c# - 结构数组指针的问题

Question

我想通过使用 ntdll 中的 NtQuerySystemInformation 获取有关每个处理器性能的信息。现在我遇到的问题是它只运行了所有 5 次尝试然后返回。

NtQuerySystemInformation 返回一个 NtStatus，它始终是 InfoLengthMismatch，这通常意味着我必须使我的缓冲区更大。如果我只使用一个处理器(无数组)和 0x10000 的缓冲区大小来尝试它，它工作得很好，它在第一次尝试时给了我 InfoLengthMismatch，但第二次尝试总是有效。

我尝试将缓冲区增加 100 倍，也尝试增加 1000 倍，但没有任何效果。

private _SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION[] GetPerformanceInfo()
    {
        try
        {
            //Getting count of processors
            SYSTEM_INFO sysInfo = new SYSTEM_INFO();
            GetSystemInfo(out sysInfo);
            int processors = (int)sysInfo.numberOfProcessors;

            int tries = 0;

            while (true)
            {

                //buffer size
                uint infoLength = (uint)(Marshal.SizeOf(typeof(_SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION)) * processors);

                //buffer
                IntPtr infoPtr = Marshal.AllocHGlobal((int)infoLength);

                //Problem: result is always InfoLengthMismatch
                NtStatus result = NtQuerySystemInformation(SYSTEM_INFORMATION_CLASS.SystemProcessorPerformanceInformation, infoPtr, infoLength, out infoLength);

                //if success, get the array and return it
                if (result == NtStatus.Success)
                {
                    int szStruct = Marshal.SizeOf(typeof(_SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION));
                    _SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION[] localStructs = new _SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION[processors];

                    for (uint i = 0; i < processors; i++)
                        localStructs[i] = (_SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION)Marshal.PtrToStructure(new IntPtr(infoPtr.ToInt64() + (szStruct * processors)), typeof(_SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION));

                    return localStructs;
                }

                //free ptr when fail
                Marshal.FreeHGlobal(infoPtr);

                if (++tries > 5)
                    return null;

                //set ptr again, new try
                infoPtr = Marshal.AllocHGlobal((int)infoLength);

            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Source + ": " + e.Message.ToString());
            return null;
        }
    }

}

//struct of a large int
[StructLayout(LayoutKind.Explicit, Size = 8)]
public struct LARGE_INTEGER
{
    [FieldOffset(0)] public Int64 QuadPart;
    [FieldOffset(0)] public UInt32 LowPart;
    [FieldOffset(4)] public Int32 HighPart;
}

//struct
public struct _SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION
{
    public LARGE_INTEGER IdleTime;
    public LARGE_INTEGER KernelTime;
    public LARGE_INTEGER UserTime;
    public LARGE_INTEGER Reserved1;
    public ulong Reserved2;
}

编辑:这一行有误:

uint infoLength = (uint)(Marshal.SizeOf(typeof(_SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION)) * processors);

通常如果大小错误，它会将正确的大小输出到 infoLength var，但在这种情况下，我每次都在循环开始时设置它。

Answer 1

我注意到了一些事情。首先，您分配了两次内存，并且只释放了一次:

//buffer
IntPtr infoPtr = Marshal.AllocHGlobal((int)infoLength);

//...

//free ptr when fail
Marshal.FreeHGlobal(infoPtr);

//...

//set ptr again, new try
infoPtr = Marshal.AllocHGlobal((int)infoLength);

其次，当NtQuerySystemInformation 返回错误时，它会将可选的输出参数设置为所需的大小。与我看到的不同，您创建的缓冲区大小是 8 * 5 * processors。或 40 * 处理器。

您可以通过在调用前后输出 infoLength 来确认这一点以及所需的适当大小。

// Should be 40 * processors
Console.WriteLine((int)infoLength);

//Problem: result is always InfoLengthMismatch
NtStatus result = NtQuerySystemInformation(SYSTEM_INFORMATION_CLASS.SystemProcessorPerformanceInformation, 
                      infoPtr, infoLength, out infoLength);

// Will be bigger than 40 * processors
Console.WriteLine((int)infoLength);