path: root/gcc/ada/s-taprop-hpux-dce.adb

------------------------------------------------------------------------------
--                                                                          --
--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
--                                                                          --
--     S Y S T E M . T A S K _ P R I M I T I V E S . O P E R A T I O N S    --
--                                                                          --
--                                  B o d y                                 --
--                                                                          --
--         Copyright (C) 1992-2009, 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.     --
--                                                                          --
------------------------------------------------------------------------------

--  This is a HP-UX DCE threads (HPUX 10) version of this package

--  This package contains all the GNULL primitives that interface directly with
--  the underlying OS.

pragma Polling (Off);
--  Turn off polling, we do not want ATC polling to take place during tasking
--  operations. It causes infinite loops and other problems.

with Ada.Unchecked_Conversion;
with Ada.Unchecked_Deallocation;

with Interfaces.C;

with System.Tasking.Debug;
with System.Interrupt_Management;
with System.OS_Primitives;
with System.Task_Primitives.Interrupt_Operations;

pragma Warnings (Off);
with System.Interrupt_Management.Operations;
pragma Elaborate_All (System.Interrupt_Management.Operations);
pragma Warnings (On);

with System.Soft_Links;
--  We use System.Soft_Links instead of System.Tasking.Initialization
--  because the later is a higher level package that we shouldn't depend on.
--  For example when using the restricted run time, it is replaced by
--  System.Tasking.Restricted.Stages.

package body System.Task_Primitives.Operations is

   package SSL renames System.Soft_Links;

   use System.Tasking.Debug;
   use System.Tasking;
   use Interfaces.C;
   use System.OS_Interface;
   use System.Parameters;
   use System.OS_Primitives;

   package PIO renames System.Task_Primitives.Interrupt_Operations;

   ----------------
   -- Local Data --
   ----------------

   --  The followings are logically constants, but need to be initialized
   --  at run time.

   Single_RTS_Lock : aliased RTS_Lock;
   --  This is a lock to allow only one thread of control in the RTS at
   --  a time; it is used to execute in mutual exclusion from all other tasks.
   --  Used mainly in Single_Lock mode, but also to protect All_Tasks_List

   ATCB_Key : aliased pthread_key_t;
   --  Key used to find the Ada Task_Id associated with a thread

   Environment_Task_Id : Task_Id;
   --  A variable to hold Task_Id for the environment task

   Unblocked_Signal_Mask : aliased sigset_t;
   --  The set of signals that should unblocked in all tasks

   Time_Slice_Val : Integer;
   pragma Import (C, Time_Slice_Val, "__gl_time_slice_val");

   Dispatching_Policy : Character;
   pragma Import (C, Dispatching_Policy, "__gl_task_dispatching_policy");

   --  Note: the reason that Locking_Policy is not needed is that this
   --  is not implemented for DCE threads. The HPUX 10 port is at this
   --  stage considered dead, and no further work is planned on it.

   Foreign_Task_Elaborated : aliased Boolean := True;
   --  Used to identified fake tasks (i.e., non-Ada Threads)

   --------------------
   -- Local Packages --
   --------------------

   package Specific is

      procedure Initialize (Environment_Task : Task_Id);
      pragma Inline (Initialize);
      --  Initialize various data needed by this package

      function Is_Valid_Task return Boolean;
      pragma Inline (Is_Valid_Task);
      --  Does the executing thread have a TCB?

      procedure Set (Self_Id : Task_Id);
      pragma Inline (Set);
      --  Set the self id for the current task

      function Self return Task_Id;
      pragma Inline (Self);
      --  Return a pointer to the Ada Task Control Block of the calling task

   end Specific;

   package body Specific is separate;
   --  The body of this package is target specific

   ---------------------------------
   -- Support for foreign threads --
   ---------------------------------

   function Register_Foreign_Thread (Thread : Thread_Id) return Task_Id;
   --  Allocate and Initialize a new ATCB for the current Thread

   function Register_Foreign_Thread
     (Thread : Thread_Id) return Task_Id is separate;

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

   procedure Abort_Handler (Sig : Signal);

   function To_Address is
     new Ada.Unchecked_Conversion (Task_Id, System.Address);

