C#+无unsafe的非托管大数组示例详解(large unmanaged array in c# without ‘unsafe’ keyword)

C#申请一个大数组(Use a large array in C#)

在C#里，有时候我需要能够申请一个很大的数组、使用之、然后立即释放其占用的内存。

Sometimes I need to allocate a large array, use it and then release its memory space immediately.

由于在C#里提供的 int[] array = new int[1000000]; 这样的数组，其内存释放很难由程序员完全控制，在申请一个大数组后，程序可能会变得很慢。

If I use something like  int[] array = new int[1000000]; , it will be difficult to release its memory space by programmer and the app probably runs slower and slower.

特别是在C#+OpenGL编程中，我在使用VAO/VBO时十分需要设计一个非托管的数组，比如在glBufferData时我希望可以使用下面的glBufferData：

Specially in C#+OpenGL routines when I'm using VAO/VBO, I need an unmanaged array for glBufferData:

/// <summary>
 /// 设置当前VBO的数据。
 /// </summary>
 /// <param name="target"></param>
 /// <param name="data"></param>
 /// <param name="usage"></param>
 public static void glBufferData(uint target, UnmanagedArrayBase data, uint usage)
 {
 GetDelegateFor<glBufferData>()((uint)target,
 data.ByteLength, // 使用非托管数组
 data.Header, // 使用非托管数组
 (uint)usage);
 }
 // ...
 // glBufferData的声明
 private delegate void glBufferData(uint target, int size, IntPtr data, uint usage);

而在指定VBO的数据时，可能是float、vec3等等类型：

And the content in VBO can be float, vec3 and any other structs.

/// <summary>
 /// 金字塔的posotion array.
 /// </summary>
 static vec3[] positions = new vec3[]
 {
 new vec3(0.0f, 1.0f, 0.0f),
 new vec3(-1.0f, -1.0f, 1.0f),
 // ...
 new vec3(-1.0f, -1.0f, 1.0f),
 };
// Create a vertex buffer for the vertex data.
 {
 uint[] ids = new uint[1];
 GL.GenBuffers(1, ids);
 GL.BindBuffer(GL.GL_ARRAY_BUFFER, ids[0]);
 // 使用vec3作为泛型的非托管数组的参数
 UnmanagedArray<vec3> positionArray = new UnmanagedArray<vec3>(positions.Length);
 for (int i = 0; i < positions.Length; i++)
 {
  // 使用this[i]这样的索引方式来读写非托管数组的元素
  positionArray[i] = positions[i];
 }
 GL.BufferData(BufferDataTarget.ArrayBuffer, positionArray, BufferDataUsage.StaticDraw);
 GL.VertexAttribPointer(positionLocation, 3, GL.GL_FLOAT, false, 0, IntPtr.Zero);
 GL.EnableVertexAttribArray(positionLocation);
 }

UnmanagedArray<T>

所以我设计了这样一个非托管的数组类型：无unsafe，可接收任何struct类型作为泛型参数，可随时释放内存。

So I designed this UnmangedArray<T> : no 'unsafe' keyword, takes any struct as generic parameter, can be released anytime you want.

