C# 写入文件比较

数据长度：128188个long

BinaryWriter每次写一个long 耗时14.7828ms
StreamWriter每次写一个long 耗时44.0934 ms
FileStream每次写一个long 耗时20.5142 ms

FileStream固定chunk写入，循环操作数组，耗时13.4126 ms

	byte[] chunk = new byte[datalist.Count * 8];for (int i = 0; i < datalist.Count; i++) {long data = datalist[i];var bs = BitConverter.GetBytes(data);var startIndex = i * 8;for (int j = 0; j < 8; j++) {chunk[startIndex + j] = bs[j];}}fs.Write(chunk, 0, chunk.Length);startTime.Stop();lg.i($"{((float)startTime.ElapsedTicks / Stopwatch.Frequency) * 1000} ms");fs.Flush();fs.Close();

FileStream固定chunk写入,直接操作数组，耗时10.2729 ms

	byte[] chunk = new byte[datalist.Count * 8];for (int i = 0; i < datalist.Count; i++) {long data = datalist[i];var bs = BitConverter.GetBytes(data);var startIndex = i * 8;chunk[startIndex] = bs[0];chunk[startIndex + 1] = bs[1];chunk[startIndex + 2] = bs[2];chunk[startIndex + 3] = bs[3];chunk[startIndex + 4] = bs[4];chunk[startIndex + 5] = bs[5];chunk[startIndex + 6] = bs[6];chunk[startIndex + 7] = bs[7];}fs.Write(chunk, 0, chunk.Length);startTime.Stop();lg.i($"{((float)startTime.ElapsedTicks / Stopwatch.Frequency) * 1000} ms");fs.Flush();fs.Close();

经排查BitConverter.GetBytes源码如下，是上面比较耗时的地方，并且每次都会创建数组

public static unsafe byte[] GetBytes(long value) 
{byte[] bytes = new byte[8];fixed(byte* b = bytes)*((long*)b) = value;return bytes;
}

可以将上面改进一下，直接将代码内联进入上面代码上, 耗时2.8165 ms

public static unsafe byte[] GetBytes(List<long> values) {byte[] bytes = new byte[values.Count * sizeof(long)];fixed (byte* ptr = bytes) {long* longPtr = (long*)ptr;for (int i = 0; i < values.Count; i++) {*longPtr = values[i];longPtr++;}}return bytes;
}var startTime = new Stopwatch();
startTime.Start();
var fs = new FileStream(saveDataPath, FileMode.Append);
byte[] chunk = GetBytes(datalist);
fs.Write(chunk, 0, chunk.Length);
startTime.Stop();
lg.i($"{((float)startTime.ElapsedTicks / Stopwatch.Frequency) * 1000} ms");
fs.Flush();
fs.Close();