90 lines
4.1 KiB
XML
90 lines
4.1 KiB
XML
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<?xml version="1.0"?>
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<clause number="25.8" title="Dynamic memory allocation">
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<paragraph>Except for the stackalloc operator, C# provides no predefined constructs for managing non-garbage collected memory. Such services are typically provided by supporting class libraries or imported directly from the underlying operating system. <example>[Example: For example, the Memory class below illustrates how the heap functions of an underlying operating system might be accessed from C#: <code_example><![CDATA[
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using System;
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using System.Runtime.InteropServices;
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public unsafe class Memory
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{
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// Handle for the process heap. This handle is used in all calls to
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the
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// HeapXXX APIs in the methods below.
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static int ph = GetProcessHeap();
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// Private instance constructor to prevent instantiation.
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private Memory() {}
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// Allocates a memory block of the given size. The allocated memory is
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// automatically initialized to zero.
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public static void* Alloc(int size) {
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void* result = HeapAlloc(ph, HEAP_ZERO_MEMORY, size);
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if (result == null) throw new OutOfMemoryException();
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return result;
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}
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// Copies count bytes from src to dst. The source and destination
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// blocks are permitted to overlap.
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public static void Copy(void* src, void* dst, int count) {
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byte* ps = (byte*)src;
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byte* pd = (byte*)dst;
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if (ps > pd) {
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for (; count != 0; count--) *pd++ = *ps++;
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}
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else if (ps < pd) {
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for (ps += count, pd += count; count != 0; count--) *--pd = *--
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ps;
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}
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}
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// Frees a memory block.
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public static void Free(void* block) {
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if (!HeapFree(ph, 0, block)) throw new InvalidOperationException();
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}
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// Re-allocates a memory block. If the reallocation request is for a
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// larger size, the additional region of memory is automatically
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// initialized to zero.
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public static void* ReAlloc(void* block, int size) {
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void* result = HeapReAlloc(ph, HEAP_ZERO_MEMORY, block, size);
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if (result == null) throw new OutOfMemoryException();
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return result;
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}
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// Returns the size of a memory block.
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public static int SizeOf(void* block) {
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int result = HeapSize(ph, 0, block);
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if (result == -1) throw new InvalidOperationException();
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return result;
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}
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// Heap API flags
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const int HEAP_ZERO_MEMORY = 0x00000008;
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// Heap API functions
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[DllImport("kernel32")]
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static extern int GetProcessHeap();
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[DllImport("kernel32")]
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static extern void* HeapAlloc(int hHeap, int flags, int size);
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[DllImport("kernel32")]
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static extern bool HeapFree(int hHeap, int flags, void* block);
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[DllImport("kernel32")]
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static extern void* HeapReAlloc(int hHeap, int flags,
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void* block, int size);
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[DllImport("kernel32")]
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static extern int HeapSize(int hHeap, int flags, void* block);
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}
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]]></code_example></example></paragraph>
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<paragraph>
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<example>An example that uses the Memory class is given below: <code_example><![CDATA[
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class Test
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{
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static void Main() {
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unsafe {
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byte* buffer = (byte*)Memory.Alloc(256);
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for (int i = 0; i < 256; i++) buffer[i] = (byte)i;
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byte[] array = new byte[256];
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fixed (byte* p = array) Memory.Copy(buffer, p, 256);
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Memory.Free(buffer);
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for (int i = 0; i < 256; i++) Console.WriteLine(array[i]);
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}
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}
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}
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]]></code_example></example>
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</paragraph>
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<paragraph>
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<example>The example allocates 256 bytes of memory through Memory.Alloc and initializes the memory block with values increasing from 0 to 255. It then allocates a 256-element <keyword>byte</keyword> array and uses Memory.Copy to copy the contents of the memory block into the <keyword>byte</keyword> array. Finally, the memory block is freed using Memory.Free and the contents of the <keyword>byte</keyword> array are output on the console. end example]</example>
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</paragraph>
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<paragraph>End of conditionally normative text. </paragraph>
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</clause>
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