1 /// <summary>
 2 /// 元素类型为sbyte, byte, char, short, ushort, int, uint, long, ulong, float, double, decimal, bool或其它struct的非托管数组。
 3 /// <para>不能使用enum类型作为T。</para>
 4 /// </summary>
 5 /// <typeparam name="T">sbyte, byte, char, short, ushort, int, uint, long, ulong, float, double, decimal, bool或其它struct, 不能使用enum类型作为T。</typeparam>
 6 public class UnmanagedArray<T> : UnmanagedArrayBase where T : struct
 7 {
 8
 9 /// <summary>
 10 ///元素类型为sbyte, byte, char, short, ushort, int, uint, long, ulong, float, double, decimal, bool或其它struct的非托管数组。
 11 /// </summary>
 12 /// <param name="count"></param>
 13 [MethodImpl(MethodImplOptions.Synchronized)]
 14 public UnmanagedArray(int count)
 15 : base(count, Marshal.SizeOf(typeof(T)))
 16 {
 17 }
 18
 19 /// <summary>
 20 /// 获取或设置索引为<paramref name="index"/>的元素。
 21 /// </summary>
 22 /// <param name="index"></param>
 23 /// <returns></returns>
 24 public T this[int index]
 25 {
 26 get
 27 {
 28  if (index < 0 || index >= this.Count)
 29  throw new IndexOutOfRangeException("index of UnmanagedArray is out of range");
 30
 31  var pItem = this.Header + (index * elementSize);
 32  //var obj = Marshal.PtrToStructure(pItem, typeof(T));
 33  //T result = (T)obj;
 34  T result = Marshal.PtrToStructure<T>(pItem);// works in .net 4.5.1
 35  return result;
 36 }
 37 set
 38 {
 39  if (index < 0 || index >= this.Count)
 40  throw new IndexOutOfRangeException("index of UnmanagedArray is out of range");
 41
 42  var pItem = this.Header + (index * elementSize);
 43  //Marshal.StructureToPtr(value, pItem, true);
 44  Marshal.StructureToPtr<T>(value, pItem, true);// works in .net 4.5.1
 45 }
 46 }
 47
 48 /// <summary>
 49 /// 按索引顺序依次获取各个元素。
 50 /// </summary>
 51 /// <returns></returns>
 52 public IEnumerable<T> GetElements()
 53 {
 54 if (!this.disposed)
 55 {
 56  for (int i = 0; i < this.Count; i++)
 57  {
 58  yield return this[i];
 59  }
 60 }
 61 }
 62 }
 63
 64 /// <summary>
 65 /// 非托管数组的基类。
 66 /// </summary>
 67 public abstract class UnmanagedArrayBase : IDisposable
 68 {
 69
 70 /// <summary>
 71 /// 数组指针。
 72 /// </summary>
 73 public IntPtr Header { get; private set; }
 74
 75 /// <summary>
 76 /// 元素数目。
 77 /// </summary>
 78 public int Count { get; private set; }
 79
 80 /// <summary>
 81 /// 单个元素的字节数。
 82 /// </summary>
 83 protected int elementSize;
 84
 85 /// <summary>
 86 /// 申请到的字节数。（元素数目 * 单个元素的字节数）。
 87 /// </summary>
 88 public int ByteLength
 89 {
 90 get { return this.Count * this.elementSize; }
 91 }
 92
 93
 94 /// <summary>
 95 /// 非托管数组。
 96 /// </summary>
 97 /// <param name="elementCount">元素数目。</param>
 98 /// <param name="elementSize">单个元素的字节数。</param>
 99 [MethodImpl(MethodImplOptions.Synchronized)]
100 protected UnmanagedArrayBase(int elementCount, int elementSize)
101 {
102 this.Count = elementCount;
103 this.elementSize = elementSize;
104
105 int memSize = elementCount * elementSize;
106 this.Header = Marshal.AllocHGlobal(memSize);
107
108 allocatedArrays.Add(this);
109 }
110
111 private static readonly List<IDisposable> allocatedArrays = new List<IDisposable>();
112
113 /// <summary>
114 /// 立即释放所有<see cref="UnmanagedArray"/>。
115 /// </summary>
116 [MethodImpl(MethodImplOptions.Synchronized)]
117 public static void FreeAll()
118 {
119 foreach (var item in allocatedArrays)
120 {
121  item.Dispose();
122 }
123 allocatedArrays.Clear();
124 }
125
126 ~UnmanagedArrayBase()
127 {
128 Dispose();
129 }
130
131 #region IDisposable Members
132
133 /// <summary>
134 /// Internal variable which checks if Dispose has already been called
135 /// </summary>
136 protected Boolean disposed;
137
138 /// <summary>
139 /// Releases unmanaged and - optionally - managed resources
140 /// </summary>
141 /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
142 protected void Dispose(Boolean disposing)
143 {
144 if (disposed)
145 {
146  return;
147 }
148
149 if (disposing)
150 {
151  //Managed cleanup code here, while managed refs still valid
152 }
153 //Unmanaged cleanup code here
154 IntPtr ptr = this.Header;
155
156 if (ptr != IntPtr.Zero)
157 {
158  this.Count = 0;
159  this.Header = IntPtr.Zero;
160  Marshal.FreeHGlobal(ptr);
161 }
162
163 disposed = true;
164 }
165
166 /// <summary>
167 /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
168 /// </summary>
169 public void Dispose()
170 {
171 this.Dispose(true);
172 GC.SuppressFinalize(this);
173 }
174
175 #endregion
176
177 }

UnmanagedArray

如何使用(How to use)

UnmanagedArray<T>使用方式十分简单，就像一个普通的数组一样：

Using UnamangedAray<T> is just like a normal array(int[], vec3[], etc.):

internal static void TypicalScene()
 {
 const int count = 100;

