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();
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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();

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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;
}
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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();

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