gcc/ada/s-tasini.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA 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 --                             $Revision: 1.24 $
  10 --                                                                          --
  11 --          Copyright (C) 1992-1999, Free Software Foundation, Inc.         --
  12 --                                                                          --
  13 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- As a special exception,  if other files  instantiate  generics from this --
  25 -- unit, or you link  this unit with other files  to produce an executable, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNARL was developed by the GNARL team at Florida State University. It is --
  32 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  33 -- State University (http://www.gnat.com).                                  --
  34 --                                                                          --
  35 ------------------------------------------------------------------------------
  36
  37 --  This package provides overall initialization of the tasking portion of the
  38 --  RTS. This package must be elaborated before any tasking features are used.
  39 --  It also contains initialization for Ada Task Control Block (ATCB) records.
  40
  41 package System.Tasking.Initialization is
  42
  43    procedure Remove_From_All_Tasks_List (T : Task_ID);
  44    --  Remove T from All_Tasks_List.
  45
  46    ------------------------------------------------
  47    -- Static (Compile-Time) Configuration Flags  --
  48    ------------------------------------------------
  49
  50    --  ?????
  51    --  Maybe this does not belong here?  Where else?
  52    --  For now, it is here because so is Change_Base_Priority,
  53    --  and the two are used together.
  54
  55    Dynamic_Priority_Support : constant Boolean := True;
  56    --  Should we poll for pending base priority changes at every
  57    --  abort completion point?
  58
  59    ---------------------------------
  60    -- Tasking-Specific Soft Links --
  61    ---------------------------------
  62
  63    --  These permit us to leave out certain portions of the tasking
  64    --  run-time system if they are not used.  They are only used internally
  65    --  by the tasking run-time system.
  66    --  So far, the only example is support for Ada.Task_Attributes.
  67
  68    type Proc_T is access procedure (T : Task_ID);
  69
  70    procedure Finalize_Attributes (T : Task_ID);
  71    procedure Initialize_Attributes (T : Task_ID);
  72
  73    Finalize_Attributes_Link : Proc_T := Finalize_Attributes'Access;
  74    --  should be called with abortion deferred and T.L write-locked
  75
  76    Initialize_Attributes_Link : Proc_T := Initialize_Attributes'Access;
  77    --  should be called with abortion deferred, but holding no locks
  78
  79    -------------------------
  80    -- Abort Defer/Undefer --
  81    -------------------------
  82
  83    --  Defer_Abort defers the affects of low-level abort and priority change
  84    --  in the calling task until a matching Undefer_Abort call is executed.
  85
  86    --  Undefer_Abort DOES MORE than just undo the effects of one call to
  87    --  Defer_Abort.  It is the universal "polling point" for deferred
  88    --  processing, including the following:
  89
  90    --  1) base priority changes
  91
  92    --  2) exceptions that need to be raised
  93
  94    --  3) abort/ATC
  95
  96    --  Abort deferral MAY be nested (Self_ID.Deferral_Level is a count),
  97    --  but to avoid waste and undetected errors, it generally SHOULD NOT
  98    --  be nested.  The symptom of over-deferring abort is that an exception
  99    --  may fail to be raised, or an abort may fail to take place.
 100
 101    --  Therefore, there are two sets of the inlinable defer/undefer
 102    --  routines, which are the ones to be used inside GNARL.
 103    --  One set allows nesting.  The other does not.  People who
 104    --  maintain the GNARL should try to avoid using the nested versions,
 105    --  or at least look very critically at the places where they are
 106    --  used.
 107
 108    --  In general, any GNARL call that is potentially blocking, or
 109    --  whose semantics require that it sometimes raise an exception,
 110    --  or that is required to be an abort completion point, must be
 111    --  made with abort Deferral_Level = 1.
 112
 113    --  In general, non-blocking GNARL calls, which may be made from inside
 114    --  a protected action, are likely to need to allow nested abort
 115    --  deferral.
 116
 117    --  With some critical exceptions (which are supposed to be documented),
 118    --  internal calls to the tasking runtime system assume abort is already
 119    --  deferred, and do not modify the deferral level.
 120
 121    --  There is also a set of non-linable defer/undefer routines,
 122    --  for direct call from the compiler.  These are not in-lineable
 123    --  because they may need to be called via pointers ("soft links").
