内存泄漏？传递 IEnumerable时数组到非托管函数作为 byte** 参数

Question

这是分配和释放传递给非托管 dll 的托管数据句柄的正确方法吗？

有一个带有导出函数的非托管 dll，

void Function(byte** ppData, int N);

我需要将其传递给 IEnumerableafids

var handles = afids.Select(afid => GCHandle.Alloc(afid, GCHandleType.Pinned));
var ptrs = handles.Select(h => h.AddrOfPinnedObject());
IntPtr[] afidPtrs = ptrs.ToArray();
uint N = (uint)afidPtrs.Length;

Function(afidPtrs, N);

handles.ToList().ForEach(h => h.Free());

我得到托管内存泄漏，并在立即窗口中获取 sos.dll 给出了 gcroot

DOMAIN(00275030):HANDLE(Pinned):3ea2c0:Root:  17a8d190(System.Byte[])

函数定义是：

[DllImport("My.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
static extern unsafe internal int Function(IntPtr[] ppData, int N);

控制台应用程序的错误代码片段：

static void Main(string[] args)
{
    while (!Console.KeyAvailable)
    {
        IEnumerable<byte[]> data = CreateEnumeration(100);
        PinEntries(data);
        Thread.Sleep(900);
        Console.Write(String.Format("gc mem: {0}\r", GC.GetTotalMemory(true)));
    }
}

static IEnumerable<byte[]> CreateEnumeration(int size)
{
    Random random = new Random();
    IList<byte[]> data = new List<byte[]>();
    for (int i = 0; i < size; i++)
    {
        byte[] vector = new byte[12345];
        random.NextBytes(vector);
        data.Add(vector);
    }
    return data;
}

static void PinEntries(IEnumerable<byte[]> data)
{
    var handles = data.Select(d => GCHandle.Alloc(d, GCHandleType.Pinned));
    var ptrs = handles.Select(h => h.AddrOfPinnedObject());
    IntPtr[] dataPtrs = ptrs.ToArray();
    Thread.Sleep(100); // unmanaged function call taking byte** data
    handles.ToList().ForEach(h => h.Free());
}

控制台应用程序的正确代码片段：

static void PinEntries(IEnumerable<byte[]> data)
{
    IEnumerable<GCHandle> handles = CreateHandles(data);
    IntPtr[] ptrs = GetAddrOfPinnedObjects(handles);
    Thread.Sleep(100); // unmanaged function call taking byte** data
    FreeHandles(handles);
}

static IEnumerable<GCHandle> CreateHandles(IEnumerable<byte[]> data)
{
    IList<GCHandle> handles = new List<GCHandle>();
    foreach (byte[] vector in data)
    {
            GCHandle handle = GCHandle.Alloc(vector, GCHandleType.Pinned);
            handles.Add(handle);
    }
    return handles;
}

static IntPtr[] GetAddrOfPinnedObjects(IEnumerable<GCHandle> handles)
{
    IntPtr[] ptrs = new IntPtr[handles.Count()];
    for (int i = 0; i < ptrs.Length; i++)
            ptrs[i] = handles.ElementAt(i).AddrOfPinnedObject();
    return ptrs;
}

static void FreeHandles(IEnumerable<GCHandle> handles)
{
    foreach (GCHandle handle in handles)
            handle.Free();
}

Answer 1

static void PinEntries(IEnumerable<byte[]> data)
{
    var handles = data.Select(d => GCHandle.Alloc(d, GCHandleType.Pinned));
    var ptrs = handles.Select(h => h.AddrOfPinnedObject());
    IntPtr[] dataPtrs = ptrs.ToArray();
    Thread.Sleep(100); // unmanaged function call taking byte** data
    handles.ToList().ForEach(h => h.Free());
}

您陷入了 Linq 陷阱，它的枚举器的行为不像集合。句柄被分配两次，第一次是当您使用ptrs.ToArray()时，再次是当您使用handles.ToList()时。明显的副作用是第一组句柄不会被释放。修复：

        var handles = data.Select(d => GCHandle.Alloc(d, GCHandleType.Pinned)).ToList();
        var ptrs = handles.Select(h => h.AddrOfPinnedObject());
        IntPtr[] dataPtrs = ptrs.ToArray();
        handles.ForEach(h => h.Free());

注意添加的 ToList() 以强制将枚举放入集合中。