🚀 go-pugleaf

Colin,

From my understanding, if you create a memory mapped file (or mutex or other 
kernel object) and you do not prefix it with anything, it is assumed to be 
"Local".  Therefore, it is local for the session that it is created in.  In 
vista this is more of a problem becuase all the services run in session 0. 
therefore if you create a MMF in session 0, with no prefixing, it is local 
to session 0 and NOT accessible / visiable outside that session.  Therefore, 
to get the system to function as you require, you just prefix it with 
"Global\\".  This should work in all cases, regardless of Vista or XP (the 
only exception being Windows 2K <).  I did not notice anothing in the 
article that suggested "at times".  I have a similar situation and it seems 
ot work in both Vista and XP.

Have you checked which part of your process is not working?

Is it the initial CreateFileMapping or the OpenFileMapping?

What does GetLastError() return?

What does ProcExplorer.exe show up as the file map name?

How are you controlling access to your MMF?

Mike C


"Colin B Maharaj" <noreply@myhost.com> wrote in message 
news:48637046$1@newsgroups.borland.com...
> Hi folks,
> I recently had to fix a bug where my memory mapped file
> that was running in my service application was not
> visible to my foreground application.
>
> To fix this I had to add Global to the name like this.....
>
> From: "MMAPFILE"
> To: "Global\\MMAPFILE"
>
> Had to do this to both my service and foreground application.
>
> Now in some cases it works fine, e.g. in my development environment
> it was not necessary for me to make these changes. It seems to
> be a namespace issue
>
> http://blogs.msdn.com/maartenb/archive/2008/05/07/memory-mapped-files-from-xp-to-vista.aspx
>
> In this article they articulate the problem - but with vista, however it 
> also applies, "at times", to XP services. The real problem being here is
> "at times".
>
>
> Question: (Finally)
> How do I know that the operating system will run my service and
> create memory mapped files within a separate namespace or not.
>
> thanks..
> 

Hi Mike, thanks for the reply,


Mike Collins wrote:
> Colin,
> 
> "Global\\".  This should work in all cases, regardless of Vista or XP (the 
> only exception being Windows 2K <).  I did not notice anothing in the 
> article that suggested "at times". 

The "at times" is what I have experienced in XP...
BTW: does Windows 2K < include Windows 2K or just NT/9x.

  I have a similar situation and it seems
> ot work in both Vista and XP.
> 
> Have you checked which part of your process is not working?
> 

The fact is that all objects are created without error.
However when you open the named object it simply says
file not found.

> Is it the initial CreateFileMapping or the OpenFileMapping?
> 
Open file mapping ...

> What does GetLastError() return?
> 
.... File Not found.


> What does ProcExplorer.exe show up as the file map name?
> 
Have to double check this....

> How are you controlling access to your MMF?
what do you mean by this? This is my code...

..........
// Code in Service

    bool Is9x = (Win32Platform == VER_PLATFORM_WIN32_WINDOWS);

    if (Is9x == false)//nt/2000/2003 server/xp pro/
    {
      //Beep(1000,20);
      SECURITY_DESCRIPTOR  sd;
      SECURITY_ATTRIBUTES  sa;
      InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
      SetSecurityDescriptorDacl(&sd, TRUE, NULL, FALSE);
      sa.nLength = sizeof(sa);
      sa.lpSecurityDescriptor = &sd;
      sa.bInheritHandle = TRUE;
      mmHandle = CreateFileMapping((HANDLE) 0xFFFFFFFF,
                  &sa, PAGE_READWRITE, 0, mmSize, __TEXT(mmName));
    }
    else
    {
      mmHandle = CreateFileMapping((HANDLE) 0xFFFFFFFF,
                  NULL, PAGE_READWRITE, 0, mmSize, __TEXT(mmName));
    }

...........

//Code in Front end client

    hFileMapT = OpenFileMapping(FILE_MAP_READ | FILE_MAP_WRITE,
       FALSE, __TEXT(mmName));




> 
> Mike C
> 
> 
> "Colin B Maharaj" <noreply@myhost.com> wrote in message 
> news:48637046$1@newsgroups.borland.com...
>> Hi folks,
>> I recently had to fix a bug where my memory mapped file
>> that was running in my service application was not
>> visible to my foreground application.
>>
>> To fix this I had to add Global to the name like this.....
>>
>> From: "MMAPFILE"
>> To: "Global\\MMAPFILE"
>>

Hay Colin, most of what i know is based on what remy has told me on this 
forum, but here goes...

> BTW: does Windows 2K < include Windows 2K or just NT/9x.

 - this includes Win2K - Global\\ is not valid on 2k

> The fact is that all objects are created without error.
> However when you open the named object it simply says
> file not found.

- Yep, the objects will be created without error - this does not mean that 
they are *visible* from outside the session that they are created in

> Open file mapping ...
> .... File Not found.

- this pretty much confirms what we're saying...

> What does ProcExplorer.exe show up as the file map name?
> Have to double check this....

- ProcExplorer is a god-send... Check it out from SysInternals...

>      mmHandle = CreateFileMapping((HANDLE) 0xFFFFFFFF,
>                  &sa, PAGE_READWRITE, 0, mmSize, __TEXT(mmName));

- does your mmName contain the "Global\\" prefix?  if not, include it, 
perminantly and see what you get - if works for me...


>    hFileMapT = OpenFileMapping(FILE_MAP_READ | FILE_MAP_WRITE,
>       FALSE, __TEXT(mmName));

- Like wise, make sure mmName here also contains the "Global\\" prefix.

Another point worth mentioning is that you should, depending on what you are 
doing with your MMF, protect access to it using a mutex, because there is 
the possibility that you *server Sis writting to the MMF, while yout 
*client* is trying to access it...

HTH

Mike C