Using ALIAS as Shared Memory

[Joe Caverly]

There are many ways to share memory with TCC 64-bit and a 32-bit application.

Here's a method that I use.

In the source code below,
and the notes that follow,
I have a few issues,
but they have not caused any problems,
or crashes,
when using this method.

@echo off
iff %_shralias ne 1 then
  echo Shralias must be in memory.
  quit
endiff

iff %_admin ne 1 then
  echo Admin level is required to run %_batchname
  quit
endiff

unalias smjlcav*
memory | ffind /kvme"global|free"
test.exe
echo Contents of the smjlcav alias...
alias smjlcav
echo Storing the contents of smjlcav to an environment variable...
set smjlcav=%@alias[smjlcav]
echo smjlcav = : %smjlcav
unalias smjlcav*

I use 32-bit Visual Basic 6.0,
32-bit Visual FoxPro 9.0
and 32-bit PowerBASIC

It should be easy for C++ people to re-create this.

I chose PowerBASIC for this example,
as it is lower-level than VB6 or VFP9

PowerBASIC Code (compiled to test.exe)

#COMPILE EXE
#DIM ALL
#INCLUDE "Win32api.inc"

FUNCTION PBMAIN () AS LONG
  LOCAL hMap AS LONG, MapName AS ASCIIZ * 64, lRet AS LONG
  LOCAL kount AS LONG, AliasString AS STRING, mmsize AS LONG, theEof AS LONG

  '\Sessions\1\BaseNamedObjects\SharememUAliasjlcav
  MapName = "SharememUAliasjlcav" '<-- Change this to your MapName

  lRet = OpenFileMapping _
         (%FILE_MAP_ALL_ACCESS,_ ' access mode
         BYVAL %NULL, _ ' inherit flag
         MapName) ' pointer to name of file-mapping object

  IF lRet THEN
    hMap = MapViewOfFile _
           (lRet,_ ' file-mapping object to map into address space
           %FILE_MAP_ALL_ACCESS,_ ' access mode
           0,_ ' high-order 32 bits of file offset
           0,_ ' low-order 32 bits of file offset
           0) ' number of bytes to map

    ' The TCC Memory command returns...
    ' 262,144 characters total global alias
    ' 262144 * 2 = 524288
    ' Would like to determine mmfsize
    '  instead of hard-coding size.
    mmsize = 524288

    AliasString = ACODE$(PEEK$(hMap,mmsize))

    theEof = INSTR(AliasString,CHR$(0) + CHR$(0))
    STDOUT "Length of Shared Memory in use: ";
    STDOUT STR$(theEOF)
    ' In my case,
    '   this returns 22,481
    '
    ' TCC Memory command returns...
    ' 262,144 characters total global alias
    ' 239,662 characters free
    ' -------
    ' 22,482 <- 1 byte difference.

    FOR kount = 1 TO mmsize
      IF MID$(AliasString, Kount, 1) = CHR$(0) AND MID$(AliasString, Kount + 1, 1) = CHR$(0) THEN
        MID$(AliasString,kount) = CHR$(0) + "smjlcav=This is shared memory" + CHR$(0)
        POKE$ hMap,UCODE$(AliasString)
        EXIT FOR
      END IF
    NEXT kount
  ELSE
    STDOUT "Cannot open file mapping" + CHR$(10) + CHR$(13) + "Filemap must exist!"
  END IF
  UnmapViewOfFile BYVAL lRet
  CloseHandle hMap
END FUNCTION

Notes:
Running TEST.EXE repeatedly will create several SMJLCAV aliases!

E:\...\Alias>test.exe
Length of Shared Memory in use:  22481

E:\...\Alias>test.exe
Length of Shared Memory in use:  22511

E:\...\Alias>test.exe
Length of Shared Memory in use:  22541

E:\...\Alias>alias smjlc*
smjlcav=This is shared memory
smjlcav=This is shared memory
smjlcav=This is shared memory

To remove all of the SMJLCAV aliases...

E:\...\Alias>unalias smjlcav*

E:\...\Alias>alias smjlc*
TCC: Not an alias "smjlc*"

I have used Alias as Shared Memory.
It may also be possible to use Function and History as Shared Memory.

I used handle.exe from www.sysinternals.com to get the name of Alias MMF
You could also use Process Explorer from the same site.

tcc.exe pid: 6088 DESKTOP-LFBF7P3\jlcav
  37C: Section       \Sessions\1\BaseNamedObjects\SharememUAliasjlcav
  3E0: Section       \Sessions\1\BaseNamedObjects\SharememUFunctionjlcav
  3E4: Section       \Sessions\1\BaseNamedObjects\SharememUHistoryjlcav
  3E8: Section       \Sessions\1\BaseNamedObjects\SharememUDirHistoryjlcav

I have been using this method for several years,
and am posting it in the event others might find it useful.

Joe

     _x64: 1
   _admin: 1
_elevated: 1

TCC  31.01.22 x64   Windows 10 [Version 10.0.19045.4046]
BuildNumber  Caption                   CSDVersion  OSArchitecture  Version
19045        Microsoft Windows 10 Pro              64-bit          10.0.19045