   -------------------
   -- Abort_Handler --
   -------------------

   procedure Abort_Handler (Sig : Signal) is
      pragma Unreferenced (Sig);

      Self_Id : constant Task_Id := Self;
      Result  : Interfaces.C.int;
      Old_Set : aliased sigset_t;

   begin
      if Self_Id.Deferral_Level = 0
        and then Self_Id.Pending_ATC_Level < Self_Id.ATC_Nesting_Level
        and then not Self_Id.Aborting
      then
         Self_Id.Aborting := True;

         --  Make sure signals used for RTS internal purpose are unmasked

         Result :=
           pthread_sigmask
             (SIG_UNBLOCK,
              Unblocked_Signal_Mask'Access,
              Old_Set'Access);
         pragma Assert (Result = 0);

         raise Standard'Abort_Signal;
      end if;
   end Abort_Handler;

   -----------------
   -- Stack_Guard --
   -----------------

   --  The underlying thread system sets a guard page at the bottom of a thread
   --  stack, so nothing is needed.
   --  ??? Check the comment above

   procedure Stack_Guard (T : ST.Task_Id; On : Boolean) is
      pragma Unreferenced (T, On);
   begin
      null;
   end Stack_Guard;

   -------------------
   -- Get_Thread_Id --
   -------------------

   function Get_Thread_Id (T : ST.Task_Id) return OSI.Thread_Id is
   begin
      return T.Common.LL.Thread;
   end Get_Thread_Id;

   ----------
   -- Self --
   ----------

   function Self return Task_Id renames Specific.Self;

   ---------------------
   -- Initialize_Lock --
   ---------------------

   --  Note: mutexes and cond_variables needed per-task basis are initialized
   --  in Initialize_TCB and the Storage_Error is handled. Other mutexes (such
   --  as RTS_Lock, Memory_Lock...) used in RTS is initialized before any
   --  status change of RTS. Therefore raising Storage_Error in the following
   --  routines should be able to be handled safely.

   procedure Initialize_Lock
     (Prio : System.Any_Priority;
      L    : not null access Lock)
   is
      Attributes : aliased pthread_mutexattr_t;
      Result     : Interfaces.C.int;

   begin
      Result := pthread_mutexattr_init (Attributes'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = ENOMEM then
         raise Storage_Error;
      end if;

      L.Priority := Prio;

      Result := pthread_mutex_init (L.L'Access, Attributes'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = ENOMEM then
         raise Storage_Error;
      end if;

      Result := pthread_mutexattr_destroy (Attributes'Access);
      pragma Assert (Result = 0);
   end Initialize_Lock;

   procedure Initialize_Lock
     (L     : not null access RTS_Lock;
      Level : Lock_Level)
   is
      pragma Unreferenced (Level);

      Attributes : aliased pthread_mutexattr_t;
      Result     : Interfaces.C.int;

   begin
      Result := pthread_mutexattr_init (Attributes'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = ENOMEM then
         raise Storage_Error;
      end if;

      Result := pthread_mutex_init (L, Attributes'Access);

      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = ENOMEM then
         raise Storage_Error;
      end if;

      Result := pthread_mutexattr_destroy (Attributes'Access);
      pragma Assert (Result = 0);
   end Initialize_Lock;

   -------------------
   -- Finalize_Lock --
   -------------------

   procedure Finalize_Lock (L : not null access Lock) is
      Result : Interfaces.C.int;
   begin
      Result := pthread_mutex_destroy (L.L'Access);
      pragma Assert (Result = 0);
   end Finalize_Lock;

   procedure Finalize_Lock (L : not null access RTS_Lock) is
      Result : Interfaces.C.int;
   begin
      Result := pthread_mutex_destroy (L);
      pragma Assert (Result = 0);
   end Finalize_Lock;

   ----------------
   -- Write_Lock --
   ----------------

   procedure Write_Lock
     (L                 : not null access Lock;
      Ceiling_Violation : out Boolean)
   is
      Result : Interfaces.C.int;

   begin
      L.Owner_Priority := Get_Priority (Self);

      if L.Priority < L.Owner_Priority then
         Ceiling_Violation := True;
         return;
      end if;

