不确定异步处理文件的正确方式

Question

我用这段代码在磁盘上写一组文件：

var savingTasks = games.Games.Select(t=>{
var path = Path.ChangeExtension(Path.Combine(savePath,Path.GetFileName(t.Url)),"pgn");
Log.Information($"trying to save game in:{path}");
var fs = new FileStream(path,FileMode.CreateNew,FileAccess.ReadWrite);
opened.Add(fs);
var sr = new StreamWriter(fs);
writers.Add(sr);
var tsk =  sr.WriteAsync(t.Pgn);
return tsk;
});
try
{
await Task.WhenAll(savingTasks);
var flushing = writers.Select(u=>u.FlushAsync());
await Task.WhenAll(flushing);
}
catch(Exception e)
{
Log.Fatal($"Cannot write to file:{e}");
throw e;
}
finally
{
opened.ForEach(s => s.Close());
}

在某些步骤中，即使代码运行得很好，我也不相信自己的做法是最好的。不能说服我的部分是我如何处理关闭：我在Select中创建了一组任务，但我必须跟踪打开的文件才能关闭它们(最后请参阅(，并且以类似的方式，我必须管理StreamWriter的集合(请参阅writers(。这并不能说服我，还有更好的方法吗？

Answer 1

你把事情搞得太复杂了。

您应该为FileStream和StreamWriter使用一个using块，该块负责处理它们时的冲洗/关闭。

通过等待WriteAsync而不是返回它生成的Task，将确保您的FileStream和StreamWriter不会过早处理：

var savingTasks = games.Games
.Select(async t =>
{
var path = Path.ChangeExtension(Path.Combine(savePath,Path.GetFileName(t.Url)),"pgn");
Log.Information($"trying to save game in:{path}");
using (var fs = new FileStream(path, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None, bufferSize: 4096, useAsync: true))
using (var sr = new StreamWriter(fs))
{
await sr.WriteAsync(t.Pgn);
}
});
try
{
await Task.WhenAll(savingTasks);
}
catch (Exception e)
{
Log.Fatal($"Cannot write to file:{e}");
throw;
}

Answer 2

我将把FlushAsync移到finally，因为如果在执行任务期间发生异常，它们将不会被清除。此外，为了保持清洁，我建议用一种方法做每件事，比如下一种：

var savingTasks = games.Games.Select(t=>ExecuteGameMethod(t));
try
{
await Task.WhenAll(savingTasks);
}
catch(Exception e)
{
Log.Fatal($"Cannot write to file:{e}");
throw;
}

public async Task ExecuteGameMethod(Game game)
{
var path = Path.ChangeExtension(Path.Combine(savePath,Path.GetFileName(game.Url)),"pgn");
Log.Information($"trying to save game in:{path}");
using(var fs = new FileStream(path,FileMode.CreateNew,FileAccess.ReadWrite,bufferSize:4096, isAsync:true ))
using(var sr = new StreamWriter(fs))
{
await sr.WriteAsync(game.Pgn);
await sr.FlushAsync();
}
}