ASP.net C# 文件被另一个进程使用

Question

我使用以下页面创建缩略图，Thumbnail.ashx：

<%@ WebHandler Language="C#" Class="Thumbnail" %>

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Web;

public class Thumbnail : IHttpHandler {

    private int _thumbnailSize = 150;

    public void ProcessRequest(HttpContext context) {
        string photoName = context.Request.QueryString["p"];

        string cachePath = Path.Combine(HttpRuntime.CodegenDir, photoName + ".png");
        if (File.Exists(cachePath)) {
            OutputCacheResponse(context, File.GetLastWriteTime(cachePath));
            context.Response.WriteFile(cachePath);
            return;
        }
        string photoPath = context.Server.MapPath("../uploads/originals/" + photoName);
        Bitmap photo;
        try {
            photo = new Bitmap(photoPath);
        }
        catch (ArgumentException) {
            throw new HttpException(404, "Photo not found.");
        }
        context.Response.ContentType = "image/png";
        int width, height;
        if (photo.Width > photo.Height) {
            width = _thumbnailSize;
            height = photo.Height * _thumbnailSize / photo.Width;
        }
        else {
            width = photo.Width * _thumbnailSize / photo.Height;
            height = _thumbnailSize;
        }
        Bitmap target = new Bitmap(width, height);
        using (Graphics graphics = Graphics.FromImage(target)) {
            graphics.CompositingQuality = CompositingQuality.HighSpeed;
            graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
            graphics.CompositingMode = CompositingMode.SourceCopy;
            graphics.DrawImage(photo, 0, 0, width, height);
            using (MemoryStream memoryStream = new MemoryStream()) {
                target.Save(memoryStream, ImageFormat.Png);
                OutputCacheResponse(context, File.GetLastWriteTime(photoPath));
                using (FileStream diskCacheStream = new FileStream(cachePath, FileMode.CreateNew)) {
                    memoryStream.WriteTo(diskCacheStream);
                }
                memoryStream.WriteTo(context.Response.OutputStream);
            }
        }
    }

    private static void OutputCacheResponse(HttpContext context, DateTime lastModified) {
        HttpCachePolicy cachePolicy = context.Response.Cache;
        cachePolicy.SetCacheability(HttpCacheability.Public);
        cachePolicy.VaryByParams["p"] = true;
        cachePolicy.SetOmitVaryStar(true);
        cachePolicy.SetExpires(DateTime.Now + TimeSpan.FromDays(365));
        cachePolicy.SetValidUntilExpires(true);
        cachePolicy.SetLastModified(lastModified);
    }

    public bool IsReusable {
        get {
            return true;
        }
    }
}

当我尝试物理或通过代码删除图片文件时，出现“无法访问文件，正在被另一个进程使用”错误。

这是由缩略图缓存引起的吗或者文件是否在我无法发现的地方被关闭？

是否是我的上传文件脚本导致的？

Answer 1

您似乎没有在任何地方关闭 MemoryStream ？仅靠垃圾收集并不能消除文件锁，不是吗？在 ProcessRequest 末尾添加一个 memoryStream.Close() 不会有什么坏处。