 // 测试float类型
 var floatArray = new UnmanagedArray<float>(count);
 for (int i = 0; i < count; i++)
 {
 floatArray[i] = i;
 }
 for (int i = 0; i < count; i++)
 {
 var item = floatArray[i];
 if (item != i)
 { throw new Exception(); }
 }

 // 测试int类型
 var intArray = new UnmanagedArray<int>(count);
 for (int i = 0; i < count; i++)
 {
 intArray[i] = i;
 }
 for (int i = 0; i < count; i++)
 {
 var item = intArray[i];
 if (item != i)
 { throw new Exception(); }
 }

 // 测试bool类型
 var boolArray = new UnmanagedArray<bool>(count);
 for (int i = 0; i < count; i++)
 {
 boolArray[i] = i % 2 == 0;
 }
 for (int i = 0; i < count; i++)
 {
 var item = boolArray[i];
 if (item != (i % 2 == 0))
 { throw new Exception(); }
 }

 // 测试vec3类型
 var vec3Array = new UnmanagedArray<vec3>(count);
 for (int i = 0; i < count; i++)
 {
 vec3Array[i] = new vec3(i * 3 + 0, i * 3 + 1, i * 3 + 2);
 }
 for (int i = 0; i < count; i++)
 {
 var item = vec3Array[i];
 var old = new vec3(i * 3 + 0, i * 3 + 1, i * 3 + 2);
 if (item.x != old.x || item.y != old.y || item.z != old.z)
 { throw new Exception(); }
 }

 // 测试foreach
 foreach (var item in vec3Array.GetElements())
 {
 Console.WriteLine(item);
 }

 // 释放此数组占用的内存，这之后就不能再使用vec3Array了。
 vec3Array.Dispose();

 // 立即释放所有非托管数组占用的内存，这之后就不能再使用上面申请的数组了。
 UnmanagedArrayBase.FreeAll();
 }

快速读写UnmanagedArray<T>

UnmanagedArrayHelper

由于很多时候需要申请和使用很大的UnmanagedArray<T>，直接使用this[index]索引方式速度会偏慢，所以我添加了几个辅助方法，专门解决快速读写UnmanagedArray<T>的问题。

public static class UnmanagedArrayHelper
 {
 ///// <summary>
 ///// 错误 1 无法获取托管类型(“T”)的地址和大小，或无法声明指向它的指针
 ///// </summary>
 ///// <typeparam name="T"></typeparam>
 ///// <param name="array"></param>
 ///// <returns></returns>
 //public static unsafe T* FirstElement<T>(this UnmanagedArray<T> array) where T : struct
 //{
 // var header = (void*)array.Header;
 // return (T*)header;
 //}

 /// <summary>
 /// 获取非托管数组的第一个元素的地址。
 /// </summary>
 /// <param name="array"></param>
 /// <returns></returns>
 public static unsafe void* FirstElement(this UnmanagedArrayBase array)
 {
 var header = (void*)array.Header;

 return header;
 }

 public static unsafe void* LastElement(this UnmanagedArrayBase array)
 {
 var last = (void*)(array.Header + (array.ByteLength - array.ByteLength / array.Length));

 return last;
 }

 /// <summary>
 /// 获取非托管数组的最后一个元素的地址再向后一个单位的地址。
 /// </summary>
 /// <param name="array"></param>
 /// <returns></returns>
 public static unsafe void* TailAddress(this UnmanagedArrayBase array)
 {
 var tail = (void*)(array.Header + array.ByteLength);

 return tail;
 }
 }

如何使用

这个类型实现了3个扩展方法，可以获取UnmanagedArray<T>的第一个元素的位置、最后一个元素的位置、最后一个元素+1的位置。用这种unsafe的方法可以实现C语言一样的读写速度。

下面是一个例子。用unsafe的方式读写UnmanagedArray<T>，速度比this[index]方式快10到70倍。

public static void TypicalScene()
 {
 int length = 1000000;
 UnmanagedArray<int> array = new UnmanagedArray<int>(length);
 UnmanagedArray<int> array2 = new UnmanagedArray<int>(length);

 long tick = DateTime.Now.Ticks;
 for (int i = 0; i < length; i++)
 {
 array[i] = i;
 }
 long totalTicks = DateTime.Now.Ticks - tick;

 tick = DateTime.Now.Ticks;
 unsafe
 {
 int* header = (int*)array2.FirstElement();
 int* last = (int*)array2.LastElement();
 int* tailAddress = (int*)array2.TailAddress();
 int value = 0;
 for (int* ptr = header; ptr <= last/*or: ptr < tailAddress*/; ptr++)
 {
  *ptr = value++;
 }
 }
 long totalTicks2 = DateTime.Now.Ticks - tick;
 Console.WriteLine("ticks: {0}, {1}", totalTicks, totalTicks2);// unsafe method works faster.