      Result := pthread_mutex_lock (L.L'Access);
      pragma Assert (Result = 0);
      Ceiling_Violation := False;
   end Write_Lock;

   procedure Write_Lock
     (L           : not null access RTS_Lock;
      Global_Lock : Boolean := False)
   is
      Result : Interfaces.C.int;
   begin
      if not Single_Lock or else Global_Lock then
         Result := pthread_mutex_lock (L);
         pragma Assert (Result = 0);
      end if;
   end Write_Lock;

   procedure Write_Lock (T : Task_Id) is
      Result : Interfaces.C.int;
   begin
      if not Single_Lock then
         Result := pthread_mutex_lock (T.Common.LL.L'Access);
         pragma Assert (Result = 0);
      end if;
   end Write_Lock;

   ---------------
   -- Read_Lock --
   ---------------

   procedure Read_Lock
     (L                 : not null access Lock;
      Ceiling_Violation : out Boolean)
   is
   begin
      Write_Lock (L, Ceiling_Violation);
   end Read_Lock;

   ------------
   -- Unlock --
   ------------

   procedure Unlock (L : not null access Lock) is
      Result : Interfaces.C.int;
   begin
      Result := pthread_mutex_unlock (L.L'Access);
      pragma Assert (Result = 0);
   end Unlock;

   procedure Unlock
     (L           : not null access RTS_Lock;
      Global_Lock : Boolean := False)
   is
      Result : Interfaces.C.int;
   begin
      if not Single_Lock or else Global_Lock then
         Result := pthread_mutex_unlock (L);
         pragma Assert (Result = 0);
      end if;
   end Unlock;

   procedure Unlock (T : Task_Id) is
      Result : Interfaces.C.int;
   begin
      if not Single_Lock then
         Result := pthread_mutex_unlock (T.Common.LL.L'Access);
         pragma Assert (Result = 0);
      end if;
   end Unlock;

   -----------------
   -- Set_Ceiling --
   -----------------

   --  Dynamic priority ceilings are not supported by the underlying system

   procedure Set_Ceiling
     (L    : not null access Lock;
      Prio : System.Any_Priority)
   is
      pragma Unreferenced (L, Prio);
   begin
      null;
   end Set_Ceiling;

   -----------
   -- Sleep --
   -----------

   procedure Sleep
     (Self_ID : Task_Id;
      Reason  : System.Tasking.Task_States)
   is
      pragma Unreferenced (Reason);

      Result : Interfaces.C.int;

   begin
      Result :=
        pthread_cond_wait
          (cond  => Self_ID.Common.LL.CV'Access,
           mutex => (if Single_Lock
                     then Single_RTS_Lock'Access
                     else Self_ID.Common.LL.L'Access));

      --  EINTR is not considered a failure

      pragma Assert (Result = 0 or else Result = EINTR);
   end Sleep;

   -----------------
   -- Timed_Sleep --
   -----------------

   procedure Timed_Sleep
     (Self_ID  : Task_Id;
      Time     : Duration;
      Mode     : ST.Delay_Modes;
      Reason   : System.Tasking.Task_States;
      Timedout : out Boolean;
      Yielded  : out Boolean)
   is
      pragma Unreferenced (Reason);

      Check_Time : constant Duration := Monotonic_Clock;
      Abs_Time   : Duration;
      Request    : aliased timespec;
      Result     : Interfaces.C.int;

   begin
      Timedout := True;
      Yielded := False;

      Abs_Time :=
        (if Mode = Relative
         then Duration'Min (Time, Max_Sensible_Delay) + Check_Time
         else Duration'Min (Check_Time + Max_Sensible_Delay, Time));

      if Abs_Time > Check_Time then
         Request := To_Timespec (Abs_Time);

         loop
            exit when Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level;

            Result :=
              pthread_cond_timedwait
                (cond    => Self_ID.Common.LL.CV'Access,
                 mutex   => (if Single_Lock
                             then Single_RTS_Lock'Access
                             else Self_ID.Common.LL.L'Access),
                 abstime => Request'Access);

            exit when Abs_Time <= Monotonic_Clock;

            if Result = 0 or Result = EINTR then

               --  Somebody may have called Wakeup for us

               Timedout := False;
               exit;
            end if;

            pragma Assert (Result = ETIMEDOUT);
         end loop;
      end if;
   end Timed_Sleep;

