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

程序员文章站 2022-04-12 23:08:16
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 alloca...

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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