Question

I’m attempting to get the allocation granularity size using GetSystemInfo() from a C# 3.5 windows service application on Windows 7. However the SYSTEM_INFO struct always has 0 in dwAllocationGranularity when it is returned from the call (other fields have data filled in as expected)

The SYSTEM_INFO struct looks like this with PROCESSOR_ARCHITECTURE and PROCESSOR_TYPE enums omitted for brevity:

public struct SYSTEM_INFO
{
    public PROCESSOR_ARCHITECTURE wProcessorArchitecture;
    public ushort wReserved;
    public uint dwPageSize;
    public int lpMinimumApplicationAddress;
    public int lpMaximumApplicationAddress;
    public uint dwActiveProcessorMask;
    public uint dwNumberOfProcessors;
    public PROCESSOR_TYPE dwProcessorType;
    public uint dwAllocationGranularity;
    public ushort wProcessorLevel;
    public ushort wProcessorRevision;
}

The extern call to GetSystemInfo is this:

[DllImport("kernel32")]
public static extern void GetSystemInfo(ref SYSTEM_INFO SystemInfo); 

The calling code is like this:

SYSTEM_INFO sysInfo = new SYSTEM_INFO();
GetSystemInfo(ref sysInfo);

The Output SYS_INFO struct after running code is:

dwActiveProcessorMask        4294901759
dwAllocationGranularity      0
dwNumberOfProcessors         2047
dwPageSize                   4096
dwProcessorType              15
lpMaximumApplicationAddress  0
lpMinimumApplicationAddress  65536
wProcessorArchitecture       9
wProcessorLevel              4
wProcessorRevision           0
wReserved                    0

Any ideas what I’m missing or suggestions on other ways to get this info (I don’t want to hard code to 64Kb JIC it is changed at some point)? Thanks.

Answer 1

You also don’t have 2047 processors 🙂 The declaration is wrong, it will fail in 64-bit mode. lpMin/MaxApplicationAddress and dwActiveProcessorMask are IntPtr.