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   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
   4 --                                                                          --
   5 --         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        --
   6 --                                                                          --
   7 --                                  S p e c                                 --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2009, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNARL was developed by the GNARL team at Florida State University.       --
  28 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package provides overall initialization of the tasking portion of the
  33 --  RTS. This package must be elaborated before any tasking features are used.
  34
  35 package System.Tasking.Initialization is
  36
  37    procedure Remove_From_All_Tasks_List (T : Task_Id);
  38    --  Remove T from All_Tasks_List. Call this function with RTS_Lock taken
  39
  40    ---------------------------------
  41    -- Tasking-Specific Soft Links --
  42    ---------------------------------
  43
  44    --  These permit us to leave out certain portions of the tasking
  45    --  run-time system if they are not used.  They are only used internally
  46    --  by the tasking run-time system.
  47
  48    --  So far, the only example is support for Ada.Task_Attributes
  49
  50    type Proc_T is access procedure (T : Task_Id);
  51
  52    procedure Finalize_Attributes (T : Task_Id);
  53    procedure Initialize_Attributes (T : Task_Id);
  54
  55    Finalize_Attributes_Link : Proc_T := Finalize_Attributes'Access;
  56    --  should be called with abort deferred and T.L write-locked
  57
  58    Initialize_Attributes_Link : Proc_T := Initialize_Attributes'Access;
  59    --  should be called with abort deferred, but holding no locks
  60
  61    -------------------------
  62    -- Abort Defer/Undefer --
  63    -------------------------
  64
  65    --  Defer_Abort defers the affects of low-level abort and priority change
  66    --  in the calling task until a matching Undefer_Abort call is executed.
  67
  68    --  Undefer_Abort DOES MORE than just undo the effects of one call to
  69    --  Defer_Abort. It is the universal "polling point" for deferred
  70    --  processing, including the following:
  71
  72    --  1) base priority changes
  73
  74    --  2) abort/ATC
  75
  76    --  Abort deferral MAY be nested (Self_ID.Deferral_Level is a count), but
  77    --  to avoid waste and undetected errors, it generally SHOULD NOT be
  78    --  nested. The symptom of over-deferring abort is that an exception may
  79    --  fail to be raised, or an abort may fail to take place.
  80
  81    --  Therefore, there are two sets of the inlineable defer/undefer routines,
  82    --  which are the ones to be used inside GNARL. One set allows nesting. The
  83    --  other does not. People who maintain the GNARL should try to avoid using
  84    --  the nested versions, or at least look very critically at the places
  85    --  where they are used.
  86
  87    --  In general, any GNARL call that is potentially blocking, or whose
  88    --  semantics require that it sometimes raise an exception, or that is
  89    --  required to be an abort completion point, must be made with abort
  90    --  Deferral_Level = 1.
  91
  92    --  In general, non-blocking GNARL calls, which may be made from inside a
  93    --  protected action, are likely to need to allow nested abort deferral.
  94
  95    --  With some critical exceptions (which are supposed to be documented),
  96    --  internal calls to the tasking runtime system assume abort is already
  97    --  deferred, and do not modify the deferral level.
  98
  99    --  There is also a set of non-inlineable defer/undefer routines, for direct
 100    --  call from the compiler. These are not inlineable because they may need
 101    --  to be called via pointers ("soft links"). For the sake of efficiency,
 102    --  the version with Self_ID as parameter should used wherever possible.
 103    --  These are all nestable.
 104
 105    --  Non-nestable inline versions
 106
 107    procedure Defer_Abort (Self_ID : Task_Id);
 108    pragma Inline (Defer_Abort);
 109
 110    procedure Undefer_Abort (Self_ID : Task_Id);
 111    pragma Inline (Undefer_Abort);
 112
 113    --  Nestable inline versions
 114
 115    procedure Defer_Abort_Nestable (Self_ID : Task_Id);
 116    pragma Inline (Defer_Abort_Nestable);
 117
 118    procedure Undefer_Abort_Nestable (Self_ID : Task_Id);
 119    pragma Inline (Undefer_Abort_Nestable);
 120
 121    procedure Do_Pending_Action (Self_ID : Task_Id);
 122    --  Only call with no locks, and when Self_ID.Pending_Action = True Perform
 123    --  necessary pending actions (e.g. abort, priority change). This procedure
 124    --  is usually called when needed as a result of calling Undefer_Abort,
 125    --  although in the case of e.g. No_Abort restriction, it can be necessary
 126    --  to force execution of pending actions.
 127
 128    function Check_Abort_Status return Integer;
 129    --  Returns Boolean'Pos (True) iff abort signal should raise
 130    --  Standard.Abort_Signal. Only used by IRIX currently.
 131
 132    --------------------------
 133    -- Change Base Priority --
 134    --------------------------
 135
 136    procedure Change_Base_Priority (T : Task_Id);
 137    --  Change the base priority of T. Has to be called with the affected
 138    --  task's ATCB write-locked. May temporarily release the lock.
 139
 140    ----------------------
 141    -- Task Lock/Unlock --
 142    ----------------------
 143
 144    procedure Task_Lock (Self_ID : Task_Id);
 145    pragma Inline (Task_Lock);
 146
 147    procedure Task_Unlock (Self_ID : Task_Id);
 148    pragma Inline (Task_Unlock);
 149    --  These are versions of Lock_Task and Unlock_Task created for use
 150    --  within the GNARL.
 151
 152    procedure Final_Task_Unlock (Self_ID : Task_Id);
 153    --  This version is only for use in Terminate_Task, when the task is
 154    --  relinquishing further rights to its own ATCB. There is a very
 155    --  interesting potential race condition there, where the old task may run
 156    --  concurrently with a new task that is allocated the old tasks (now
 157    --  reused) ATCB. The critical thing here is to not make any reference to
 158    --  the ATCB after the lock is released. See also comments on
 159    --  Terminate_Task and Unlock.
 160
 161    procedure Wakeup_Entry_Caller
 162      (Self_ID    : Task_Id;
 163       Entry_Call : Entry_Call_Link;
 164       New_State  : Entry_Call_State);
 165    pragma Inline (Wakeup_Entry_Caller);
 166    --  This is called at the end of service of an entry call, to abort the
 167    --  caller if he is in an abortable part, and to wake up the caller if he
 168    --  is on Entry_Caller_Sleep. Call it holding the lock of Entry_Call.Self.
 169    --
 170    --  Timed_Call or Simple_Call:
 171    --    The caller is waiting on Entry_Caller_Sleep, in Wait_For_Completion,
 172    --    or Wait_For_Completion_With_Timeout.
 173    --
 174    --  Conditional_Call:
 175    --    The caller might be in Wait_For_Completion,
 176    --    waiting for a rendezvous (possibly requeued without abort) to
 177    --    complete.
 178    --
 179    --  Asynchronous_Call:
 180    --    The caller may be executing in the abortable part an async. select,
 181    --    or on a time delay, if Entry_Call.State >= Was_Abortable.
 182
 183    procedure Locked_Abort_To_Level
 184      (Self_ID : Task_Id;
 185       T       : Task_Id;
 186       L       : ATC_Level);
 187    pragma Inline (Locked_Abort_To_Level);
 188    --  Abort a task to a specified ATC level. Call this only with T locked
 189
 190 end System.Tasking.Initialization;