File : s-parame.ads
------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
5 -- S Y S T E M . P A R A M E T E R S --
-- --
-- S p e c --
-- --
-- $Revision: 1.45 $
10 -- --
-- Copyright (C) 1992-2001 Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- 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- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
20 -- Public License distributed with GNAT; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- 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, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
30 -- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
35
-- This is the default version used for all systems for which no special
-- target-specific version of this package is provided.
-- This package defines some system dependent parameters for GNAT. These
40 -- are values that are referenced by the runtime library and are therefore
-- relevant to the target machine.
-- The parameters whose value is defined in the spec are not generally
-- expected to be changed. If they are changed, it will be necessary to
45 -- recompile the run-time library.
-- The parameters which are defined by functions can be changed by modifying
-- the body of System.Parameters in file s-parame.adb. A change to this body
-- requires only rebinding and relinking of the application.
50
-- Note: do not introduce any pragma Inline statements into this unit, since
-- otherwise the relinking and rebinding capability would be deactivated.
package System.Parameters is
55 pragma Pure (Parameters);
---------------------------------------
-- Task And Stack Allocation Control --
---------------------------------------
60
type Task_Storage_Size is new Integer;
-- Type used in tasking units for task storage size
type Size_Type is new Task_Storage_Size;
65 -- Type used to provide task storage size to runtime
Unspecified_Size : constant Size_Type := Size_Type'First;
-- Value used to indicate that no size type is set
70 subtype Ratio is Size_Type range -1 .. 100;
Dynamic : constant Size_Type := -1;
-- The secondary stack ratio is a constant between 0 and 100 which
-- determines the percentage of the allocated task stack that is
-- used by the secondary stack (the rest being the primary stack).
75 -- The special value of minus one indicates that the secondary
-- stack is to be allocated from the heap instead.
Sec_Stack_Ratio : constant Ratio := Dynamic;
-- This constant defines the handling of the secondary stack
80
Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Ratio = Dynamic;
-- Convenient Boolean for testing for dynamic secondary stack
function Default_Stack_Size return Size_Type;
85 -- Default task stack size used if none is specified
function Minimum_Stack_Size return Size_Type;
-- Minimum task stack size permitted
90 function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
-- Given the storage size stored in the TCB, return the Storage_Size
-- value required by the RM for the Storage_Size attribute. The
-- required adjustment is as follows:
--
95 -- when Size = Unspecified_Size, return Default_Stack_Size
-- when Size < Minimum_Stack_Size, return Minimum_Stack_Size
-- otherwise return given Size
Stack_Grows_Down : constant Boolean := True;
100 -- This constant indicates whether the stack grows up (False) or
-- down (True) in memory as functions are called. It is used for
-- proper implementation of the stack overflow check.
----------------------------------------------
105 -- Characteristics of types in Interfaces.C --
----------------------------------------------
long_bits : constant := Long_Integer'Size;
-- Number of bits in type long and unsigned_long. The normal convention
110 -- is that this is the same as type Long_Integer, but this is not true
-- of all targets. For example, in OpenVMS long /= Long_Integer.
----------------------------------------------
-- Behavior of Pragma Finalize_Storage_Only --
115 ----------------------------------------------
-- Garbage_Collected is a Boolean constant whose value indicates the
-- effect of the pragma Finalize_Storage_Entry on a controlled type.
120 -- Garbage_Collected = False
-- The system releases all storage on program termination only,
-- but not other garbage collection occurs, so finalization calls
-- are ommitted only for outer level onjects can be omitted if
125 -- pragma Finalize_Storage_Only is used.
-- Garbage_Collected = True
-- The system provides full garbage collection, so it is never
130 -- necessary to release storage for controlled objects for which
-- a pragma Finalize_Storage_Only is used.
Garbage_Collected : constant Boolean := False;
-- The storage mode for this system (release on program exit)
135
---------------------
-- Tasking Profile --
---------------------
140 -- In the following sections, constant parameters are defined to
-- allow some optimizations within the tasking run time based on
-- restrictions on the tasking features.
----------------------
145 -- Locking Strategy --
----------------------
Single_Lock : constant Boolean := False;
-- Indicates whether a single lock should be used within the tasking
150 -- run-time to protect internal structures. If True, a single lock
-- will be used, meaning less locking/unlocking operations, but also
-- more global contention. In general, Single_Lock should be set to
-- True on single processor machines, and to False to multi-processor
-- systems, but this can vary from application to application and also
155 -- depends on the scheduling policy.
-------------------
-- Task Abortion --
-------------------
160
No_Abort : constant Boolean := False;
-- This constant indicates whether abort statements and asynchronous
-- transfer of control (ATC) are disallowed. If set to True, it is
-- assumed that neither construct is used, and the run time does not
165 -- need to defer/undefer abort and check for pending actions at
-- completion points. A value of True for No_Abort corresponds to:
-- pragma Restrictions (No_Abort_Statements);
-- pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
170 ----------------------
-- Dynamic Priority --
----------------------
Dynamic_Priority_Support : constant Boolean := True;
175 -- This constant indicates whether dynamic changes of task priorities
-- are allowed (True means normal RM mode in which such changes are
-- allowed). In particular, if this is False, then we do not need to
-- poll for pending base priority changes at every abort completion
-- point. A value of False for Dynamic_Priority_Support corresponds
180 -- to pragma Restrictions (No_Dynamic_Priorities);
--------------------
-- Runtime Traces --
--------------------
185
Runtime_Traces : constant Boolean := False;
-- This constant indicates whether the runtime outputs traces to a
-- predefined output or not (True means that traces are output).
-- See System.Traces for more details.
190
end System.Parameters;