gcc/ada/s-parame.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                    S Y S T E M . P A R A M E T E R S                     --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                                                                          --
  10 --          Copyright (C) 1992-2001 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNAT was originally developed  by the GNAT team at  New York University. --
  31 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 --  This is the default version used for all systems for which no special
  36 --  target-specific version of this package is provided.
  37
  38 --  This package defines some system dependent parameters for GNAT. These
  39 --  are values that are referenced by the runtime library and are therefore
  40 --  relevant to the target machine.
  41
  42 --  The parameters whose value is defined in the spec are not generally
  43 --  expected to be changed. If they are changed, it will be necessary to
  44 --  recompile the run-time library.
  45
  46 --  The parameters which are defined by functions can be changed by modifying
  47 --  the body of System.Parameters in file s-parame.adb. A change to this body
  48 --  requires only rebinding and relinking of the application.
  49
  50 --  Note: do not introduce any pragma Inline statements into this unit, since
  51 --  otherwise the relinking and rebinding capability would be deactivated.
  52
  53 package System.Parameters is
  54 pragma Pure (Parameters);
  55
  56    ---------------------------------------
  57    -- Task And Stack Allocation Control --
  58    ---------------------------------------
  59
  60    type Task_Storage_Size is new Integer;
  61    --  Type used in tasking units for task storage size
  62
  63    type Size_Type is new Task_Storage_Size;
  64    --  Type used to provide task storage size to runtime
  65
  66    Unspecified_Size : constant Size_Type := Size_Type'First;
  67    --  Value used to indicate that no size type is set
  68
  69    subtype Ratio is Size_Type range -1 .. 100;
  70    Dynamic : constant Size_Type := -1;
  71    --  The secondary stack ratio is a constant between 0 and 100 which
  72    --  determines the percentage of the allocated task stack that is
  73    --  used by the secondary stack (the rest being the primary stack).
  74    --  The special value of minus one indicates that the secondary
  75    --  stack is to be allocated from the heap instead.
  76
  77    Sec_Stack_Ratio : constant Ratio := Dynamic;
  78    --  This constant defines the handling of the secondary stack
  79
  80    Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Ratio = Dynamic;
  81    --  Convenient Boolean for testing for dynamic secondary stack
  82
  83    function Default_Stack_Size return Size_Type;
  84    --  Default task stack size used if none is specified
  85
  86    function Minimum_Stack_Size return Size_Type;
  87    --  Minimum task stack size permitted
  88
  89    function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
  90    --  Given the storage size stored in the TCB, return the Storage_Size
  91    --  value required by the RM for the Storage_Size attribute. The
  92    --  required adjustment is as follows:
  93    --
  94    --    when Size = Unspecified_Size, return Default_Stack_Size
  95    --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
  96    --    otherwise return given Size
  97
  98    Stack_Grows_Down  : constant Boolean := True;
  99    --  This constant indicates whether the stack grows up (False) or
 100    --  down (True) in memory as functions are called. It is used for
 101    --  proper implementation of the stack overflow check.
 102
 103    ----------------------------------------------
 104    -- Characteristics of types in Interfaces.C --
 105    ----------------------------------------------
 106
 107    long_bits : constant := Long_Integer'Size;
 108    --  Number of bits in type long and unsigned_long. The normal convention
 109    --  is that this is the same as type Long_Integer, but this is not true
 110    --  of all targets. For example, in OpenVMS long /= Long_Integer.
 111
 112    ----------------------------------------------
 113    -- Behavior of Pragma Finalize_Storage_Only --
 114    ----------------------------------------------
 115
 116    --  Garbage_Collected is a Boolean constant whose value indicates the
 117    --  effect of the pragma Finalize_Storage_Entry on a controlled type.
 118
 119    --    Garbage_Collected = False
 120
 121    --      The system releases all storage on program termination only,
 122    --      but not other garbage collection occurs, so finalization calls
 123    --      are ommitted only for outer level onjects can be omitted if
 124    --      pragma Finalize_Storage_Only is used.
 125
 126    --    Garbage_Collected = True
 127
 128    --      The system provides full garbage collection, so it is never
 129    --      necessary to release storage for controlled objects for which
 130    --      a pragma Finalize_Storage_Only is used.
 131
 132    Garbage_Collected : constant Boolean := False;
 133    --  The storage mode for this system (release on program exit)
 134
 135    ---------------------
 136    -- Tasking Profile --
 137    ---------------------
 138
 139    --  In the following sections, constant parameters are defined to
 140    --  allow some optimizations within the tasking run time based on
 141    --  restrictions on the tasking features.
 142
 143    ----------------------
 144    -- Locking Strategy --
 145    ----------------------
 146
 147    Single_Lock : constant Boolean := False;
 148    --  Indicates whether a single lock should be used within the tasking
 149    --  run-time to protect internal structures. If True, a single lock
 150    --  will be used, meaning less locking/unlocking operations, but also
 151    --  more global contention. In general, Single_Lock should be set to
 152    --  True on single processor machines, and to False to multi-processor
 153    --  systems, but this can vary from application to application and also
 154    --  depends on the scheduling policy.
 155
 156    -------------------
 157    -- Task Abortion --
 158    -------------------
 159
 160    No_Abort : constant Boolean := False;
 161    --  This constant indicates whether abort statements and asynchronous
 162    --  transfer of control (ATC) are disallowed. If set to True, it is
 163    --  assumed that neither construct is used, and the run time does not
 164    --  need to defer/undefer abort and check for pending actions at
 165    --  completion points. A value of True for No_Abort corresponds to:
 166    --  pragma Restrictions (No_Abort_Statements);
 167    --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
 168
 169    ----------------------
 170    -- Dynamic Priority --
 171    ----------------------
 172
 173    Dynamic_Priority_Support : constant Boolean := True;
 174    --  This constant indicates whether dynamic changes of task priorities
 175    --  are allowed (True means normal RM mode in which such changes are
 176    --  allowed). In particular, if this is False, then we do not need to
 177    --  poll for pending base priority changes at every abort completion
 178    --  point. A value of False for Dynamic_Priority_Support corresponds
 179    --  to pragma Restrictions (No_Dynamic_Priorities);
 180
 181    --------------------
 182    -- Runtime Traces --
 183    --------------------
 184
 185    Runtime_Traces : constant Boolean := False;
 186    --  This constant indicates whether the runtime outputs traces to a
 187    --  predefined output or not (True means that traces are output).
 188    --  See System.Traces for more details.
 189
 190 end System.Parameters;