First call to Windows Performance Counters (PDH) sometimes fails - c++

Question

I'm having a problem where sometimes my code will function correctly, but other times it will fail.
This is the first bit of PDH related code that I run:
const std::wstring pidWildcardPath = L"\\Process(*)\\ID Process";
DWORD bufferSize = 0;
LPTSTR paths = NULL;
PDH_STATUS status = PdhExpandCounterPath(
pidWildcardPath.c_str(),
paths,
&bufferSize);
checkPDHStatus(status, PDH_MORE_DATA, L"Expected request for more data.");
The result of the PdhExpandCounterPath function call is 0x800007D0 (PDH_CSTATUS_NO_MACHINE). The checkPDHStatus function is a simple function that I wrote that asserts that the status is equal to the second parameter. In this case, I expect the result to be PDH_MORE_DATA because paths is NULL and bufferSize is 0. The goal of this call is to determine the size of the buffer I must allocate to store all of the results for a subsequent call to PdhExpandCounterPath. This is described in the PDH documentation under the Remarks section.
The list of PDH error codes describes PDH_MORE_DATA as "Unable to connect to the specified computer, or the computer is offline." As you can see by the performance counter path in the code above, I am not even trying to connect to a different computer than my own.
It is interesting the way that this code fails. Sometimes it works fine and then other times, it will fail on multiple back-to-back executions of my application. I have #include <pdh.h> in my header file and I have a section in my property sheet for this DLL that looks like this:
<Tool
Name="VCLinkerTool"
AdditionalDependencies="pdh.lib"
/>
I'm not sure if it matters, but this program is built by Visual Studio 2005 and run on Windows XP. Am I doing something incorrectly?
I'm a co-worker of Dave's and have discovered the following during my investigation:
the code above runs fine when run from a logged-in interactive session
the code runs fine when initiated as a Scheduled Task AND the user is logged in at the time the scheduled task is fired off
the code FAILS only when run as a Scheduled Task AND the user is NOT logged in at the time the task starts
the code continues to fail if the user logs in after the failing task has started but while it is still running (because it is looping "endlessly" until it gets a PDH_MORE_DATA status back).
In the failing instances, the following environment variables have not been established/set for the program: APPDATA, HOMEDRIVE and HOMEPATH ... I don't think this is a problem. However, the failing program also lacks the SeCreateGlobalPrivilege from its token; the passing programs all have this privilege in the token and PERFMON shows it as "Default Enabled". The other difference is that failing program has the NT_AUTH\BATCH user group in the token, while the passing program has NT_AUTH\INTERACTIVE instead ... all other user groups and privileges are the same for both cases. I think the global privilege is coming from the interactive login, but don't know if it has any bearing on PDH operation.
I cannot find anything in the Performance Counter/PDH documentation that talks about needing any special permissions or privileges for this functionality to succeed. Is the global privilege required to use Performance Counters ?
Or is there some other context/environment difference between running Scheduled Tasks (as a specific user) when that user is/isn't logged in at the time the task starts, that would account for the PDH call succeeding/failing respectively ?

Answer 1

Try this format, indicating the local computer:
const std::wstring pidWildcardPath = L"\\.\Process(*)\ID Process";