MemStatus

Description

There's more to this one than you might at first suspect. Yeah, the basic premise is very straight-forward. This sample provides you a means to determine the amount of physical memory installed in the machine, the total size of the machine's swap file, and the size of the virtual address space the operating system has provided you with. For each of these metrics, you may obtain both the total and available amounts. All this information is returned by the drop-in ready CMemoryStatus class that's included with this download.

I've written a little sample utility that exercises CMemoryStatus by monitoring (on a timer) how much of each of the memory amounts mentioned above are available. It then offers you the ability to fully utilize your process's entire address space. When you press the "Start" button in this test app, it begins allocating chunks of memory 25 megabytes in a gulp until it's all gone. Note the changes below in the Available memory entries on the "before" (right) and "after" (left) forms below:

That might be semi-interesting in and of itself, in many circumstances. Where it gets really interesting is if you happen to be running on a system that supports large address spaces. By default, this is any 64-bit operating system, or 32-bit operating systems (Win2k+) where the boot.ini file has been tweaked with a /3G switch. Ready for a shock? Check out how this same utility runs on Windows 7 x64:

By toggling a single bit in your application's PE header, you can now allocate nearly 4GB of data! At least when you're running on an x64 system. More info is available in my recent article in Visual Studio Magazine Online (see below). But here's the gist of it:
D:\Code\Samples\MemStatus>editbin /largeaddressaware memmax.exe
Microsoft (R) COFF Binary File Editor Version 6.00.8447
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.

D:\Code\Samples\MemStatus>
Pretty cool? So far, yeah, I think so! More testing required to be really sure. Let me know if you run into troubles with this.

CMemoryStatus Enumerations
Public Enum MemoryTypes
   memPhysical = 0
   memPagefile = 1
   memVirtual = 2
End Enum
CMemoryStatus Properties

Available Returns the number of bytes available given one of the three MemoryTypes enum values.

Change Returns the change in the number of bytes available, given one of the three MemoryTypes enum values, since the last time the Refresh method was called.

Load Returns the approximate percentage of physical memory that is in use.

Total Returns the total number of bytes given one of the three MemoryTypes enum values.

CMemoryStatus Methods

FormatBytes Returns a nicely formatted string, representing the number passed, in Bytes, KB, MB, GB, or TB, as appropriate.

Refresh Calls GlobalMemoryStatusEx and refreshes all the cached statistics provided by the class.

To use CMemoryStatus, just drop it into your project, create a new instance, and start querying it:
Public Sub Main()
   Dim msg As String
   Dim ms As CMemoryStatus
   Set ms = New CMemoryStatus
   msg = msg & "TotalPhysical = " & ms.FormatBytes(ms.Total(memPhysical), True) & vbCrLf
   msg = msg & "AvailPhysical = " & ms.FormatBytes(ms.Available(memPhysical), True) & vbCrLf
   msg = msg & "TotalPageFile = " & ms.FormatBytes(ms.Total(memPagefile), True) & vbCrLf
   msg = msg & "AvailPageFile = " & ms.FormatBytes(ms.Available(memPagefile), True) & vbCrLf
   ' editbin /largeaddressaware memstatus.exe
   msg = msg & "TotalVirtual = " & ms.FormatBytes(ms.Total(memVirtual), True) & vbCrLf
   msg = msg & "AvailVirtual = " & ms.FormatBytes(ms.Available(memVirtual), True) & vbCrLf
   Debug.Print msg
   Clipboard.Clear
   Clipboard.SetText msg
   MsgBox msg, vbInformation, "Memory Status"
End Sub

Published

This sample, or the one from which it originally derived, was published (or at least peripherally mentioned) in the following article(s):

Easing the Data Cramp, Classic VB Corner, VSM Online, March 2010

APIs Usage

This sample uses the following API calls:

Module Library Function

CMemoryStatus.cls kernel32 GlobalMemoryStatusEx

MMemMax.bas comctl32 InitCommonControls

Don't see what you're looking for? Here's a complete API cross-reference.

Module	Library	Function
CMemoryStatus.cls	kernel32	GlobalMemoryStatusEx
MMemMax.bas	comctl32	InitCommonControls

Download

Please, enjoy and learn from this sample. Include its code within your own projects, if you wish. But, in order to insure only the most recent code is available to all, I ask that you don't share the sample by any form of mass distribution.
Download MemStatus.zip, 22Kb, Last Updated: Friday, February 19, 2010

Available	Returns the number of bytes available given one of the three MemoryTypes enum values.
Change	Returns the change in the number of bytes available, given one of the three MemoryTypes enum values, since the last time the Refresh method was called.
Load	Returns the approximate percentage of physical memory that is in use.
Total	Returns the total number of bytes given one of the three MemoryTypes enum values.

FormatBytes	Returns a nicely formatted string, representing the number passed, in Bytes, KB, MB, GB, or TB, as appropriate.
Refresh	Calls GlobalMemoryStatusEx and refreshes all the cached statistics provided by the class.