[Boost-users] [Interprocess] Different shared memory locations in Windows

Subject: [Boost-users] [Interprocess] Different shared memory locations in Windows
From: Aaron_Wright_at_[hidden]
Date: 2012-09-13 20:02:42

I'm attempting to share memory between two services on a Windows Server 
2008 Core box. One service is postgres running as a user created just for 
that purpose, and the other service is my application running as the Local 
System user.

The issue I'm seeing is that it seems that the two services do not agree 
on the location of the shared memory files. The postgres service is 
looking at "C:\Users\<user>\AppData\Local\Temp\boost_interprocess", while 
my application is looking at "C:\Windows\TEMP". Diving into the code I 
found that it first tries to use the value of a registry key, 
"HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Shell 
Folders\Common AppData", however this key doesn't exist in Windows Server 
2008 R2 Core, presumably because there is no explorer.exe running on the 
box, and thus, no shell folders under it. When that fails, the code 
attempts to use the  TMP environment variable, however that is dependent 
upon the environment that the user has setup, so the TMP variable is not 
guaranteed to be the same across users. Indeed in my case the TMP variable 
for the Local System user was "C:\Windows\TEMP", while the TMP variable 
for the other user was in its user folder.

I'm not sure what the correct answer here is, but I have some ideas:

-- The "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\User Shell 
Folders\Common AppData" registry key seems to exist for Windows XP, 
Windows Server 2008 R2 Core, and Windows 7. And according to TechNet, "The 
entries that appear in user User Shell Folders take precedence over those 
in Shell Folders." So maybe that registry key should be used instead.

-- Use the ALLUSERESPROFILE variable, which is "C:\Documents and 
Settings\All Users" on Windows XP, and "C:\ProgramData" on Windows Server 
2008 R2 Core and Windows 7. The TMP variable seems to be different for 
every user.

-- Provide a way to tell the library what directory to use. (This doesn't 
exist does it?) Or hint at what library to use.

-- Can/Should the code assert when the folder chosen contains a user name. 
Might be impracticable, but sure helpful.

---
Aaron Wright