------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- S Y S T E M . S H A R E D _ M E M O R Y --
-- --
-- B o d y --
-- --
-- Copyright (C) 1998-2023, 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- --
-- ware Foundation; either version 3, 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. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
with Ada.IO_Exceptions;
with Ada.Streams;
with Ada.Streams.Stream_IO;
with System.Global_Locks;
with System.Soft_Links;
with System.CRTL;
with System.File_Control_Block;
with System.File_IO;
with System.HTable;
with Ada.Unchecked_Deallocation;
with Ada.Unchecked_Conversion;
package body System.Shared_Storage is
package AS renames Ada.Streams;
package IOX renames Ada.IO_Exceptions;
package FCB renames System.File_Control_Block;
package SFI renames System.File_IO;
package SIO renames Ada.Streams.Stream_IO;
type String_Access is access String;
procedure Free is new Ada.Unchecked_Deallocation
(Object => String, Name => String_Access);
Dir : String_Access;
-- Holds the directory
------------------------------------------------
-- Variables for Shared Variable Access Files --
------------------------------------------------
Max_Shared_Var_Files : constant := 20;
-- Maximum number of lock files that can be open
Shared_Var_Files_Open : Natural := 0;
-- Number of shared variable access files currently open
type File_Stream_Type is new AS.Root_Stream_Type with record
File : SIO.File_Type;
end record;
type File_Stream_Access is access all File_Stream_Type'Class;
procedure Read
(Stream : in out File_Stream_Type;
Item : out AS.Stream_Element_Array;
Last : out AS.Stream_Element_Offset);
procedure Write
(Stream : in out File_Stream_Type;
Item : AS.Stream_Element_Array);
subtype Hash_Header is Natural range 0 .. 30;
-- Number of hash headers, related (for efficiency purposes only) to the
-- maximum number of lock files.
type Shared_Var_File_Entry;
type Shared_Var_File_Entry_Ptr is access Shared_Var_File_Entry;
type Shared_Var_File_Entry is record
Name : String_Access;
-- Name of variable, as passed to Read_File/Write_File routines
Stream : File_Stream_Access;
-- Stream_IO file for the shared variable file
Next : Shared_Var_File_Entry_Ptr;
Prev : Shared_Var_File_Entry_Ptr;
-- Links for LRU chain
end record;
procedure Free is new Ada.Unchecked_Deallocation
(Object => Shared_Var_File_Entry,
Name => Shared_Var_File_Entry_Ptr);
procedure Free is new Ada.Unchecked_Deallocation
(Object => File_Stream_Type'Class,
Name => File_Stream_Access);
function To_AFCB_Ptr is
new Ada.Unchecked_Conversion (SIO.File_Type, FCB.AFCB_Ptr);
LRU_Head : Shared_Var_File_Entry_Ptr;
LRU_Tail : Shared_Var_File_Entry_Ptr;
-- As lock files are opened, they are organized into a least recently
-- used chain, which is a doubly linked list using the Next and Prev
-- fields of Shared_Var_File_Entry records. The field LRU_Head points
-- to the least recently used entry, whose prev pointer is null, and
-- LRU_Tail points to the most recently used entry, whose next pointer
-- is null. These pointers are null only if the list is empty.
function Hash (F : String_Access) return Hash_Header;
function Equal (F1, F2 : String_Access) return Boolean;
-- Hash and equality functions for hash table
package SFT is new System.HTable.Simple_HTable
(Header_Num => Hash_Header,
Element => Shared_Var_File_Entry_Ptr,
No_Element => null,
Key => String_Access,
Hash => Hash,
Equal => Equal);
--------------------------------
-- Variables for Lock Control --
--------------------------------
Global_Lock : Global_Locks.Lock_Type;
Lock_Count : Natural := 0;
-- Counts nesting of lock calls, 0 means lock is not held
-----------------------
-- Local Subprograms --
-----------------------
procedure Initialize;
-- Called to initialize data structures for this package.
-- Has no effect except on the first call.
procedure Enter_SFE (SFE : Shared_Var_File_Entry_Ptr; Fname : String);
-- The first parameter is a pointer to a newly allocated SFE, whose
-- File field is already set appropriately. Fname is the name of the
-- variable as passed to Shared_Var_RFile/Shared_Var_WFile. Enter_SFE
-- completes the SFE value, and enters it into the hash table. If the
-- hash table is already full, the least recently used entry is first
-- closed and discarded.
function Retrieve (File : String) return Shared_Var_File_Entry_Ptr;
-- Given a file name, this function searches the hash table to see if
-- the file is currently open. If so, then a pointer to the already
-- created entry is returned, after first moving it to the head of
-- the LRU chain. If not, then null is returned.
function Shared_Var_ROpen (Var : String) return SIO.Stream_Access;
-- As described above, this routine returns null if the
-- corresponding shared storage does not exist, and otherwise, if
-- the storage does exist, a Stream_Access value that references
-- the shared storage, ready to read the current value.
function Shared_Var_WOpen (Var : String) return SIO.Stream_Access;
-- As described above, this routine returns a Stream_Access value
-- that references the shared storage, ready to write the new
-- value. The storage is created by this call if it does not
-- already exist.
procedure Shared_Var_Close (Var : SIO.Stream_Access);
-- This routine signals the end of a read/assign operation. It can
-- be useful to embrace a read/write operation between a call to
-- open and a call to close which protect the whole operation.
