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1 706 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT COMPILER COMPONENTS                         --
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--                                                                          --
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--                    S Y S T E M . P A R A M E T E R S                     --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--          Copyright (C) 1992-2011, Free Software Foundation, Inc.         --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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--                                                                          --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception,   --
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-- version 3.1, as published by the Free Software Foundation.               --
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--                                                                          --
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-- You should have received a copy of the GNU General Public License and    --
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-- a copy of the GCC Runtime Library Exception along with this program;     --
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-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
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-- <http://www.gnu.org/licenses/>.                                          --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This is the OpenVMS Alpha version
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--  This package defines some system dependent parameters for GNAT. These
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--  are values that are referenced by the runtime library and are therefore
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--  relevant to the target machine.
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--  The parameters whose value is defined in the spec are not generally
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--  expected to be changed. If they are changed, it will be necessary to
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--  recompile the run-time library.
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--  The parameters which are defined by functions can be changed by modifying
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--  the body of System.Parameters in file s-parame.adb. A change to this body
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--  requires only rebinding and relinking of the application.
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--  Note: do not introduce any pragma Inline statements into this unit, since
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--  otherwise the relinking and rebinding capability would be deactivated.
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package System.Parameters is
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   pragma Pure;
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   ---------------------------------------
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   -- Task And Stack Allocation Control --
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   ---------------------------------------
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   type Task_Storage_Size is new Integer;
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   --  Type used in tasking units for task storage size
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   type Size_Type is new Task_Storage_Size;
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   --  Type used to provide task storage size to runtime
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   Unspecified_Size : constant Size_Type := Size_Type'First;
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   --  Value used to indicate that no size type is set
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   subtype Percentage is Size_Type range -1 .. 100;
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   Dynamic : constant Size_Type := -1;
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   --  The secondary stack ratio is a constant between 0 and 100 which
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   --  determines the percentage of the allocated task stack that is
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   --  used by the secondary stack (the rest being the primary stack).
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   --  The special value of minus one indicates that the secondary
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   --  stack is to be allocated from the heap instead.
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   Sec_Stack_Percentage : constant Percentage := Dynamic;
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   --  This constant defines the handling of the secondary stack
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   Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Percentage = Dynamic;
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   --  Convenient Boolean for testing for dynamic secondary stack
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   function Default_Stack_Size return Size_Type;
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   --  Default task stack size used if none is specified
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   function Minimum_Stack_Size return Size_Type;
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   --  Minimum task stack size permitted
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   function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
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   --  Given the storage size stored in the TCB, return the Storage_Size
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   --  value required by the RM for the Storage_Size attribute. The
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   --  required adjustment is as follows:
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   --
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   --    when Size = Unspecified_Size, return Default_Stack_Size
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   --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
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   --    otherwise return given Size
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   Default_Env_Stack_Size : constant Size_Type := 8_192_000;
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   --  Assumed size of the environment task, if no other information
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   --  is available. This value is used when stack checking is
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   --  enabled and no GNAT_STACK_LIMIT environment variable is set.
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   Stack_Grows_Down  : constant Boolean := True;
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   --  This constant indicates whether the stack grows up (False) or
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   --  down (True) in memory as functions are called. It is used for
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   --  proper implementation of the stack overflow check.
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   ----------------------------------------------
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   -- Characteristics of types in Interfaces.C --
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   ----------------------------------------------
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   long_bits : constant := 32;
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   --  Number of bits in type long and unsigned_long. The normal convention
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   --  is that this is the same as type Long_Integer, but this is not true
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   --  of all targets. For example, in OpenVMS long /= Long_Integer.
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   ptr_bits  : constant := 32;
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   subtype C_Address is System.Address
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     range -2 ** (ptr_bits - 1) .. 2 ** (ptr_bits - 1) - 1;
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   for C_Address'Object_Size use ptr_bits;
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   --  Number of bits in Interfaces.C pointers, normally a standard address,
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   --  except on 64-bit VMS where they are 32-bit addresses, for compatibility
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   --  with legacy code. System.Aux_DEC.Short_Address can't be used because of
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   --  elaboration circularity.
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   C_Malloc_Linkname : constant String := "__gnat_malloc32";
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   --  Name of runtime function used to allocate such a pointer
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   ----------------------------------------------
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   -- Behavior of Pragma Finalize_Storage_Only --
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   ----------------------------------------------
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   --  Garbage_Collected is a Boolean constant whose value indicates the
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   --  effect of the pragma Finalize_Storage_Entry on a controlled type.
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   --    Garbage_Collected = False
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   --      The system releases all storage on program termination only,
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   --      but not other garbage collection occurs, so finalization calls
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   --      are omitted only for outer level objects can be omitted if
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   --      pragma Finalize_Storage_Only is used.
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   --    Garbage_Collected = True
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   --      The system provides full garbage collection, so it is never
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   --      necessary to release storage for controlled objects for which
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   --      a pragma Finalize_Storage_Only is used.
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   Garbage_Collected : constant Boolean := False;
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   --  The storage mode for this system (release on program exit)
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   ---------------------
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   -- Tasking Profile --
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   ---------------------
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   --  In the following sections, constant parameters are defined to
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   --  allow some optimizations and fine tuning within the tasking run time
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   --  based on restrictions on the tasking features.
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   ----------------------
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   -- Locking Strategy --
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   ----------------------
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   Single_Lock : constant Boolean := True;
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   --  Indicates whether a single lock should be used within the tasking
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   --  run-time to protect internal structures. If True, a single lock
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   --  will be used, meaning less locking/unlocking operations, but also
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   --  more global contention. In general, Single_Lock should be set to
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   --  True on single processor machines, and to False to multi-processor
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   --  systems, but this can vary from application to application and also
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   --  depends on the scheduling policy.
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   -------------------
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   -- Task Abortion --
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   -------------------
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   No_Abort : constant Boolean := False;
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   --  This constant indicates whether abort statements and asynchronous
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   --  transfer of control (ATC) are disallowed. If set to True, it is
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   --  assumed that neither construct is used, and the run time does not
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   --  need to defer/undefer abort and check for pending actions at
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   --  completion points. A value of True for No_Abort corresponds to:
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   --  pragma Restrictions (No_Abort_Statements);
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   --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
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   ---------------------
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   -- Task Attributes --
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   ---------------------
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   Default_Attribute_Count : constant := 4;
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   --  Number of pre-allocated Address-sized task attributes stored in the
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   --  task control block.
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   --------------------
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   -- Runtime Traces --
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   --------------------
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   Runtime_Traces : constant Boolean := False;
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   --  This constant indicates whether the runtime outputs traces to a
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   --  predefined output or not (True means that traces are output).
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   --  See System.Traces for more details.
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   -----------------------
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   -- Task Image Length --
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   -----------------------
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   Max_Task_Image_Length : constant := 256;
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   --  This constant specifies the maximum length of a task's image
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   ------------------------------
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   -- Exception Message Length --
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   ------------------------------
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   Default_Exception_Msg_Max_Length : constant := 512;
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   --  This constant specifies the maximum number of characters to allow in an
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   --  exception message (see RM 11.4.1(18)). The value for VMS exceeds the
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   --  default minimum of 200 to allow for the length of chained VMS condition
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   --  handling messages.
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end System.Parameters;

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