   -----------------
   -- Timed_Delay --
   -----------------

   procedure Timed_Delay
     (Self_ID : Task_Id;
      Time    : Duration;
      Mode    : ST.Delay_Modes)
   is
      Check_Time : constant Duration := Monotonic_Clock;
      Abs_Time   : Duration;
      Request    : aliased timespec;

      Result : Interfaces.C.int;
      pragma Warnings (Off, Result);

   begin
      if Single_Lock then
         Lock_RTS;
      end if;

      Write_Lock (Self_ID);

      Abs_Time :=
        (if Mode = Relative
         then Time + Check_Time
         else Duration'Min (Check_Time + Max_Sensible_Delay, Time));

      if Abs_Time > Check_Time then
         Request := To_Timespec (Abs_Time);
         Self_ID.Common.State := Delay_Sleep;

         loop
            exit when Self_ID.Pending_ATC_Level < Self_ID.ATC_Nesting_Level;

            Result :=
              pthread_cond_timedwait
                (cond    => Self_ID.Common.LL.CV'Access,
                 mutex   => (if Single_Lock
                             then Single_RTS_Lock'Access
                             else Self_ID.Common.LL.L'Access),
                 abstime => Request'Access);

            exit when Abs_Time <= Monotonic_Clock;

            pragma Assert (Result = 0 or else
              Result = ETIMEDOUT or else
              Result = EINTR);
         end loop;

         Self_ID.Common.State := Runnable;
      end if;

      Unlock (Self_ID);

      if Single_Lock then
         Unlock_RTS;
      end if;

      Result := sched_yield;
   end Timed_Delay;

   ---------------------
   -- Monotonic_Clock --
   ---------------------

   function Monotonic_Clock return Duration is
      TS     : aliased timespec;
      Result : Interfaces.C.int;
   begin
      Result := Clock_Gettime (CLOCK_REALTIME, TS'Unchecked_Access);
      pragma Assert (Result = 0);
      return To_Duration (TS);
   end Monotonic_Clock;

   -------------------
   -- RT_Resolution --
   -------------------

   function RT_Resolution return Duration is
   begin
      return 10#1.0#E-6;
   end RT_Resolution;

   ------------
   -- Wakeup --
   ------------

   procedure Wakeup (T : Task_Id; Reason : System.Tasking.Task_States) is
      pragma Unreferenced (Reason);
      Result : Interfaces.C.int;
   begin
      Result := pthread_cond_signal (T.Common.LL.CV'Access);
      pragma Assert (Result = 0);
   end Wakeup;

   -----------
   -- Yield --
   -----------

   procedure Yield (Do_Yield : Boolean := True) is
      Result : Interfaces.C.int;
      pragma Unreferenced (Result);
   begin
      if Do_Yield then
         Result := sched_yield;
      end if;
   end Yield;

   ------------------
   -- Set_Priority --
   ------------------

   type Prio_Array_Type is array (System.Any_Priority) of Integer;
   pragma Atomic_Components (Prio_Array_Type);

   Prio_Array : Prio_Array_Type;
   --  Global array containing the id of the currently running task for
   --  each priority.
   --
   --  Note: assume we are on single processor with run-til-blocked scheduling

   procedure Set_Priority
     (T                   : Task_Id;
      Prio                : System.Any_Priority;
      Loss_Of_Inheritance : Boolean := False)
   is
      Result     : Interfaces.C.int;
      Array_Item : Integer;
      Param      : aliased struct_sched_param;

      function Get_Policy (Prio : System.Any_Priority) return Character;
      pragma Import (C, Get_Policy, "__gnat_get_specific_dispatching");
      --  Get priority specific dispatching policy

      Priority_Specific_Policy : constant Character := Get_Policy (Prio);
      --  Upper case first character of the policy name corresponding to the
      --  task as set by a Priority_Specific_Dispatching pragma.