-- Otherwise, two simultaneous operations can result in the
-- raising of exception Data_Error by setting the access mode of
-- the variable in an incorrect mode.
---------------
-- Enter_SFE --
---------------
procedure Enter_SFE (SFE : Shared_Var_File_Entry_Ptr; Fname : String) is
Freed : Shared_Var_File_Entry_Ptr;
begin
SFE.Name := new String'(Fname);
-- Release least recently used entry if we have to
if Shared_Var_Files_Open = Max_Shared_Var_Files then
Freed := LRU_Head;
if Freed.Next /= null then
Freed.Next.Prev := null;
end if;
LRU_Head := Freed.Next;
SFT.Remove (Freed.Name);
SIO.Close (Freed.Stream.File);
Free (Freed.Name);
Free (Freed.Stream);
Free (Freed);
else
Shared_Var_Files_Open := Shared_Var_Files_Open + 1;
end if;
-- Add new entry to hash table
SFT.Set (SFE.Name, SFE);
-- Add new entry at end of LRU chain
if LRU_Head = null then
LRU_Head := SFE;
LRU_Tail := SFE;
else
SFE.Prev := LRU_Tail;
LRU_Tail.Next := SFE;
LRU_Tail := SFE;
end if;
end Enter_SFE;
-----------
-- Equal --
-----------
function Equal (F1, F2 : String_Access) return Boolean is
begin
return F1.all = F2.all;
end Equal;
----------
-- Hash --
----------
function Hash (F : String_Access) return Hash_Header is
N : Natural := 0;
begin
-- Add up characters of name, mod our table size
for J in F'Range loop
N := (N + Character'Pos (F (J))) mod (Hash_Header'Last + 1);
end loop;
return N;
end Hash;
----------------
-- Initialize --
----------------
procedure Initialize is
procedure Get_Env_Value_Ptr (Name, Length, Ptr : Address);
pragma Import (C, Get_Env_Value_Ptr, "__gnat_getenv");
subtype size_t is CRTL.size_t;
procedure Strncpy (dest, src : System.Address; n : size_t)
renames CRTL.strncpy;
Dir_Name : aliased constant String :=
"SHARED_MEMORY_DIRECTORY" & ASCII.NUL;
Env_Value_Ptr : aliased Address;
Env_Value_Len : aliased Integer;
begin
if Dir = null then
Get_Env_Value_Ptr
(Dir_Name'Address, Env_Value_Len'Address, Env_Value_Ptr'Address);
Dir := new String (1 .. Env_Value_Len);
if Env_Value_Len > 0 then
Strncpy (Dir.all'Address, Env_Value_Ptr, size_t (Env_Value_Len));
end if;
System.Global_Locks.Create_Lock (Global_Lock, Dir.all & "__lock");
end if;
end Initialize;
----------
-- Read --
----------
procedure Read
(Stream : in out File_Stream_Type;
Item : out AS.Stream_Element_Array;
Last : out AS.Stream_Element_Offset)
is
begin
SIO.Read (Stream.File, Item, Last);
exception when others =>
Last := Item'Last;
end Read;
--------------
-- Retrieve --
--------------
function Retrieve (File : String) return Shared_Var_File_Entry_Ptr is
SFE : Shared_Var_File_Entry_Ptr;
begin
Initialize;
SFE := SFT.Get (File'Unrestricted_Access);
if SFE /= null then
-- Move to head of LRU chain
if SFE = LRU_Tail then
null;
elsif SFE = LRU_Head then
LRU_Head := LRU_Head.Next;
LRU_Head.Prev := null;
else
SFE.Next.Prev := SFE.Prev;
SFE.Prev.Next := SFE.Next;
end if;
SFE.Next := null;
SFE.Prev := LRU_Tail;
LRU_Tail.Next := SFE;
LRU_Tail := SFE;
end if;
return SFE;
end Retrieve;
----------------------
-- Shared_Var_Close --
----------------------
procedure Shared_Var_Close (Var : SIO.Stream_Access) is
pragma Warnings (Off, Var);
begin
System.Soft_Links.Unlock_Task.all;
end Shared_Var_Close;
---------------------
-- Shared_Var_Lock --
---------------------
procedure Shared_Var_Lock (Var : String) is
pragma Warnings (Off, Var);
begin
System.Soft_Links.Lock_Task.all;
Initialize;
if Lock_Count /= 0 then
Lock_Count := Lock_Count + 1;
System.Soft_Links.Unlock_Task.all;
else
Lock_Count := 1;
System.Soft_Links.Unlock_Task.all;
System.Global_Locks.Acquire_Lock (Global_Lock);
end if;
exception
when others =>
System.Soft_Links.Unlock_Task.all;
raise;
end Shared_Var_Lock;
----------------------
-- Shared_Var_Procs --
----------------------
package body Shared_Var_Procs is
use type SIO.Stream_Access;
----------
-- Read --
