Question

随着C＃7.2中的Memory，Span和ArraySegment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，该对象驻留在堆中。 / p>

后一项要求排除了Span，该要求基本上实现了我想要的功能：例如

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

是否可以对ArraySegment或Memory做同样的事情？他们的构造函数只接受byte[]，也许有某种方法可以欺骗C＃传递byte*而不是byte[]？

Answer 1

对于Memory<T>是，但是您需要创建自己的MemoryManager<T>。不用担心-这并不像听起来那样可怕-here's one I wrote earlier...：

/// <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;

和memory可以存储在堆中。

但是，为了最大程度地减少分配，您可能想要创建一个覆盖整个区域的单个 UnmanagedMemoryManager<byte>-仅使用一次-然后使用{{1}代表整个区域的.Slice(...)上的}。这样，您将拥有一个对象和许多切片（切片是结构，而不是对象）。

请注意，此实现假定您要控制其他地方的内存寿命-这里的.Memory 不会尝试通过Dispose()释放内存。

C＃使用Memory <t>或ArraySegment <t>访问非托管数组吗？

1 个答案: