How to wait until File.Exists?

问题

I have an app, listening for the *.log file in a chosen folder. I used FileSystemWatcher.

But there is a problem. The other app responsible for making that file takes following steps:

Make a *.gz file
Unpack it to txt file (some random file name)
Change the *.txt name to proper one with *.log extension.

And I can not change this behaviour.

So I made 2 FileSystemWatchers for *.gz, and *.txt files. Why? Because this app sometimes doesn't unpack the gz file, and sometimes doesn't rename the txt file to the final *.log file.

FileSystemWatcher2 catches txt file, then (in the most cases it is renamed to log in the next 1000ms) I need to wait some time to check if txt file exists (if not, it seems to be renamed to the final *.log file).

The question is, how to check if file exists without Thread.Sleep() to prevent UI freeze?

I hope it is clear, if not I will try to describe it better. I think this is a complex problem.

Some code sample:

Watcher for gz file:

private void fileSystemWatcher_Created(object sender, FileSystemEventArgs e)
{
   //this is for gz files in case if gz file is not unpacked automatically by other app
   //I need to wait and check if gz was unpacked, if not, unpack it by myself,
   //then txt watcher will catch that
   Thread.Sleep(5000);
   if (File.Exists(e.FullPath))
   {
      try
      {
         byte[] dataBuffer = new byte[4096];
         using (System.IO.Stream fs = new FileStream(e.FullPath, 
                                                     FileMode.Open, 
                                                     FileAccess.Read))
         {
            using (GZipInputStream gzipStream = new GZipInputStream(fs))
            {                            
               string fnOut = Path.Combine(path_to_watcher, 
                                           Path.GetFileNameWithoutExtension(e.FullPath));

               using (FileStream fsOut = File.Create(fnOut))
               {
                  StreamUtils.Copy(gzipStream, fsOut, dataBuffer);
               }                            
            }
         }
      }
      catch { //Ignore }
   }
}

Watcher for txt file:

private void fileSystemWatcher2_Created(object sender, FileSystemEventArgs e)
{
   //this is for txt file
   Thread.Sleep(3500);
   if (File.Exists(e.FullPath))
   {
      //make my actions
   }
   else
   {
      //make my actions
   }
}

回答1:

Actually FileSystemWatcher Created event called in separate thread by .NET itself.. So basically you need to do absolutely nothing. Your code is OK as it is.

Here is the proof:

class Program
{
    static void Main(string[] args)
    {
        FileSystemWatcher fw = new FileSystemWatcher(@"C:\temp");
        fw.Created += fileSystemWatcher_Created;

        Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

        fw.EnableRaisingEvents = true;

        Console.ReadLine();
    }

    static void fileSystemWatcher_Created(object sender, FileSystemEventArgs e)
    {
        Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
    }
}

回答2:

You can use a BackGroundWorker to monitor the file system - and avoid freezing your UI

回答3:

You can use sleep without locking the UI thread, you essentially sleep a seperate thread.

public event EventHandler FileCreated;
public void CheckFileExists()
{
  while(!File.Exists(""))
  {
    Thread.Sleep(1000); 
  }
  FileCreated(this, new EventArgs());
}

Then call this as:

Thread t = new Thread(CheckFileExists);
this.FileCreated += new EventHandler(somemethod);
t.Start();

public void SomeMethod(object sender, EventArgs e)
{
  MessageBox.Show("File Created!");
}

Or as mentioned in another post use a BackGroundWorker in place of the seperate thread, put the code I mentioned into DoWork and listen for OnFinish event but seeing as there isn't that much work to do either methods are fine.

回答4:

int i = 0;
while (!File.Exists && i < 30) //limit the time to whait to 30 sec
{
    Threed.Sleep(1000);
    File.Refresh();
    i++;
}

来源：https://stackoverflow.com/questions/14816425/how-to-wait-until-file-exists

标签

multithreading

file

sleep

exists