WinXP Compatibility for PdhUtil#PdhLookupPerfNameByIndex

[dbwiddis]

See discussion on JNA mailing list. WinXP requires non-null buffer and non-zero size for PdhLookupPerfNameByIndex. But we can't always set a too-small buffer for Vista+ as the returned size is not reliable without the null.

This method should bypass the error conditional (more quickly over time with branch prediction) on modern OS's but provide XP compatibility with a third call if required.

Other ways to address this:

• Do a version check for Vista+ (see Add Windows Version Helper functions #1050) and save that boolean result, and use that for the conditional
• Always set a big-enough buffer (PDH_MAX_COUNTER_NAME(1024) * Native.WCHAR_SIZE) on the first call.

[matthiasblaesing]

Thank you - looks sane.

[dbwiddis]

Ugh, missed asking you to hold on this by a few hours. Doing more testing, discovered it doesn't quite fix the problem: the XP call that returns insufficient buffer isn't guaranteed to provide the new size... the docs give an either/or.

The function sets pcchNameBufferSize to either the required size or the size of the buffer that was used.

I need to wrap the XP fallback attempt in a loop that increases the buffer size until success.