   begin
      Param.sched_priority  := Interfaces.C.int (Underlying_Priorities (Prio));

      if Dispatching_Policy = 'R'
        or else Priority_Specific_Policy = 'R'
        or else Time_Slice_Val > 0
      then
         Result :=
           pthread_setschedparam
             (T.Common.LL.Thread, SCHED_RR, Param'Access);

      elsif Dispatching_Policy = 'F'
        or else Priority_Specific_Policy = 'F'
        or else Time_Slice_Val = 0
      then
         Result :=
           pthread_setschedparam
             (T.Common.LL.Thread, SCHED_FIFO, Param'Access);

      else
         Result :=
           pthread_setschedparam
             (T.Common.LL.Thread, SCHED_OTHER, Param'Access);
      end if;

      pragma Assert (Result = 0);

      if Dispatching_Policy = 'F' or else Priority_Specific_Policy = 'F' then

         --  Annex D requirement [RM D.2.2 par. 9]:
         --    If the task drops its priority due to the loss of inherited
         --    priority, it is added at the head of the ready queue for its
         --    new active priority.

         if Loss_Of_Inheritance
           and then Prio < T.Common.Current_Priority
         then
            Array_Item := Prio_Array (T.Common.Base_Priority) + 1;
            Prio_Array (T.Common.Base_Priority) := Array_Item;

            loop
               --  Let some processes a chance to arrive

               Yield;

               --  Then wait for our turn to proceed

               exit when Array_Item = Prio_Array (T.Common.Base_Priority)
                 or else Prio_Array (T.Common.Base_Priority) = 1;
            end loop;

            Prio_Array (T.Common.Base_Priority) :=
              Prio_Array (T.Common.Base_Priority) - 1;
         end if;
      end if;

      T.Common.Current_Priority := Prio;
   end Set_Priority;

   ------------------
   -- Get_Priority --
   ------------------

   function Get_Priority (T : Task_Id) return System.Any_Priority is
   begin
      return T.Common.Current_Priority;
   end Get_Priority;

   ----------------
   -- Enter_Task --
   ----------------

   procedure Enter_Task (Self_ID : Task_Id) is
   begin
      Self_ID.Common.LL.Thread := pthread_self;
      Specific.Set (Self_ID);
   end Enter_Task;

   --------------
   -- New_ATCB --
   --------------

   function New_ATCB (Entry_Num : Task_Entry_Index) return Task_Id is
   begin
      return new Ada_Task_Control_Block (Entry_Num);
   end New_ATCB;

   -------------------
   -- Is_Valid_Task --
   -------------------

   function Is_Valid_Task return Boolean renames Specific.Is_Valid_Task;

   -----------------------------
   -- Register_Foreign_Thread --
   -----------------------------

   function Register_Foreign_Thread return Task_Id is
   begin
      if Is_Valid_Task then
         return Self;
      else
         return Register_Foreign_Thread (pthread_self);
      end if;
   end Register_Foreign_Thread;

   --------------------
   -- Initialize_TCB --
   --------------------

   procedure Initialize_TCB (Self_ID : Task_Id; Succeeded : out Boolean) is
      Mutex_Attr : aliased pthread_mutexattr_t;
      Result     : Interfaces.C.int;
      Cond_Attr  : aliased pthread_condattr_t;

   begin
      if not Single_Lock then
         Result := pthread_mutexattr_init (Mutex_Attr'Access);
         pragma Assert (Result = 0 or else Result = ENOMEM);

         if Result = 0 then
            Result :=
              pthread_mutex_init
                (Self_ID.Common.LL.L'Access, Mutex_Attr'Access);
            pragma Assert (Result = 0 or else Result = ENOMEM);
         end if;

         if Result /= 0 then
            Succeeded := False;
            return;
         end if;

         Result := pthread_mutexattr_destroy (Mutex_Attr'Access);
         pragma Assert (Result = 0);
      end if;

      Result := pthread_condattr_init (Cond_Attr'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = 0 then
         Result :=
           pthread_cond_init
             (Self_ID.Common.LL.CV'Access,
              Cond_Attr'Access);
         pragma Assert (Result = 0 or else Result = ENOMEM);
      end if;

      if Result = 0 then
         Succeeded := True;
      else
         if not Single_Lock then
            Result := pthread_mutex_destroy (Self_ID.Common.LL.L'Access);
            pragma Assert (Result = 0);
         end if;