 for (int i = 0; i < length; i++)
 {
 if (array[i] != i)
 {
  Console.WriteLine("something wrong here");
 }
 if (array2[i] != i)
 {
  Console.WriteLine("something wrong here");
 }
 }

 array.Dispose();
 array2.Dispose();
 }

unsafe
 {
  vec3* header = (vec3*)vec3Array.FirstElement();
  vec3* last = (vec3*)vec3Array.LastElement();
  vec3* tailAddress = (vec3*)vec3Array.TailAddress();
  int i = 0;
  for (vec3* ptr = header; ptr <= last/*or: ptr < tailAddress*/; ptr++)
  {
  *ptr = new vec3(i * 3 + 0, i * 3 + 1, i * 3 + 2);
  i++;
  }
  i = 0;
  for (vec3* ptr = header; ptr <= last/*or: ptr < tailAddress*/; ptr++, i++)
  {
  var item = *ptr;
  var old = new vec3(i * 3 + 0, i * 3 + 1, i * 3 + 2);
  if (item.x != old.x || item.y != old.y || item.z != old.z)
  { throw new Exception(); }
  }
 }

2015-08-25

用StructLayout和MarshalAs支持复杂的struct

在OpenGL中我需要用UnmanagedArray<mat4>，其中mat4定义如下：

1 /// <summary>
 2 /// Represents a 4x4 matrix.
 3 /// </summary>
 4 [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 4 * 4 * 4)]
 5 public struct mat4
 6 {
 7 /// <summary>
 8 /// Gets or sets the <see cref="vec4"/> column at the specified index.
 9 /// </summary>
10 /// <value>
11 /// The <see cref="vec4"/> column.
12 /// </value>
13 /// <param name="column">The column index.</param>
14 /// <returns>The column at index <paramref name="column"/>.</returns>
15 public vec4 this[int column]
16 {
17 get { return cols[column]; }
18 set { cols[column] = value; }
19 }
20
21 /// <summary>
22 /// Gets or sets the element at <paramref name="column"/> and <paramref name="row"/>.
23 /// </summary>
24 /// <value>
25 /// The element at <paramref name="column"/> and <paramref name="row"/>.
26 /// </value>
27 /// <param name="column">The column index.</param>
28 /// <param name="row">The row index.</param>
29 /// <returns>
30 /// The element at <paramref name="column"/> and <paramref name="row"/>.
31 /// </returns>
32 public float this[int column, int row]
33 {
34 get { return cols[column][row]; }
35 set { cols[column][row] = value; }
36 }
37
38 /// <summary>
39 /// The columms of the matrix.
40 /// </summary>
41 [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
42 private vec4[] cols;
43 }
44
45 /// <summary>
46 /// Represents a four dimensional vector.
47 /// </summary>
48 [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 4 * 4)]
49 public struct vec4
50 {
51 public float x;
52 public float y;
53 public float z;
54 public float w;
55
56 public float this[int index]
57 {
58 get
59 {
60  if (index == 0) return x;
61  else if (index == 1) return y;
62  else if (index == 2) return z;
63  else if (index == 3) return w;
64  else throw new Exception("Out of range.");
65 }
66 set
67 {
68  if (index == 0) x = value;
69  else if (index == 1) y = value;
70  else if (index == 2) z = value;
71  else if (index == 3) w = value;
72  else throw new Exception("Out of range.");
73 }
74 }
75 }

mat4

注意：UnmanagedArray<T>支持的struct，T的大小必须是确定的。所以在mat4里我们用 [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 4 * 4 * 4)] 指定mat4的大小为4个 vec4 * 4个 float * 4个字节(每个float) = 64字节，并且在 private vec4[] cols; 上用 [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)] 规定了cols的元素数必须是4。之后在 vec4 上的 [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 4 * 4)] 不写也可以，因为vec4只有4个简单的float字段，不含复杂类型。

下面是测试用例。

mat4 matrix = glm.scale(mat4.identity(), new vec3(2, 3, 4));

 var size = Marshal.SizeOf(typeof(mat4));
 size = Marshal.SizeOf(matrix);

 UnmanagedArray<mat4> array = new UnmanagedArray<mat4>(1);
 array[0] = matrix;

 mat4 newMatirx = array[0]; // newMatrix should be equal to matrix

 array.Dispose();

如果matrix和newMatrix相等，就说明上述Attribute配置正确了。

总结

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