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