         Succeeded := False;
      end if;

      Result := pthread_condattr_destroy (Cond_Attr'Access);
      pragma Assert (Result = 0);
   end Initialize_TCB;

   -----------------
   -- Create_Task --
   -----------------

   procedure Create_Task
     (T          : Task_Id;
      Wrapper    : System.Address;
      Stack_Size : System.Parameters.Size_Type;
      Priority   : System.Any_Priority;
      Succeeded  : out Boolean)
   is
      Attributes : aliased pthread_attr_t;
      Result     : Interfaces.C.int;

      function Thread_Body_Access is new
        Ada.Unchecked_Conversion (System.Address, Thread_Body);

   begin
      Result := pthread_attr_init (Attributes'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result /= 0 then
         Succeeded := False;
         return;
      end if;

      Result := pthread_attr_setstacksize
        (Attributes'Access, Interfaces.C.size_t (Stack_Size));
      pragma Assert (Result = 0);

      --  Since the initial signal mask of a thread is inherited from the
      --  creator, and the Environment task has all its signals masked, we
      --  do not need to manipulate caller's signal mask at this point.
      --  All tasks in RTS will have All_Tasks_Mask initially.

      Result := pthread_create
        (T.Common.LL.Thread'Access,
         Attributes'Access,
         Thread_Body_Access (Wrapper),
         To_Address (T));
      pragma Assert (Result = 0 or else Result = EAGAIN);

      Succeeded := Result = 0;

      pthread_detach (T.Common.LL.Thread'Access);
      --  Detach the thread using pthread_detach, since DCE threads do not have
      --  pthread_attr_set_detachstate.

      Result := pthread_attr_destroy (Attributes'Access);
      pragma Assert (Result = 0);

      Set_Priority (T, Priority);
   end Create_Task;

   ------------------
   -- Finalize_TCB --
   ------------------

   procedure Finalize_TCB (T : Task_Id) is
      Result  : Interfaces.C.int;
      Tmp     : Task_Id := T;
      Is_Self : constant Boolean := T = Self;

      procedure Free is new
        Ada.Unchecked_Deallocation (Ada_Task_Control_Block, Task_Id);

   begin
      if not Single_Lock then
         Result := pthread_mutex_destroy (T.Common.LL.L'Access);
         pragma Assert (Result = 0);
      end if;

      Result := pthread_cond_destroy (T.Common.LL.CV'Access);
      pragma Assert (Result = 0);

      if T.Known_Tasks_Index /= -1 then
         Known_Tasks (T.Known_Tasks_Index) := null;
      end if;

      Free (Tmp);

      if Is_Self then
         Specific.Set (null);
      end if;
   end Finalize_TCB;

   ---------------
   -- Exit_Task --
   ---------------

   procedure Exit_Task is
   begin
      Specific.Set (null);
   end Exit_Task;

   ----------------
   -- Abort_Task --
   ----------------

   procedure Abort_Task (T : Task_Id) is
   begin
      --  Interrupt Server_Tasks may be waiting on an "event" flag (signal)

      if T.Common.State = Interrupt_Server_Blocked_On_Event_Flag then
         System.Interrupt_Management.Operations.Interrupt_Self_Process
           (PIO.Get_Interrupt_ID (T));
      end if;
   end Abort_Task;

   ----------------
   -- Initialize --
   ----------------

   procedure Initialize (S : in out Suspension_Object) is
      Mutex_Attr : aliased pthread_mutexattr_t;
      Cond_Attr  : aliased pthread_condattr_t;
      Result     : Interfaces.C.int;
   begin
      --  Initialize internal state (always to False (ARM D.10(6)))

      S.State := False;
      S.Waiting := False;

      --  Initialize internal mutex

      Result := pthread_mutex_init (S.L'Access, Mutex_Attr'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result = ENOMEM then
         raise Storage_Error;
      end if;

      --  Initialize internal condition variable

      Result := pthread_cond_init (S.CV'Access, Cond_Attr'Access);
      pragma Assert (Result = 0 or else Result = ENOMEM);

      if Result /= 0 then
         Result := pthread_mutex_destroy (S.L'Access);
         pragma Assert (Result = 0);

         if Result = ENOMEM then
            raise Storage_Error;
         end if;
      end if;
   end Initialize;

