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随着Memory,Span和ArraySegmentC# 7.2 的引入，我想知道是否可以将非托管数组表示为可枚举的对象，它存在于堆上。

后一个要求排除了Span，它基本上完全实现了我想要的：例如

unsafe { bytes = new Span<byte>((byte*)ptr + (index * Width), Width);

是否可以用ArraySegmentor做同样的事情Memory？他们的构造函数只接受byte[]，也许有一些方法可以欺骗 C# 传递 abyte*而不是byte[]?

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1 回答 1

24

是的Memory<T>，但您需要创建自己的MemoryManager<T>. 别担心 - 这并不像听起来那么可怕 - 这是我之前写的一个......：

/// <summary>
/// A MemoryManager over a raw pointer
/// </summary>
/// <remarks>The pointer is assumed to be fully unmanaged, or externally pinned - no attempt will be made to pin this data</remarks>
public sealed unsafe class UnmanagedMemoryManager<T> : MemoryManager<T>
    where T : unmanaged
{
    private readonly T* _pointer;
    private readonly int _length;

    /// <summary>
    /// Create a new UnmanagedMemoryManager instance at the given pointer and size
    /// </summary>
    /// <remarks>It is assumed that the span provided is already unmanaged or externally pinned</remarks>
    public UnmanagedMemoryManager(Span<T> span)
    {
        fixed (T* ptr = &MemoryMarshal.GetReference(span))
        {
            _pointer = ptr;
            _length = span.Length;
        }
    }
    /// <summary>
    /// Create a new UnmanagedMemoryManager instance at the given pointer and size
    /// </summary>
    public UnmanagedMemoryManager(T* pointer, int length)
    {
        if (length < 0) throw new ArgumentOutOfRangeException(nameof(length));
        _pointer = pointer;
        _length = length;
    }
    /// <summary>
    /// Obtains a span that represents the region
    /// </summary>
    public override Span<T> GetSpan() => new Span<T>(_pointer, _length);

    /// <summary>
    /// Provides access to a pointer that represents the data (note: no actual pin occurs)
    /// </summary>
    public override MemoryHandle Pin(int elementIndex = 0)
    {
        if (elementIndex < 0 || elementIndex >= _length)
            throw new ArgumentOutOfRangeException(nameof(elementIndex));
        return new MemoryHandle(_pointer + elementIndex);
    }
    /// <summary>
    /// Has no effect
    /// </summary>
    public override void Unpin() { }

    /// <summary>
    /// Releases all resources associated with this object
    /// </summary>
    protected override void Dispose(bool disposing) { }
}

现在您可以使用：

var mgr = new UnmanagedMemoryManager((byte*)ptr + (index * Width), Width);
Memory<byte> memory = mgr.Memory;

并且memory可以存储在堆上。

但是，为了最小化分配，您可能希望创建一个覆盖整个区域的单个 - 仅一次 - 然后在代表整个区域的 上使用。这样你就有了一个对象和很多切片（切片是结构，而不是对象）。UnmanagedMemoryManager<byte>.Slice(...).Memory

请注意，此实现假定您将在其他地方控制内存的生命周期 -Dispose()这里不会尝试通过Marshal等释放内存。

于 2018-09-05T18:48:46.223 回答