c# - 使用 FileSystemWatcher 时 c# GUI 中的内存不足异常 - 多线程

Question

我构建了一个 windows-forms-app，每当图像在我使用 FileSystemWatcher 观察的特定目录中创建时，我(尝试)对图像进行大量计算。

private void OnNewFileInDir(object source, FileSystemEventArgs evtArgs) 
{  
  //Load the actual image:
  imageFilepath = evtArgs.FullPath;  //imageFilepath is a private class string var
  Image currentImage = Image.FromFile(imageFilepath);

  //Display the image in the picture box:
  UpdatePictureBox(currentImage);     //Method to update the GUI with invoking for the UI thread

  //Extensive Calculation on the images
  Image currentResultImage = DoExtensiveWork(currentImage);

  // Put the current result in the picture box
  UpdatePictureBox(currentResultImage );

  //dispose the current/temporary image
  currentImage.Dispose();
}

将新文件粘贴到目录时会正确触发该事件。但是我在线上收到“System.OutOfMemoryException”

Image currentImage = Image.FromFile(imageFilepath);

当我将此代码(使用相同的文件路径)准确地放入按钮事件中(因此不使用 FileSystemWatcher)时，一切正常。所以我认为线程存在一些问题，因为大量计算是由 FileSystemWatcher-Thread 而不是 UI 线程调用的。

我试过这样的事情:

//TRY 1: By executing a button click method containg the code
pb_Calculate_Click(this, new EventArgs());    //This does not work eigther --> seems to be a problem with "Who is calling the method"

//TRY 2: Open a new dedicated thread for doing the work of the HistoCAD calculations
Thread newThread_OnNewFile = new Thread(autoCalcAndDisplay);
newThread_OnNewFile.Start();


//TRY 3: Use a background worker as a more safe threading method(?)
using (BackgroundWorker bw = new BackgroundWorker())
{
   bw.DoWork += new DoWorkEventHandler(bw_DoWork);
   if (bw.IsBusy == false)
   {
      bw.RunWorkerAsync();
   }
}

不幸的是，它们都不可靠。第一根本没有。第 2 个有时会起作用，第 3 个也会起作用。

你们中有人知道那里发生了什么吗？我该怎么做才能使其正常工作？谢谢!

编辑:感谢您的评论:我还尝试在每个事件上调用 GC.collect() 并尝试尽可能包含 using() 和 dispose() 。当我手动(使用按钮)执行该过程时，即使一个接一个地处理大量文件，它也能正常工作。但是当使用事件处理程序完成时，我有时会在我复制到文件夹中的第一个文件上得到 outOfMem-Exception。文件始终是相同的 BMP，大小为 32MB。这是处理一张图像的内存使用情况:

编辑 2:我创建了一个最小的示例(带有一个图片框和一个按钮样式的复选框的 GUI)。事实证明，同样的事情正在发生。 OutOfMemException 发生在同一行(图片...)。特别是对于大型 BMP，异常几乎总是发生:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace MinimalExampleTesting
{
    public partial class Form1 : Form
    {
        private string imageFilepath;
        private string autoModePath = @"C:\Users\Tim\Desktop\bmpordner";

        //Define a filesystem watcher object
        private FileSystemWatcher watcher;

        public Form1()
        {
            InitializeComponent();


            /*** Creating as FileSystemEventArgs watcher in order to monitor a specific folder ***/
            watcher = new FileSystemWatcher();
            Console.WriteLine(watcher.Path);
            // set the path if already exists, otherwise we have to wait for it to be set
            if (autoModePath != null)
                watcher.Path = autoModePath;
            // Watch for changes in LastAccess and LastWrite times and renaming of files or directories.
            watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
               | NotifyFilters.FileName | NotifyFilters.DirectoryName;
            // Only watch for BMP files.
            watcher.Filter = "*.bmp";
            // Add event handler. Only on created, not for renamed, changed or something
            // Get into the list of the watcher. Watcher fires event and "OnNewFileCreatedInDir" will be called
            watcher.Created += new FileSystemEventHandler(OnNewFileInDir);


        }

        private void tb_AutoMode_CheckedChanged(object sender, EventArgs e)
        {

            //First of all test if the auto mode path is set and correctly exists currently:
            if (!Directory.Exists(autoModePath) || autoModePath == null)
            {
                MessageBox.Show("Check if Auto Mode path is correctly set and if path exists",
                    "Error: Auto Mode Path not found");
                return;
            }

            // Begin watching if the AutoModePath was at least set
            if (autoModePath != null)
            {
                watcher.EnableRaisingEvents = tb_AutoMode.Checked;  //Since we have a toogle butten, we can use the 'checked' state to enable or disable the automode
            }

        }


        private void OnNewFileInDir(object source, FileSystemEventArgs evtArgs)
        {
            Console.WriteLine("New file in detected: " + evtArgs.FullPath);

            //Force a garbage collection on every new event to free memory and also compact mem by removing fragmentation.
            GC.Collect();

            //Set the current filepath in the class with path of the file added to the folder:
            imageFilepath = evtArgs.FullPath;

            //Load the actual image:
            Image currentImage = Image.FromFile(imageFilepath);

            UpdatePictureBox(currentImage);

        }

        private void UpdatePictureBox(Image img)
        {
            if (pictureBox_Main.InvokeRequired)
            {
                MethodInvoker mi = delegate
                {
                    pictureBox_Main.Image = img;
                    pictureBox_Main.Refresh();
                };
                pictureBox_Main.Invoke(mi);
            }
            else {  //Otherwise (when the calculation is perfomed by the GUI-thread itself) no invoke necessary
                pictureBox_Main.Image = img;
                pictureBox_Main.Refresh();
            }
            img.Dispose();
        }

    }
}

提前感谢进一步的提示:)

Answer 1

已解决:

问题似乎是，该事件会立即触发，但文件尚未最终复制。这意味着我们必须等到文件可用。事件开始时的 Thread.Sleep(100) 完成这项工作。正如我现在知道要用谷歌搜索什么，我找到了两个链接: This和 this在哪里可以找到:

The OnCreated event is raised as soon as a file is created. If a file is being copied or transferred into a watched directory, the OnCreated event will be raised immediately, followed by one or more OnChanged events

因此，最适合我的情况是包含一种方法来测试文件是否仍处于锁定状态，而不是在事件开始时等待文件解锁。不需要额外的线程或 BackgroundWorker。看代码:

private void OnNewFileInDir(object source, FileSystemEventArgs evtArgs)
{
   Console.WriteLine("New file detected: " + evtArgs.FullPath);

   //Wait for the file to be free
   FileInfo fInfo = new FileInfo(evtArgs.FullPath);
   while (IsFileLocked(fInfo))
   {
       Console.WriteLine("File not ready to use yet (copy process ongoing)");
       Thread.Sleep(5);  //Wait for 5ms
   }

   //Set the current filepath in the class with path of the file added to the folder:
   imageFilepath = evtArgs.FullPath;
   //Load the actual image:
   Image currentImage = Image.FromFile(imageFilepath);    
   UpdatePictureBox(currentImage);
}

private static bool IsFileLocked(FileInfo file)
{
    FileStream stream = null;
    try
    {
        //try to get a file lock
        stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
    }
    catch (IOException)
    {
       //File isn't ready yet, so return true as it is still looked --> we need to keep on waiting
       return true;
    }
    finally
    {
        if (stream != null){ 
            stream.Close();
            stream.Dispose();
        }
    }
    // At the end, when stream is closed and disposed and no exception occured, return false --> File is not locked anymore
    return false;
}

尽管如此:感谢您的帮助……它让我走上了正确的轨道；)