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

   procedure Finalize (S : in out Suspension_Object) is
      Result  : Interfaces.C.int;

   begin
      --  Destroy internal mutex

      Result := pthread_mutex_destroy (S.L'Access);
      pragma Assert (Result = 0);

      --  Destroy internal condition variable

      Result := pthread_cond_destroy (S.CV'Access);
      pragma Assert (Result = 0);
   end Finalize;

   -------------------
   -- Current_State --
   -------------------

   function Current_State (S : Suspension_Object) return Boolean is
   begin
      --  We do not want to use lock on this read operation. State is marked
      --  as Atomic so that we ensure that the value retrieved is correct.

      return S.State;
   end Current_State;

   ---------------
   -- Set_False --
   ---------------

   procedure Set_False (S : in out Suspension_Object) is
      Result  : Interfaces.C.int;

   begin
      SSL.Abort_Defer.all;

      Result := pthread_mutex_lock (S.L'Access);
      pragma Assert (Result = 0);

      S.State := False;

      Result := pthread_mutex_unlock (S.L'Access);
      pragma Assert (Result = 0);

      SSL.Abort_Undefer.all;
   end Set_False;

   --------------
   -- Set_True --
   --------------

   procedure Set_True (S : in out Suspension_Object) is
      Result : Interfaces.C.int;

   begin
      SSL.Abort_Defer.all;

      Result := pthread_mutex_lock (S.L'Access);
      pragma Assert (Result = 0);

      --  If there is already a task waiting on this suspension object then
      --  we resume it, leaving the state of the suspension object to False,
      --  as it is specified in ARM D.10 par. 9. Otherwise, it just leaves
      --  the state to True.

      if S.Waiting then
         S.Waiting := False;
         S.State := False;

         Result := pthread_cond_signal (S.CV'Access);
         pragma Assert (Result = 0);

      else
         S.State := True;
      end if;

      Result := pthread_mutex_unlock (S.L'Access);
      pragma Assert (Result = 0);

      SSL.Abort_Undefer.all;
   end Set_True;

   ------------------------
   -- Suspend_Until_True --
   ------------------------

   procedure Suspend_Until_True (S : in out Suspension_Object) is
      Result : Interfaces.C.int;

   begin
      SSL.Abort_Defer.all;

      Result := pthread_mutex_lock (S.L'Access);
      pragma Assert (Result = 0);

      if S.Waiting then
         --  Program_Error must be raised upon calling Suspend_Until_True
         --  if another task is already waiting on that suspension object
         --  (ARM D.10 par. 10).

         Result := pthread_mutex_unlock (S.L'Access);
         pragma Assert (Result = 0);

         SSL.Abort_Undefer.all;

         raise Program_Error;
      else
         --  Suspend the task if the state is False. Otherwise, the task
         --  continues its execution, and the state of the suspension object
         --  is set to False (ARM D.10 par. 9).

         if S.State then
            S.State := False;
         else
            S.Waiting := True;

            loop
               --  Loop in case pthread_cond_wait returns earlier than expected
               --  (e.g. in case of EINTR caused by a signal).

               Result := pthread_cond_wait (S.CV'Access, S.L'Access);
               pragma Assert (Result = 0 or else Result = EINTR);

               exit when not S.Waiting;
            end loop;
         end if;

         Result := pthread_mutex_unlock (S.L'Access);
         pragma Assert (Result = 0);

         SSL.Abort_Undefer.all;
      end if;
   end Suspend_Until_True;

   ----------------
   -- Check_Exit --
   ----------------

   --  Dummy version

   function Check_Exit (Self_ID : ST.Task_Id) return Boolean is
      pragma Unreferenced (Self_ID);
   begin
      return True;
   end Check_Exit;

   --------------------
   -- Check_No_Locks --
   --------------------

   function Check_No_Locks (Self_ID : ST.Task_Id) return Boolean is
      pragma Unreferenced (Self_ID);
   begin
      return True;
   end Check_No_Locks;

