gcc/ada/5zparame.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 --          Copyright (C) 1992-2003 Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- GNAT 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 2,  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.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This is the default VxWorks version of the package.`
  35
  36 --  This package defines some system dependent parameters for GNAT. These
  37 --  are values that are referenced by the runtime library and are therefore
  38 --  relevant to the target machine.
  39
  40 --  The parameters whose value is defined in the spec are not generally
  41 --  expected to be changed. If they are changed, it will be necessary to
  42 --  recompile the run-time library.
  43
  44 --  The parameters which are defined by functions can be changed by modifying
  45 --  the body of System.Parameters in file s-parame.adb. A change to this body
  46 --  requires only rebinding and relinking of the application.
  47
  48 --  Note: do not introduce any pragma Inline statements into this unit, since
  49 --  otherwise the relinking and rebinding capability would be deactivated.
  50
  51 package System.Parameters is
  52 pragma Pure (Parameters);
  53
  54    ---------------------------------------
  55    -- Task And Stack Allocation Control --
  56    ---------------------------------------
  57
  58    type Task_Storage_Size is new Integer;
  59    --  Type used in tasking units for task storage size
  60
  61    type Size_Type is new Task_Storage_Size;
  62    --  Type used to provide task storage size to runtime
  63
  64    Unspecified_Size : constant Size_Type := Size_Type'First;
  65    --  Value used to indicate that no size type is set
  66
  67    subtype Ratio is Size_Type range -1 .. 100;
  68    Dynamic : constant Size_Type := -1;
  69    --  The secondary stack ratio is a constant between 0 and 100 which
  70    --  determines the percentage of the allocated task stack that is
  71    --  used by the secondary stack (the rest being the primary stack).
  72    --  The special value of minus one indicates that the secondary
  73    --  stack is to be allocated from the heap instead.
  74
  75    Sec_Stack_Ratio : constant Ratio := Dynamic;
  76    --  This constant defines the handling of the secondary stack
  77
  78    Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Ratio = Dynamic;
  79    --  Convenient Boolean for testing for dynamic secondary stack
  80
  81    function Default_Stack_Size return Size_Type;
  82    --  Default task stack size used if none is specified
  83
  84    function Minimum_Stack_Size return Size_Type;
  85    --  Minimum task stack size permitted
  86
  87    function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
  88    --  Given the storage size stored in the TCB, return the Storage_Size
  89    --  value required by the RM for the Storage_Size attribute. The
  90    --  required adjustment is as follows:
  91    --
  92    --    when Size = Unspecified_Size, return Default_Stack_Size
  93    --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
  94    --    otherwise return given Size
  95
  96    Default_Env_Stack_Size : constant Size_Type := 14_336;
  97    --  Assumed size of the environment task, if no other information
  98    --  is available. This value is used when stack checking is
  99    --  enabled and no GNAT_STACK_LIMIT environment variable is set.
 100    --  This value is chosen as the VxWorks default stack size is 20kB,
 101    --  and a little more than 4kB is necessary for the run time.
 102
 103    Stack_Grows_Down  : constant Boolean := True;
 104    --  This constant indicates whether the stack grows up (False) or
 105    --  down (True) in memory as functions are called. It is used for
 106    --  proper implementation of the stack overflow check.
 107
 108    ----------------------------------------------
 109    -- Characteristics of types in Interfaces.C --
 110    ----------------------------------------------
 111
 112    long_bits : constant := Long_Integer'Size;
 113    --  Number of bits in type long and unsigned_long. The normal convention
 114    --  is that this is the same as type Long_Integer, but this is not true
 115    --  of all targets. For example, in OpenVMS long /= Long_Integer.
 116
 117    ----------------------------------------------
 118    -- Behavior of Pragma Finalize_Storage_Only --
 119    ----------------------------------------------
 120
 121    --  Garbage_Collected is a Boolean constant whose value indicates the
 122    --  effect of the pragma Finalize_Storage_Entry on a controlled type.
 123
 124    --    Garbage_Collected = False
 125
 126    --      The system releases all storage on program termination only,
 127    --      but not other garbage collection occurs, so finalization calls
 128    --      are ommitted only for outer level onjects can be omitted if
 129    --      pragma Finalize_Storage_Only is used.
 130
 131    --    Garbage_Collected = True
 132
 133    --      The system provides full garbage collection, so it is never
 134    --      necessary to release storage for controlled objects for which
 135    --      a pragma Finalize_Storage_Only is used.
 136
 137    Garbage_Collected : constant Boolean := False;
 138    --  The storage mode for this system (release on program exit)
 139
 140    ---------------------
 141    -- Tasking Profile --
 142    ---------------------
 143
 144    --  In the following sections, constant parameters are defined to
 145    --  allow some optimizations and fine tuning within the tasking run time
 146    --  based on restrictions on the tasking features.
 147
 148    ----------------------
 149    -- Locking Strategy --
 150    ----------------------
 151
 152    Single_Lock : constant Boolean := False;
 153    --  Indicates whether a single lock should be used within the tasking
 154    --  run-time to protect internal structures. If True, a single lock
 155    --  will be used, meaning less locking/unlocking operations, but also
 156    --  more global contention. In general, Single_Lock should be set to
 157    --  True on single processor machines, and to False to multi-processor
 158    --  systems, but this can vary from application to application and also
 159    --  depends on the scheduling policy.
 160
 161    -------------------
 162    -- Task Abortion --
 163    -------------------
 164
 165    No_Abort : constant Boolean := False;
 166    --  This constant indicates whether abort statements and asynchronous
 167    --  transfer of control (ATC) are disallowed. If set to True, it is
 168    --  assumed that neither construct is used, and the run time does not
 169    --  need to defer/undefer abort and check for pending actions at
 170    --  completion points. A value of True for No_Abort corresponds to:
 171    --  pragma Restrictions (No_Abort_Statements);
 172    --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
 173
 174    ----------------------
 175    -- Dynamic Priority --
 176    ----------------------
 177
 178    Dynamic_Priority_Support : constant Boolean := True;
 179    --  This constant indicates whether dynamic changes of task priorities
 180    --  are allowed (True means normal RM mode in which such changes are
 181    --  allowed). In particular, if this is False, then we do not need to
 182    --  poll for pending base priority changes at every abort completion
 183    --  point. A value of False for Dynamic_Priority_Support corresponds
 184    --  to pragma Restrictions (No_Dynamic_Priorities);
 185
 186    ---------------------
 187    -- Task Attributes --
 188    ---------------------
 189
 190    Default_Attribute_Count : constant := 4;
 191    --  Number of pre-allocated Address-sized task attributes stored in the
 192    --  task control block.
 193
 194    --------------------
 195    -- Runtime Traces --
 196    --------------------
 197
 198    Runtime_Traces : constant Boolean := False;
 199    --  This constant indicates whether the runtime outputs traces to a
 200    --  predefined output or not (True means that traces are output).
 201    --  See System.Traces for more details.
 202
 203 end System.Parameters;