 124    --  For the sake of efficiency, the version with Self_ID as parameter
 125    --  should used wherever possible.  These are all nestable.
 126
 127    --  Non-nestable inline versions  --
 128
 129    procedure Defer_Abort (Self_ID : Task_ID);
 130    pragma Inline (Defer_Abort);
 131
 132    procedure Undefer_Abort (Self_ID : Task_ID);
 133    pragma Inline (Undefer_Abort);
 134
 135    --  Nestable inline versions  --
 136
 137    procedure Defer_Abort_Nestable (Self_ID : Task_ID);
 138    pragma Inline (Defer_Abort_Nestable);
 139
 140    procedure Undefer_Abort_Nestable (Self_ID : Task_ID);
 141    pragma Inline (Undefer_Abort_Nestable);
 142
 143    --  NON-INLINE versions without Self_ID for code generated by the
 144    --  expander and for hard links
 145
 146    procedure Defer_Abortion;
 147    procedure Undefer_Abortion;
 148
 149    --  ?????
 150    --  Try to phase out all uses of the above versions.
 151
 152    function Check_Abort_Status return Integer;
 153    --  Returns Boolean'Pos (True) iff abort signal should raise
 154    --  Standard.Abort_Signal. Only used by IRIX currently.
 155
 156    ---------------------------
 157    --  Change Base Priority --
 158    ---------------------------
 159
 160    procedure Change_Base_Priority (T : Task_ID);
 161    --  Change the base priority of T.
 162    --  Has to be called with the affected task's ATCB write-locked.
 163    --  May temporariliy release the lock.
 164
 165    procedure Poll_Base_Priority_Change (Self_ID : Task_ID);
 166    --  Has to be called with Self_ID's ATCB write-locked.
 167    --  May temporariliy release the lock.
 168    pragma Inline (Poll_Base_Priority_Change);
 169
 170    ----------------------
 171    -- Task Lock/Unlock --
 172    ----------------------
 173
 174    procedure Task_Lock (Self_ID : Task_ID);
 175    procedure Task_Unlock (Self_ID : Task_ID);
 176    --  These are versions of Lock_Task and Unlock_Task created for use
 177    --  within the GNARL.
 178
 179    procedure Final_Task_Unlock (Self_ID : Task_ID);
 180    --  This version is only for use in Terminate_Task, when the task
 181    --  is relinquishing further rights to its own ATCB.
 182    --  There is a very interesting potential race condition there, where
 183    --  the old task may run concurrently with a new task that is allocated
 184    --  the old tasks (now reused) ATCB.  The critical thing here is to
 185    --  not make any reference to the ATCB after the lock is released.
 186    --  See also comments on Terminate_Task and Unlock.
 187
 188    procedure Wakeup_Entry_Caller
 189      (Self_ID    : Task_ID;
 190       Entry_Call : Entry_Call_Link;
 191       New_State  : Entry_Call_State);
 192    pragma Inline (Wakeup_Entry_Caller);
 193    --  This is called at the end of service of an entry call,
 194    --  to abort the caller if he is in an abortable part, and
 195    --  to wake up the caller if he is on Entry_Caller_Sleep.
 196    --  Call it holding the lock of Entry_Call.Self.
 197    --
 198    --  Timed_Call or Simple_Call:
 199    --    The caller is waiting on Entry_Caller_Sleep, in
 200    --    Wait_For_Completion, or Wait_For_Completion_With_Timeout.
 201    --
 202    --  Conditional_Call:
 203    --    The caller might be in Wait_For_Completion,
 204    --    waiting for a rendezvous (possibly requeued without abort)
 205    --    to complete.
 206    --
 207    --  Asynchronous_Call:
 208    --    The caller may be executing in the abortable part o
 209    --    an async. select, or on a time delay,
 210    --    if Entry_Call.State >= Was_Abortable.
 211
 212    procedure Locked_Abort_To_Level
 213      (Self_ID : Task_ID;
 214       T       : Task_ID;
 215       L       : ATC_Level);
 216    pragma Inline (Locked_Abort_To_Level);
 217    --  Abort a task to a specified ATC level.
 218    --  Call this only with T locked.
 219
 220 end System.Tasking.Initialization;