统计一个大文本行数的几种方法以及效率统计（二）

.NET4.0 + MemoryMapping + ReadByte()

该方法的思路主要是通过内存映射的原理，访问文件内容，由于在.net环境下不能一次性映射太大的文件，所以仍然采用分块映射的方式：

主要代码如下：

        /// <summary>
        /// MemoryMapping + ReadByte()
        /// </summary>
        unsafe static void CalulateLine_MemoryMapping_ReadByte(uint oneBlockSize)
        {
            const string FILE_MAPPING_NAME = "~MappingTemp";
            const int LINE_MIN_SIZE = 30;

            long lineCount = 0;

            IntPtr fileHandle = ShareMemory.CreateFile(
                FILE_NAME,
                ShareMemory.GENERIC_READ | ShareMemory.GENERIC_WRITE,
                FileShare.Read | FileShare.Write,
                IntPtr.Zero,
                FileMode.Open,
                ShareMemory.FILE_ATTRIBUTE_NORMAL | ShareMemory.FILE_FLAG_SEQUENTIAL_SCAN,
                IntPtr.Zero);

            uint fileSize = ShareMemory.GetFileSize(fileHandle, IntPtr.Zero);

            if (ShareMemory.INVALID_HANDLE_VALUE != (int)fileHandle)
            {
                IntPtr mappingHandle = ShareMemory.CreateFileMapping(
                    (int)fileHandle,
                    IntPtr.Zero,
                    ShareMemory.PAGE_READWRITE,
                    0,
                    0,
                    FILE_MAPPING_NAME);
                if (mappingHandle != IntPtr.Zero)
                {
                    uint mapFlag = 0;

                    while (mapFlag <= fileSize)
                    {
                        uint eachMappingSize = oneBlockSize;
                        if (fileSize - mapFlag < oneBlockSize)
                        {
                            eachMappingSize = fileSize - mapFlag;
                        }

                        IntPtr pHead = ShareMemory.MapViewOfFile(
                        mappingHandle,
                        (uint)(ShareMemory.FILE_MAP_READ),
                        0,
                        mapFlag,
                        eachMappingSize);

                        int lastError = ShareMemory.GetLastError();

                        if (pHead != IntPtr.Zero)
                        {

                            long flag = 0;
                            while (flag < eachMappingSize)
                            {
                                //byte* pbHead= (byte*)pHead;
                                //byte temp = *(pbHead + flag);

                                byte temp = Marshal.ReadByte((IntPtr)((int)pHead + flag));

                                if (temp == 0x0D)
                                {
                                    lineCount++;
                                    flag += LINE_MIN_SIZE;
                                }
                                flag++;
                            }

                            ShareMemory.UnmapViewOfFile(pHead);
                        }
                        mapFlag += oneBlockSize;
                    }

                    ShareMemory.CloseHandle(mappingHandle);
                }
                ShareMemory.CloseHandle(fileHandle);

            }
        }

测试结果：

.NET4.0 + MemoryMapping + Unsafe

使用unsafe代码，就是在上面代码的基础上，做了一些简单的修改。

byte* pbHead = (byte*)pHead;
byte temp = *(pbHead + flag);

测试结果：