我怎样才能快速阅读：在.NET内存映射文件的字节？ [英] How can I quickly read bytes from a memory mapped file in .NET?

问题描述

在某些情况下， MemoryMappedViewAccessor ​​类只是不削减它有效地读取字节;我们得到的最好的是通用的 ReadArray<字节方式> 它所有结构的路线，包括当你只是需要字节数不必要的步骤

In some situations the MemoryMappedViewAccessor class just doesn't cut it for reading bytes efficiently; the best we get is the generic ReadArray<byte> which it the route for all structs and involves several unnecessary steps when you just need bytes.

这是可以使用 MemoryMappedViewStream ，但由于它是基于一个流您需要求到正确的位置，然后再读取操作本身有许多更多不必要的步骤

It's possible to use a MemoryMappedViewStream, but because it's based on a Stream you need to seek to the correct position first, and then the read operation itself has many more unnecessary steps.

是否有一个快速，高性能的方式来从读取的字节的阵列内存映射文件在.NET中，因为它应该只是地址空间的特定区域进行读操作？

Is there a quick, high-performance way to read an array of bytes from a memory-mapped file in .NET, given that it should just be a particular area of the address space to read from?

推荐答案

此解决方案要求不安全的代码（编译 /不安全开关），而是抓住一个指向直接内存;那么 Marshal.Copy 可以使用。这是多少，比由.NET框架提供的方法要快得多。

This solution requires unsafe code (compile with /unsafe switch), but grabs a pointer to the memory directly; then Marshal.Copy can be used. This is much, much faster than the methods provided by the .NET framework.

    // assumes part of a class where _view is a MemoryMappedViewAccessor object

    public unsafe byte[] ReadBytes(int offset, int num)
    {
        byte[] arr = new byte[num];
        byte *ptr = (byte*)0;
        this._view.SafeMemoryMappedViewHandle.AcquirePointer(ref ptr);
        Marshal.Copy(IntPtr.Add(new IntPtr(ptr), offset), arr, 0, num);
        this._view.SafeMemoryMappedViewHandle.ReleasePointer();
        return arr;
    }

    public unsafe void WriteBytes(int offset, byte[] data)
    {
        byte* ptr = (byte*)0;
        this._view.SafeMemoryMappedViewHandle.AcquirePointer(ref ptr);
        Marshal.Copy(data, 0, IntPtr.Add(new IntPtr(ptr), offset), data.Length);
        this._view.SafeMemoryMappedViewHandle.ReleasePointer();
    }

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