调整图像大小的异步任务

Question

This is my image resizer class:

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.IO;
using System.Threading.Tasks;
public class ImageResize
{
    private static ImageCodecInfo jpgEncoder;
    public async static void ResizeImage(string inFile, string outFile,
    double maxDimension, long level)
    {
        byte[] buffer;
        using (Stream stream = new FileStream(inFile, FileMode.Open))
        {
            buffer = new byte[stream.Length];
            await Task<int>.Factory.FromAsync(stream.BeginRead, stream.EndRead,
            buffer, 0, buffer.Length, null);
        }
        using (MemoryStream memStream = new MemoryStream(buffer))
        {
            using (Image inImage = Image.FromStream(memStream))
            {

                double width;
                double height;
                if (inImage.Height < inImage.Width)
                {
                    width = maxDimension;
                    height = (maxDimension / (double)inImage.Width) * inImage.Height;
                }
                else
                {
                    height = maxDimension;
                    width = (maxDimension / (double)inImage.Height) * inImage.Width;
                }
                using (Bitmap bitmap = new Bitmap((int)width, (int)height))
                {
                    using (Graphics graphics = Graphics.FromImage(bitmap))
                    {

                        graphics.SmoothingMode = SmoothingMode.HighQuality;
                        graphics.InterpolationMode =
                        InterpolationMode.HighQualityBicubic;
                        graphics.DrawImage(inImage, 0, 0, bitmap.Width, bitmap.Height);

                        if (inImage.RawFormat.Guid == ImageFormat.Jpeg.Guid)
                        {
                            if (jpgEncoder == null)
                            {
                                ImageCodecInfo[] ici =
                                ImageCodecInfo.GetImageDecoders();
                                foreach (ImageCodecInfo info in ici)
                                {
                                    if (info.FormatID == ImageFormat.Jpeg.Guid)
                                    {
                                        jpgEncoder = info;
                                        break;
                                    }
                                }
                            }
                            if (jpgEncoder != null)
                            {
                                EncoderParameters ep = new EncoderParameters(1);
                                ep.Param[0] = new EncoderParameter(Encoder.Quality,
                                level);
                                bitmap.Save(outFile, jpgEncoder, ep);
                            }
                            else
                                bitmap.Save(outFile, inImage.RawFormat);
                        }
                        else
                        {
                            //
                            // Fill with white for transparent GIFs
                            //
                            graphics.FillRectangle(Brushes.White, 0, 0, bitmap.Width,
                            bitmap.Height);
                            bitmap.Save(outFile, inImage.RawFormat);
                        }
                    }
                }
            }
        }
    }
}

And this is my register button server click:

    HttpPostedFile file = Request.Files["ctl00$cph$postFile"];
    string FileName = "";

    if (file.ContentLength > 0)
    {
        string[] ValidExt = { ".jpg", ".jpeg" };

        string fileExt = Path.GetExtension(file.FileName).ToLower();

        if (Array.IndexOf(ValidExt, fileExt) < 0)
        {
            return;
        }
        if (file.ContentLength / 1024 > 5120)
        {
            return;
        }
        string path = Server.MapPath("~/upload/image_upload/ads/");
        string[] s = file.FileName.Split('\\');

        FileName = System.IO.Path.GetFileName(s[s.Length - 1]);
        while (System.IO.File.Exists(path + FileName))
        {
            Random r = new Random();
            int rn = (DateTime.Now + r.Next().ToString()).GetHashCode();
            FileName = rn + " " + FileName;
        }
        string FullPath = path + FileName;
        file.SaveAs(FullPath);
        ImageResize.ResizeImage(FullPath, FullPath, 800, 80);
        string thPath = path + "th\\" + FileName;
        file.SaveAs(thPath);
        ImageResize.ResizeImage(thPath, thPath, 300, 90);

    }
    SqlConnection con = new SqlConnection(cs);

    StringBuilder sb = new StringBuilder();
    sb.Append("BEGIN TRY BEGIN TRANSACTION");
    sb.Append(" declare @result bit=0; declare @ad_id int;");
    sb.Append("INSERT INTO tbl_ads(ad_title,ad_brief,ad_text,ad_pic,ad_datesave,ad_is_accept,ad_is_show,ad_visit,ad_type,ad_user,ad_is_slide)");
    sb.Append(" VALUES(@ad_title,@ad_brief,@ad_text,@ad_pic,@ad_datesave,@ad_is_accept,@ad_is_show,@ad_visit,@ad_type,@ad_user,@ad_is_slide);");
    sb.Append("set @ad_id=SCOPE_IDENTITY();");