   ----------------------
   -- Environment_Task --
   ----------------------

   function Environment_Task return Task_Id is
   begin
      return Environment_Task_Id;
   end Environment_Task;

   --------------
   -- Lock_RTS --
   --------------

   procedure Lock_RTS is
   begin
      Write_Lock (Single_RTS_Lock'Access, Global_Lock => True);
   end Lock_RTS;

   ----------------
   -- Unlock_RTS --
   ----------------

   procedure Unlock_RTS is
   begin
      Unlock (Single_RTS_Lock'Access, Global_Lock => True);
   end Unlock_RTS;

   ------------------
   -- Suspend_Task --
   ------------------

   function Suspend_Task
     (T           : ST.Task_Id;
      Thread_Self : Thread_Id) return Boolean
   is
      pragma Unreferenced (T);
      pragma Unreferenced (Thread_Self);
   begin
      return False;
   end Suspend_Task;

   -----------------
   -- Resume_Task --
   -----------------

   function Resume_Task
     (T           : ST.Task_Id;
      Thread_Self : Thread_Id) return Boolean
   is
      pragma Unreferenced (T);
      pragma Unreferenced (Thread_Self);
   begin
      return False;
   end Resume_Task;

   --------------------
   -- Stop_All_Tasks --
   --------------------

   procedure Stop_All_Tasks is
   begin
      null;
   end Stop_All_Tasks;

   ---------------
   -- Stop_Task --
   ---------------

   function Stop_Task (T : ST.Task_Id) return Boolean is
      pragma Unreferenced (T);
   begin
      return False;
   end Stop_Task;

   -------------------
   -- Continue_Task --
   -------------------

   function Continue_Task (T : ST.Task_Id) return Boolean is
      pragma Unreferenced (T);
   begin
      return False;
   end Continue_Task;

   ----------------
   -- Initialize --
   ----------------

   procedure Initialize (Environment_Task : Task_Id) is
      act     : aliased struct_sigaction;
      old_act : aliased struct_sigaction;
      Tmp_Set : aliased sigset_t;
      Result  : Interfaces.C.int;

      function State
        (Int : System.Interrupt_Management.Interrupt_ID) return Character;
      pragma Import (C, State, "__gnat_get_interrupt_state");
      --  Get interrupt state. Defined in a-init.c. The input argument is
      --  the interrupt number, and the result is one of the following:

      Default : constant Character := 's';
      --    'n'   this interrupt not set by any Interrupt_State pragma
      --    'u'   Interrupt_State pragma set state to User
      --    'r'   Interrupt_State pragma set state to Runtime
      --    's'   Interrupt_State pragma set state to System (use "default"
      --           system handler)

   begin
      Environment_Task_Id := Environment_Task;

      Interrupt_Management.Initialize;

      --  Initialize the lock used to synchronize chain of all ATCBs

      Initialize_Lock (Single_RTS_Lock'Access, RTS_Lock_Level);

      Specific.Initialize (Environment_Task);

      --  Make environment task known here because it doesn't go through
      --  Activate_Tasks, which does it for all other tasks.

      Known_Tasks (Known_Tasks'First) := Environment_Task;
      Environment_Task.Known_Tasks_Index := Known_Tasks'First;

      Enter_Task (Environment_Task);

      --  Install the abort-signal handler

      if State (System.Interrupt_Management.Abort_Task_Interrupt)
                                                     /= Default
      then
         act.sa_flags := 0;
         act.sa_handler := Abort_Handler'Address;

         Result := sigemptyset (Tmp_Set'Access);
         pragma Assert (Result = 0);
         act.sa_mask := Tmp_Set;

         Result :=
           sigaction (
             Signal (System.Interrupt_Management.Abort_Task_Interrupt),
             act'Unchecked_Access,
             old_act'Unchecked_Access);
         pragma Assert (Result = 0);
      end if;
   end Initialize;

   --  NOTE: Unlike other pthread implementations, we do *not* mask all
   --  signals here since we handle signals using the process-wide primitive
   --  signal, rather than using sigthreadmask and sigwait. The reason of
   --  this difference is that sigwait doesn't work when some critical
   --  signals (SIGABRT, SIGPIPE) are masked.

end System.Task_Primitives.Operations;