----------
procedure Read is
S : SIO.Stream_Access := null;
begin
S := Shared_Var_ROpen (Full_Name);
if S /= null then
Typ'Read (S, V);
Shared_Var_Close (S);
end if;
end Read;
------------
-- Write --
------------
procedure Write is
S : SIO.Stream_Access := null;
begin
S := Shared_Var_WOpen (Full_Name);
Typ'Write (S, V);
Shared_Var_Close (S);
return;
end Write;
end Shared_Var_Procs;
----------------------
-- Shared_Var_ROpen --
----------------------
function Shared_Var_ROpen (Var : String) return SIO.Stream_Access is
SFE : Shared_Var_File_Entry_Ptr;
use type Ada.Streams.Stream_IO.File_Mode;
begin
System.Soft_Links.Lock_Task.all;
SFE := Retrieve (Var);
-- Here if file is not already open, try to open it
if SFE = null then
declare
S : aliased constant String := Dir.all & Var;
begin
SFE := new Shared_Var_File_Entry;
SFE.Stream := new File_Stream_Type;
SIO.Open (SFE.Stream.File, SIO.In_File, Name => S);
SFI.Make_Unbuffered (To_AFCB_Ptr (SFE.Stream.File));
-- File opened successfully, put new entry in hash table. Note
-- that in this case, file is positioned correctly for read.
Enter_SFE (SFE, Var);
exception
-- If we get an exception, it means that the file does not
-- exist, and in this case, we don't need the SFE and we
-- return null;
when IOX.Name_Error =>
Free (SFE);
System.Soft_Links.Unlock_Task.all;
return null;
end;
-- Here if file is already open, set file for reading
else
if SIO.Mode (SFE.Stream.File) /= SIO.In_File then
SIO.Set_Mode (SFE.Stream.File, SIO.In_File);
SFI.Make_Unbuffered (To_AFCB_Ptr (SFE.Stream.File));
end if;
SIO.Set_Index (SFE.Stream.File, 1);
end if;
return SIO.Stream_Access (SFE.Stream);
exception
when others =>
System.Soft_Links.Unlock_Task.all;
raise;
end Shared_Var_ROpen;
-----------------------
-- Shared_Var_Unlock --
-----------------------
procedure Shared_Var_Unlock (Var : String) is
pragma Warnings (Off, Var);
begin
System.Soft_Links.Lock_Task.all;
Initialize;
Lock_Count := Lock_Count - 1;
if Lock_Count = 0 then
System.Global_Locks.Release_Lock (Global_Lock);
end if;
System.Soft_Links.Unlock_Task.all;
exception
when others =>
System.Soft_Links.Unlock_Task.all;
raise;
end Shared_Var_Unlock;
----------------------
-- Shared_Var_WOpen --
----------------------
function Shared_Var_WOpen (Var : String) return SIO.Stream_Access is
SFE : Shared_Var_File_Entry_Ptr;
use type Ada.Streams.Stream_IO.File_Mode;
begin
System.Soft_Links.Lock_Task.all;
SFE := Retrieve (Var);
if SFE = null then
declare
S : aliased constant String := Dir.all & Var;
begin
SFE := new Shared_Var_File_Entry;
SFE.Stream := new File_Stream_Type;
SIO.Open (SFE.Stream.File, SIO.Out_File, Name => S);
SFI.Make_Unbuffered (To_AFCB_Ptr (SFE.Stream.File));
exception
-- If we get an exception, it means that the file does not
-- exist, and in this case, we create the file.
when IOX.Name_Error =>
begin
SIO.Create (SFE.Stream.File, SIO.Out_File, Name => S);
exception
-- Error if we cannot create the file
when others =>
raise Program_Error with
"cannot create shared variable file for """ & S & '"';
end;
end;
-- Make new hash table entry for opened/created file. Note that
-- in both cases, the file is already in write mode at the start
-- of the file, ready to be written.
Enter_SFE (SFE, Var);
-- Here if file is already open, set file for writing
else
if SIO.Mode (SFE.Stream.File) /= SIO.Out_File then
SIO.Set_Mode (SFE.Stream.File, SIO.Out_File);
SFI.Make_Unbuffered (To_AFCB_Ptr (SFE.Stream.File));
end if;
SIO.Set_Index (SFE.Stream.File, 1);
end if;
return SIO.Stream_Access (SFE.Stream);
exception
when others =>
System.Soft_Links.Unlock_Task.all;
raise;
end Shared_Var_WOpen;
-----------
-- Write --
-----------
procedure Write
(Stream : in out File_Stream_Type;
Item : AS.Stream_Element_Array)
is
begin
SIO.Write (Stream.File, Item);
end Write;
end System.Shared_Storage;