------------------------------------------------------------------------------
--                                                                          --
--                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
--                                                                          --
--         S Y S T E M . T A S K I N G . I N I T I A L I Z A T I O N        --
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--                             $Revision: 1.24 $
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------------------------------------------------------------------------------

--  This package provides overall initialization of the tasking portion of the
--  RTS. This package must be elaborated before any tasking features are used.
--  It also contains initialization for Ada Task Control Block (ATCB) records.

package System.Tasking.Initialization is

   procedure Remove_From_All_Tasks_List (T : Task_ID);
   --  Remove T from All_Tasks_List.

   ------------------------------------------------
   -- Static (Compile-Time) Configuration Flags  --
   ------------------------------------------------

   --  ?????
   --  Maybe this does not belong here?  Where else?
   --  For now, it is here because so is Change_Base_Priority,
   --  and the two are used together.

   Dynamic_Priority_Support : constant Boolean := True;
   --  Should we poll for pending base priority changes at every
   --  abort completion point?

   ---------------------------------
   -- Tasking-Specific Soft Links --
   ---------------------------------

   --  These permit us to leave out certain portions of the tasking
   --  run-time system if they are not used.  They are only used internally
   --  by the tasking run-time system.
   --  So far, the only example is support for Ada.Task_Attributes.

   type Proc_T is access procedure (T : Task_ID);

   procedure Finalize_Attributes (T : Task_ID);
   procedure Initialize_Attributes (T : Task_ID);

   Finalize_Attributes_Link : Proc_T := Finalize_Attributes'Access;
   --  should be called with abortion deferred and T.L write-locked

   Initialize_Attributes_Link : Proc_T := Initialize_Attributes'Access;
   --  should be called with abortion deferred, but holding no locks

   -------------------------
   -- Abort Defer/Undefer --
   -------------------------

   --  Defer_Abort defers the affects of low-level abort and priority change
   --  in the calling task until a matching Undefer_Abort call is executed.

   --  Undefer_Abort DOES MORE than just undo the effects of one call to
   --  Defer_Abort.  It is the universal "polling point" for deferred
   --  processing, including the following:

   --  1) base priority changes

   --  2) exceptions that need to be raised

   --  3) abort/ATC

   --  Abort deferral MAY be nested (Self_ID.Deferral_Level is a count),
   --  but to avoid waste and undetected errors, it generally SHOULD NOT
   --  be nested.  The symptom of over-deferring abort is that an exception
   --  may fail to be raised, or an abort may fail to take place.

   --  Therefore, there are two sets of the inlinable defer/undefer
   --  routines, which are the ones to be used inside GNARL.
   --  One set allows nesting.  The other does not.  People who
   --  maintain the GNARL should try to avoid using the nested versions,
   --  or at least look very critically at the places where they are
   --  used.

   --  In general, any GNARL call that is potentially blocking, or
   --  whose semantics require that it sometimes raise an exception,
   --  or that is required to be an abort completion point, must be
   --  made with abort Deferral_Level = 1.

   --  In general, non-blocking GNARL calls, which may be made from inside
   --  a protected action, are likely to need to allow nested abort
   --  deferral.

   --  With some critical exceptions (which are supposed to be documented),
   --  internal calls to the tasking runtime system assume abort is already
   --  deferred, and do not modify the deferral level.

   --  There is also a set of non-linable defer/undefer routines,
   --  for direct call from the compiler.  These are not in-lineable
   --  because they may need to be called via pointers ("soft links").
   --  For the sake of efficiency, the version with Self_ID as parameter
   --  should used wherever possible.  These are all nestable.

   --  Non-nestable inline versions  --

   procedure Defer_Abort (Self_ID : Task_ID);
   pragma Inline (Defer_Abort);

   procedure Undefer_Abort (Self_ID : Task_ID);
   pragma Inline (Undefer_Abort);

   --  Nestable inline versions  --

   procedure Defer_Abort_Nestable (Self_ID : Task_ID);
   pragma Inline (Defer_Abort_Nestable);

   procedure Undefer_Abort_Nestable (Self_ID : Task_ID);
   pragma Inline (Undefer_Abort_Nestable);

   --  NON-INLINE versions without Self_ID for code generated by the
   --  expander and for hard links

   procedure Defer_Abortion;
   procedure Undefer_Abortion;

   --  ?????
   --  Try to phase out all uses of the above versions.

   function Check_Abort_Status return Integer;
   --  Returns Boolean'Pos (True) iff abort signal should raise
   --  Standard.Abort_Signal. Only used by IRIX currently.

   ---------------------------
   --  Change Base Priority --
   ---------------------------

   procedure Change_Base_Priority (T : Task_ID);
   --  Change the base priority of T.
   --  Has to be called with the affected task's ATCB write-locked.
   --  May temporariliy release the lock.

   procedure Poll_Base_Priority_Change (Self_ID : Task_ID);
   --  Has to be called with Self_ID's ATCB write-locked.
   --  May temporariliy release the lock.
   pragma Inline (Poll_Base_Priority_Change);

   ----------------------
   -- Task Lock/Unlock --
   ----------------------

   procedure Task_Lock (Self_ID : Task_ID);
   procedure Task_Unlock (Self_ID : Task_ID);
   --  These are versions of Lock_Task and Unlock_Task created for use
   --  within the GNARL.

   procedure Final_Task_Unlock (Self_ID : Task_ID);
   --  This version is only for use in Terminate_Task, when the task
   --  is relinquishing further rights to its own ATCB.
   --  There is a very interesting potential race condition there, where
   --  the old task may run concurrently with a new task that is allocated
   --  the old tasks (now reused) ATCB.  The critical thing here is to
   --  not make any reference to the ATCB after the lock is released.
   --  See also comments on Terminate_Task and Unlock.

   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.
   --
   --  Conditional_Call:
   --    The caller might be in Wait_For_Completion,
   --    waiting for a rendezvous (possibly requeued without abort)
   --    to complete.
   --
   --  Asynchronous_Call:
   --    The caller may be executing in the abortable part o
   --    an async. select, or on a time delay,
   --    if Entry_Call.State >= Was_Abortable.

   procedure Locked_Abort_To_Level
     (Self_ID : Task_ID;
      T       : Task_ID;
      L       : ATC_Level);
   pragma Inline (Locked_Abort_To_Level);
   --  Abort a task to a specified ATC level.
   --  Call this only with T locked.

end System.Tasking.Initialization;
