我有一个Windows窗体应用程序，可以复制和重新调整GEDCOM族谱文件中的图像引用。用户从主窗体中选择文件和输出目录以及重新调整大小的选项，然后打开另一个窗体作为包含标签，进度条和按钮的对话框。我正在更新应用程序以使用.NET 4.5中的新异步功能，并修改它以使用并行处理。一切都很好，除了我注意到UI响应有点不稳定（断断续续）;如果我没有用百分比更新消息标签，那么它会更顺畅。此外，当我取消任务时，UI将挂起1至15秒。该应用程序仅供我个人使用，所以这并不是什么大不了的事，但我很好奇可能导致问题的原因以及推荐的处理方法是什么。并行处理是否会因为处理太多线程而使CPU过载？我尝试在每次循环迭代中添加一个Thread.Sleep（100），它似乎有点帮助。
以下是仍然会导致问题的最小版本的应用程序。重现：
- 使用以下表单创建一个新的Windows窗体应用程序。
- 使用一堆jpeg图像（50多张图像）创建一个目录
- 将_SourceDirectoryPath和_DestinationDirectoryPath变量替换为您的目录。
- 运行应用程序
Designer.cs：
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.lblMessage = new System.Windows.Forms.Label();
this.pgProgressBar = new System.Windows.Forms.ProgressBar();
this.btnStart = new System.Windows.Forms.Button();
this.btnCancel = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// lblMessage
//
this.lblMessage.AutoSize = true;
this.lblMessage.Location = new System.Drawing.Point(32, 25);
this.lblMessage.Name = "lblMessage";
this.lblMessage.Size = new System.Drawing.Size(0, 13);
this.lblMessage.TabIndex = 0;
//
// pgProgressBar
//
this.pgProgressBar.Location = new System.Drawing.Point(35, 51);
this.pgProgressBar.Name = "pgProgressBar";
this.pgProgressBar.Size = new System.Drawing.Size(253, 23);
this.pgProgressBar.TabIndex = 1;
//
// btnStart
//
this.btnStart.Location = new System.Drawing.Point(132, 97);
this.btnStart.Name = "btnStart";
this.btnStart.Size = new System.Drawing.Size(75, 23);
this.btnStart.TabIndex = 2;
this.btnStart.Text = "Start";
this.btnStart.UseVisualStyleBackColor = true;
this.btnStart.Click += new System.EventHandler(this.btnStart_Click);
//
// btnCancel
//
this.btnCancel.Location = new System.Drawing.Point(213, 97);
this.btnCancel.Name = "btnCancel";
this.btnCancel.Size = new System.Drawing.Size(75, 23);
this.btnCancel.TabIndex = 3;
this.btnCancel.Text = "Cancel";
this.btnCancel.UseVisualStyleBackColor = true;
this.btnCancel.Click += new System.EventHandler(this.btnCancel_Click);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(315, 149);
this.Controls.Add(this.btnCancel);
this.Controls.Add(this.btnStart);
this.Controls.Add(this.pgProgressBar);
this.Controls.Add(this.lblMessage);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.Label lblMessage;
private System.Windows.Forms.ProgressBar pgProgressBar;
private System.Windows.Forms.Button btnStart;
private System.Windows.Forms.Button btnCancel;
}
代码：
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
public partial class Form1 : Form
{
private CancellationTokenSource _CancelSource;
private string _SourceDirectoryPath = @"Your\Source\Directory";
private string _DestinationDirectoryPath = @"Your\Destination\Directory";
public Form1()
{
InitializeComponent();
lblMessage.Text = "Click Start to begin extracting images";
btnCancel.Enabled = false;
_CancelSource = new CancellationTokenSource();
}
private async void btnStart_Click(object sender, EventArgs e)
{
btnStart.Enabled = false;
btnCancel.Enabled = true;
List<string> files = await Task.Run(() => Directory.GetFiles(_SourceDirectoryPath, "*.jpg").ToList());
// scan/extract files
Progress<int> progress = new Progress<int>(UpdateProgress);
int result = await Task.Run(() => ExtractFiles(files, progress, _CancelSource.Token));
if (_CancelSource.IsCancellationRequested)
{
lblMessage.Text = "Extraction cancelled by user.";
}
else
{
lblMessage.Text = string.Format("Extraction Complete: {0} files extracted.", result);
}
btnStart.Enabled = true;
btnCancel.Enabled = false;
}
private void btnCancel_Click(object sender, EventArgs e)
{
lblMessage.Text = "Cancelling...";
btnCancel.Enabled = false;
_CancelSource.Cancel();
}
private void UpdateProgress(int value)
{
lblMessage.Text = string.Format("Extracting files: {0}%", value);
pgProgressBar.Value = value;
}
public int ExtractFiles(List<string> fileReferences, IProgress<int> progress, CancellationToken cancelToken)
{
double totalFiles = fileReferences.Count;
int processedCount = 0;
int extractedCount = 0;
int previousPercent = 0;
Directory.CreateDirectory(_DestinationDirectoryPath);
Parallel.ForEach(fileReferences, (reference, state) =>
{
if (cancelToken.IsCancellationRequested)
{
state.Break();
}
string fileName = Path.GetFileName(reference);
string filePath = Path.Combine(_DestinationDirectoryPath, fileName);
using (Image image = Image.FromFile(reference))
{
using (Image newImage = ResizeImage(image, 1000, 1000))
{
newImage.Save(filePath);
Interlocked.Increment(ref extractedCount);
}
}
Interlocked.Increment(ref processedCount);
int percent = (int)(processedCount / totalFiles * 100);
if (percent > previousPercent)
{
progress.Report(percent);
Interlocked.Exchange(ref previousPercent, percent);
}
});
return extractedCount;
}
public Image ResizeImage(Image image, int maxWidth, int maxHeight)
{
Image newImage = null;
if (image.Width > maxWidth || image.Height > maxHeight)
{
double widthRatio = (double)maxWidth / (double)image.Width;
double heightRatio = (double)maxHeight / (double)image.Height;
double ratio = Math.Min(widthRatio, heightRatio);
int newWidth = (int)(image.Width * ratio);
int newHeight = (int)(image.Height * ratio);
newImage = new Bitmap(newWidth, newHeight);
using (Graphics graphic = Graphics.FromImage(newImage))
{
graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
graphic.DrawImage(image, 0, 0, newWidth, newHeight);
}
}
return newImage;
}
}
答案 0 :(得分：0)
我可以在这里看到两个潜在的问题：
_CancelSource.Cancel()阻止了UI线程。您可以取消作为异步任务。查看相关帖子：Why does cancellation block for so long when cancelling a lot of HTTP requests?。对于CPU过载，这也是可能的。您可以使用分析器来检查CPU使用情况。 Visual Studio有一个集成的profiler，可以很好地与C＃配合使用。
答案 1 :(得分：0)
我相信我发现了这个问题。在后台线程中调用Graphics.DrawImage()时，UI线程中的GDI +被阻止。见Why do Graphics operations in background thread block Graphics operations in main UI thread?
一个明显的解决方案是使用多个流程（参见：Parallelizing GDI+ Image Resizing .net）