c# - 为什么分配的内存比预期的多？

Question

我正在使用 BenchmarkDotNet 及其 MemoryDiagnoser 功能。

考虑以下基准:

[Benchmark]
public void Dummy()
{
   var buffer = new byte[1];
}

我希望它恰好分配 1 个字节。

但是基准测试结果显示总共分配了 32 个字节。怎么来的？我觉得这很有误导性。

| Method |     Mean |     Error |    StdDev |   Median | Ratio | Rank |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|------- |---------:|----------:|----------:|---------:|------:|-----:|-------:|------:|------:|----------:|
|  Dummy | 4.486 ns | 0.1762 ns | 0.5196 ns | 4.650 ns |  1.00 |    1 | 0.0038 |     - |     - |      32 B |

                                                                                      why not 1 byte? ^^^^

Answer 1

我是 MemoryDiagnoser 的作者，我已经描述了如何阅读我的博客的结果:https://adamsitnik.com/the-new-Memory-Diagnoser/#how-to-read-the-results

CLR does some aligning. If you try to allocate new byte[1] array, it will allocate byte[8] array.

We need extra space for object header, method table pointer and length of the array. The overhead is 3x Pointer Size. 8 + 3x4 = 20 for 32bit and 8 + 3x8 = 32 for 64bit.