这里的解决方案并不适合我。我拿了 user3902302 的答案，这又是基于 bigtech 的答案并写了一个完整的课程。另外，我没有使用 StreamWriter，您可以更改一行（针对 StreamWrite 等效项的 AppendAllText）。
几乎没有错误处理（例如，当它失败时重试访问，尽管锁应该捕获所有内部并发访问）。
对于一些以前不得不使用像 log4net 或 nlog 这样的大型解决方案的人来说，这可能就足够了。（而且 log4net RollingAppender 甚至不是线程安全的，这个是。:)）
public class RollingLogger
{
readonly static string LOG_FILE = @"c:\temp\logfile.log";
readonly static int MaxRolledLogCount = 3;
readonly static int MaxLogSize = 1024; // 1 * 1024 * 1024; <- small value for testing that it works, you can try yourself, and then use a reasonable size, like 1M-10M
public static void LogMessage(string msg)
{
lock (LOG_FILE) // lock is optional, but.. should this ever be called by multiple threads, it is safer
{
RollLogFile(LOG_FILE);
File.AppendAllText(LOG_FILE, msg + Environment.NewLine, Encoding.UTF8);
}
}
private static void RollLogFile(string logFilePath)
{
try
{
var length = new FileInfo(logFilePath).Length;
if (length > MaxLogSize)
{
var path = Path.GetDirectoryName(logFilePath);
var wildLogName = Path.GetFileNameWithoutExtension(logFilePath) + "*" + Path.GetExtension(logFilePath);
var bareLogFilePath = Path.Combine(path, Path.GetFileNameWithoutExtension(logFilePath));
string[] logFileList = Directory.GetFiles(path, wildLogName, SearchOption.TopDirectoryOnly);
if (logFileList.Length > 0)
{
// only take files like logfilename.log and logfilename.0.log, so there also can be a maximum of 10 additional rolled files (0..9)
var rolledLogFileList = logFileList.Where(fileName => fileName.Length == (logFilePath.Length + 2)).ToArray();
Array.Sort(rolledLogFileList, 0, rolledLogFileList.Length);
if (rolledLogFileList.Length >= MaxRolledLogCount)
{
File.Delete(rolledLogFileList[MaxRolledLogCount - 1]);
var list = rolledLogFileList.ToList();
list.RemoveAt(MaxRolledLogCount - 1);
rolledLogFileList = list.ToArray();
}
// move remaining rolled files
for (int i = rolledLogFileList.Length; i > 0; --i)
File.Move(rolledLogFileList[i - 1], bareLogFilePath + "." + i + Path.GetExtension(logFilePath));
var targetPath = bareLogFilePath + ".0" + Path.GetExtension(logFilePath);
// move original file
File.Move(logFilePath, targetPath);
}
}
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.ToString());
}
}
}
编辑：
因为我刚刚注意到你问了一个稍微不同的问题：如果你的线条大小差异很大，这将是一个变化（虽然在 90% 的情况下不会比你的有所改善，并且可能会稍微快一点，还引入了一个新的未处理错误（\n 不存在））：
private static void PerformFileTrim(string filename)
{
var fileSize = (new System.IO.FileInfo(filename)).Length;
if (fileSize > 5000000)
{
var text = File.ReadAllText(filename);
var amountToCull = (int)(text.Length * 0.33);
amountToCull = text.IndexOf('\n', amountToCull);
var trimmedText = text.Substring(amountToCull + 1);
File.WriteAllText(filename, trimmedText);
}
}