are two Interrupt interrupts that this task catch through
      --  "sigwait." One is the Interrupt this task is designated to catch
      --  in order to execute user handler or entry. The other one is the
      --  Abort_Task_Interrupt. This interrupt is being sent from the
      --  Interrupt_Manager to inform status changes (e.g: become Blocked,
      --  Handler or Entry is to be detached).

      --  Prepare a mask to used for sigwait

      IMOP.Empty_Interrupt_Mask (Intwait_Mask'Access);

      IMOP.Add_To_Interrupt_Mask
        (Intwait_Mask'Access, IMNG.Interrupt_ID (Interrupt));

      IMOP.Add_To_Interrupt_Mask
        (Intwait_Mask'Access, IMNG.Abort_Task_Interrupt);

      IMOP.Thread_Block_Interrupt
        (IMNG.Abort_Task_Interrupt);

      PIO.Set_Interrupt_ID (IMNG.Interrupt_ID (Interrupt), Self_ID);

      loop
         System.Tasking.Initialization.Defer_Abort (Self_ID);

         if Single_Lock then
            POP.Lock_RTS;
         end if;

         POP.Write_Lock (Self_ID);

         if User_Handler (Interrupt).H = null
           and then User_Entry (Interrupt).T = Null_Task
         then
            --  No Interrupt binding. If there is an interrupt,
            --  Interrupt_Manager will take default action.

            Self_ID.Common.State := Interrupt_Server_Blocked_Interrupt_Sleep;
            POP.Sleep (Self_ID, Interrupt_Server_Idle_Sleep);
            Self_ID.Common.State := Runnable;

         elsif Blocked (Interrupt) then

            --  Interrupt is blocked. Stay here, so we won't catch
            --  the Interrupt.

            Self_ID.Common.State := Interrupt_Server_Blocked_Interrupt_Sleep;
            POP.Sleep (Self_ID, Interrupt_Server_Blocked_Interrupt_Sleep);
            Self_ID.Common.State := Runnable;

         else
            --  A Handler or an Entry is installed. At this point all tasks
            --  mask for the Interrupt is masked. Catch the Interrupt using
            --  sigwait.

            --  This task may wake up from sigwait by receiving an interrupt
            --  (Abort_Task_Interrupt) from the Interrupt_Manager for unbinding
            --  a Procedure Handler or an Entry. Or it could be a wake up
            --  from status change (Unblocked -> Blocked). If that is not
            --  the case, we should execute the attached Procedure or Entry.

            Self_ID.Common.State := Interrupt_Server_Blocked_On_Event_Flag;
            POP.Unlock (Self_ID);

            if Single_Lock then
               POP.Unlock_RTS;
            end if;

            --  Avoid race condition when terminating application and
            --  System.Parameters.No_Abort is True.

            if Parameters.No_Abort and then Self_ID.Pending_Action then
               Initialization.Do_Pending_Action (Self_ID);
            end if;

            Ret_Interrupt :=
              Interrupt_ID (IMOP.Interrupt_Wait (Intwait_Mask'Access));
            Self_ID.Common.State := Runnable;

            if Ret_Interrupt = Interrupt_ID (IMNG.Abort_Task_Interrupt) then

               --  Inform the Interrupt_Manager of wakeup from above sigwait

               POP.Abort_Task (Interrupt_Manager_ID);

               if Single_Lock then
                  POP.Lock_RTS;
               end if;

               POP.Write_Lock (Self_ID);

            else
               if Single_Lock then
                  POP.Lock_RTS;
               end if;

               POP.Write_Lock (Self_ID);

               if Ret_Interrupt /= Interrupt then

                  --  On some systems (e.g. recent linux kernels), sigwait
                  --  may return unexpectedly (with errno set to EINTR).

                  null;

               else
                  --  Even though we have received an Interrupt the status may
                  --  have changed already before we got the Self_ID lock above
                  --  Therefore we make sure a Handler or an Entry is still
                  --  there and make appropriate call.

                  --  If there is no calls to make we need to regenerate the
                  --  Interrupt in order not to lose it.

                  if User_Handler (Interrupt).H /= null then
                     Tmp_Handler := User_Handler (Interrupt).H;

                     --  RTS calls should not be made with self being locked

                     POP.Unlock (Self_ID);

                     if Single_Lock then
                        POP.Unlock_RTS;
                     end if;

                     Tmp_Handler.all;

                     if Single_Lock then
                        POP.Lock_RTS;
                     end if;

                     POP.Write_Lock (Self_ID);

                  elsif User_Entry (Interrupt).T /= Null_Task then
                     Tmp_ID := User_Entry (Interrupt).T;
                     Tmp_Entry_Index := User_Entry (Interrupt).E;

                     --  RTS calls should not be made with self being locked

                     if Single_Lock then
                        POP.Unlock_RTS;
                     end if;

                     POP.Unlock (Self_ID);

                     System.Tasking.Rendezvous.Call_Simple
                       (Tmp_ID, Tmp_Entry_Index, System.Null_Address);

                     POP.Write_Lock (Self_ID);

                     if Single_Lock then
                        POP.Lock_RTS;
                     end if;

                  else
                     --  This is a situation that this task wakes up receiving
                     --  an Interrupt and before it gets the lock the Interrupt
                     --  is blocked. We do not want to lose the interrupt in
                     --  this case so we regenerate the Interrupt to process
                     --  level.

                     IMOP.Interrupt_Self_Process
                       (IMNG.Interrupt_ID (Interrupt));
                  end if;
               end if;
            end if;
         end if;

         POP.Unlock (Self_ID);

         if Single_Lock then
            POP.Unlock_RTS;
         end if;

         System.Tasking.Initialization.Undefer_Abort (Self_ID);

         if Self_ID.Pending_Action then
            Initialization.Do_Pending_Action (Self_ID);
         end if;

         --  Undefer abort here to allow a window for this task to be aborted
         --  at the time of system shutdown. We also explicitly test for
         --  Pending_Action in case System.Parameters.No_Abort is True.

      end loop;
   end Server_Task;

--  Elaboration code for package System.Interrupts

begin
   --  Get Interrupt_Manager's ID so that Abort_Interrupt can be sent

   Interrupt_Manager_ID := To_System (Interrupt_Manager'Identity);

   --  During the elaboration of this package body we want the RTS
   --  to inherit the interrupt mask from the Environment Task.

   IMOP.Setup_Interrupt_Mask;

   --  The environment task should have gotten its mask from the enclosing
   --  process during the RTS start up. (See processing in s-inmaop.adb). Pass
   --  the Interrupt_Mask of the environment task to the Interrupt_Manager.

   --  Note: At this point we know that all tasks are masked for non-reserved
   --  signals. Only the Interrupt_Manager will have masks set up differently
   --  inheriting the original environment task's mask.

   Interrupt_Manager.Initialize (IMOP.Environment_Mask);
end System.Interrupts;
