我目前在旧的Backgroundworker
类视图中编写了一个简单的事件记录器。我试图将其转换为TPL实现。
我没有足够的使用C#中的线程来真正优先于另一个,但我知道TPL正变得越来越受欢迎,我想尽可能地坚持下去。另一个原因是,使用当前代码,我找不到一个简单的方法来使EventLog
类线程安全。我发现自己使用BeginInvoke
从非UI线程写入日志,这对我来说似乎很麻烦。
所以这是原始代码。
public class EventLog
{
public String LogPath { get; set; }
public List<LogEvent> Events { get; private set; }
public static EventLog Instance { get { return lazyInstance.Value; } }
private static readonly Lazy<EventLog> lazyInstance = new Lazy<EventLog>(() => new EventLog());
private EventLog()
{
Events = new List<LogEvent>();
LogPath = Assembly.GetExecutingAssembly().CodeBase;
LogPath = Path.GetDirectoryName(LogPath);
LogPath = LogPath.Replace("file:\\", "");
LogPath = LogPath + "\\Log.txt";
}
public override void publish(LogEvent newEvent)
{
Events.Add(newEvent);
if (!LogEventWriter.Instance.IsBusy)
LogEventWriter.Instance.RunWorkerAsync(LogPath);
LogEventWriter.Instance.LogEvents.Add(newEvent);
}
}
internal class LogEventWriter : BackgroundWorker
{
public BlockingCollection<LogEvent> LogEvents { get; set; }
public static LogEventWriter Instance { get { return lazyInstance.Value; } }
private static readonly Lazy<LogEventWriter> lazyInstance = new Lazy<LogEventWriter>(() => new LogEventWriter());
private LogEventWriter()
{
WorkerSupportsCancellation = true;
LogEvents = new BlockingCollection<LogEvent>();
}
protected override void OnDoWork(DoWorkEventArgs e)
{
if (e.Argument != null && e.Argument is String)
{
String logPath = (String)e.Argument;
using (StreamWriter logFile = new StreamWriter(logPath, true))
{
while (!CancellationPending)
{
LogEvent anEvent = LogEvents.Take();
logFile.WriteLine(anEvent.Message);
logFile.Flush();
if (anEvent.Message.Contains("Application Terminated"))
break;
}
logFile.Close();
}
}
e.Cancel = true;
}
}
我对日志的当前思路是在系统出现故障时尽快将日志写入文件,以便日志尽可能多地获取信息。这就是Backgroundworker
的用途。我还在List<LogEvent>
类中保留了EventLog
,以便用户可以在当前日志中搜索特定事件(未完全实现/抛光)。
这是我目前的TPL解决方案。我尽力将日志记录功能包装到Task
s但我仍然觉得我应该有一个类似于publish
的函数而不必直接将LogEvent
s放入BlockingCollection<>
以便我可以在一个单独的线程上运行日志记录主UI。
还有一个更清洁的方法来阻止Task
s而不必从他们的循环向他们发送“特殊”LogEvent
到break
?
public class EventLog
{
public static EventLog Instance { get { return lazyInstance.Value; } }
private static readonly Lazy<EventLog> lazyInstance = new Lazy<EventLog>(() => new EventLog());
public String LogPath { get; set; }
public ConcurrentQueue<LogEvent> Events { get; set; }
private EventLog()
{
Events = new ConcurrentQueue<LogEvent>();
WriteQueue = new BlockingCollection<LogEvent>();
LogEventQueue = new BlockingCollection<LogEvent>();
LogPath = Assembly.GetExecutingAssembly().CodeBase;
LogPath = Path.GetDirectoryName(LogPath);
LogPath = LogPath.Replace("file:\\", "");
LogPath = LogPath + "\\LogASDF.txt";
StartManager();
StartWriter();
}
public BlockingCollection<LogEvent> LogEventQueue { get; set; }
private void StartManager()
{
var writeTask = Task.Factory.StartNew(() =>
{
while (true)
{
LogEvent anEvent = LogEventQueue.Take();
Events.Enqueue(anEvent);
WriteQueue.Add(anEvent);
if (anEvent.Message.Contains("Application Terminated"))
break;
}
});
}
private BlockingCollection<LogEvent> WriteQueue { get; set; }
private void StartWriter()
{
var writeTask = Task.Factory.StartNew(() =>
{
using (StreamWriter logFile = new StreamWriter(LogPath, true))
{
while(true)
{
LogEvent anEvent = WriteQueue.Take();
logFile.WriteLine(anEvent.Message);
logFile.Flush();
if (anEvent.Message.Contains("Application Terminated"))
break;
}
logFile.Close();
}
});
}
}
CancellationToken
取消这两项任务?我不知道如果BlockingCollection
阻塞,我总是必须“脉冲”该集合以使其解锁。LogEvent
插入日志而无需直接插入LogEventQueue
?现在你的代码不是thread-safe
,因为你有这个:
public List<LogEvent> Events { get; private set; }
List<T>
不是线程安全的,可以从外部代码更改。而且我看不出它是否被使用过。
此外,你真的应该在你的代码中使用CancellationToken
,因为在其他情况下你会遇到麻烦:例如,你有5条消息在队列中,你决定取消你的工作。在这种情况下,检查Shutdown Log
只会在一段时间后中断循环,这会让您的班级最终用户感到困惑。
此外,BlockingCollection<T>.Take
方法与CancellationToken
有一个超载,但如果取消你将获得OperationCanceledException
:
try
{
LogEvent anEvent = WriteQueue.Take(CancellationPending);
}
catch (OperationCanceledException ex)
{
// handle stop here;
}
在多线程的非常糟糕的实践中无限循环,我建议不要使用它。
以下是我使用.net 4.5处理此问题的方法。对事件队列的所有访问都是同步的,因此不需要锁定或同步:
public class EventLog
{
public String LogPath { get; set; }
public List<LogEvent> Events {get;set;}
private isProcessing = false;
public CancellationTokenSource cts = new CancellationTokenSource();
private CancellationToken _token;
public static EventLog Instance { get { return lazyInstance.Value; } }
private static readonly Lazy<EventLog> lazyInstance = new Lazy<EventLog>(() => new EventLog());
private EventLog()
{
Events = new List<LogEvent>();
Events.CollectionChanged += Events_CollectionChanged;
LogPath = Assembly.GetExecutingAssembly().CodeBase;
LogPath = Path.GetDirectoryName(LogPath);
LogPath = LogPath.Replace("file:\\", "");
LogPath = LogPath + "\\Log.txt";
_token = cts.Token;
}
public override void publish(LogEvent newEvent)
{
Events.Add(newEvent);
if (!isProcessing)
ProcessLog();
}
private async void ProcessLog()
{
while (Events.Count > 0)
{
isProcessing = true;
LogEvent e = EventLogs.First();
await Task.Run (() => { WriteLog(e,token); },_token);
EventLogs.Remove(e);
if (_token.IsCancellationRequested == true)
EventLogs.Clear();
}
isProcessing = false;
}
private void WriteLog(LogEvent e,CancellationToken token)
{
using (StreamWriter logFile = new StreamWriter(LogPath, true))
{
if (token.IsCancellationRequested == false)
{
logFile.WriteLine(e.Message);
logFile.Flush();
}
}
}
}
编辑:添加了取消令牌。编辑2:添加了WriteLog功能。