    SqlCommand cmd = new SqlCommand();
    cmd.Connection = con;

    cmd.Parameters.AddWithValue("@ad_title", txt_title.Value);
    cmd.Parameters.AddWithValue("@ad_brief", txt_brief.Value);
    cmd.Parameters.AddWithValue("@ad_text", txt_full.Value);
    cmd.Parameters.AddWithValue("@ad_pic", FileName);
    cmd.Parameters.AddWithValue("@ad_datesave", PersianDate.GetDate(0));
    cmd.Parameters.AddWithValue("@ad_is_accept", chk_accept.Checked);
    cmd.Parameters.AddWithValue("@ad_is_show", chk_show.Checked);
    cmd.Parameters.AddWithValue("@ad_visit", 0);
    cmd.Parameters.AddWithValue("@ad_type", lst_type.Value);
    cmd.Parameters.AddWithValue("@ad_user", -1*(int)Session["u_id"]);
    cmd.Parameters.AddWithValue("@ad_is_slide", chk_slide.Checked);


    string[] SubcatIds = inp_subcats.Value.Split(',');
    string[] StateIds = inp_states.Value.Split(',');
    string[] CityIds = inp_cities.Value.Split(',');


    if (CatIds[0] != "")
    {
        for (int i = 0; i < CatIds.Length; i++)
        {
            cmd.Parameters.AddWithValue("@cat_id" + i, CatIds[i]);
            sb.Append("INSERT INTO tbl_inf_adcat(ad_id,cat_id) VALUES(@ad_id,@cat_id" + i + ");");
        }
    }

    if (SubcatIds[0] != "")
    {
        for (int i = 0; i < SubcatIds.Length; i++)
        {
            cmd.Parameters.AddWithValue("@subcat_id" + i, SubcatIds[i]);
            sb.Append("INSERT INTO tbl_inf_adsubcat(ad_id,subcat_id) VALUES(@ad_id,@subcat_id" + i + ");");
        }
    }

    if (StateIds[0] != "")
    {
        for (int i = 0; i < StateIds.Length; i++)
        {
            cmd.Parameters.AddWithValue("@state_id" + i, StateIds[i]);
            sb.Append("INSERT INTO tbl_inf_adstate(ad_id,state_id) VALUES(@ad_id,@state_id" + i + ");");
        }
    }

    if (CityIds[0] != "")
    {
        for (int i = 0; i < CityIds.Length; i++)
        {
            cmd.Parameters.AddWithValue("@city_id" + i, CityIds[i]);
            sb.Append("INSERT INTO tbl_inf_adcity(ad_id,city_id) VALUES(@ad_id,@city_id" + i + ");");
        }
    }


    sb.Append("COMMIT set @result=1 select @result  END TRY BEGIN CATCH IF @@TRANCOUNT > 0 ROLLBACK select  @result END CATCH");

    cmd.CommandText = sb.ToString();

    try
    {

        con.Open();

        bool result = Convert.ToBoolean(cmd.ExecuteScalar());

        if (result == true)
        {
            ClientAlert.modalBoxInfo(this, "success");

        }
        else
        {
            ClientAlert.modalBoxAlert(this, "error");
        }

    }
    catch
    {
        ClientAlert.modalBoxAlert(this, "error");
    }
    finally
    {
        con.Close();
    }

}

But when I want to run this method an error occur :

An asynchronous module or handler completed while an asynchronous operation was still pending.

I used Async="true" in the page directive and I test it in visual studio but in the real host it has that error. Is it because I used a transaction? Advance Regards.

Answer 1

No, it's because of the

await Task<int>.Factory.FromAsync(stream.BeginRead, stream.EndRead,
        buffer, 0, buffer.Length, null);

The tricky part is that your async method is returning void . That's a big no-no unless you know what you're doing (which you obviously don't right now). Have it return Task instead, and the same for all the other callers all the way to the request handler itself. That will allow you to marshal the awaited callback back to the original request thread - otherwise, the request will simply end, causing the callback to work on an already completed request.

For await code to work correctly, you need to have this unbroken chain of Task -returning methods, as simple as that. Otherwise, at some point you're just calling a void -returning method that returns immediately and then you continue on the next statement, while the background task is still running.

Or , if you want this to be a fire-and-forget action, without having the request wait for the resize to be done, you can force the await not to try marshalling back to the request thread:

await Task<int>.Factory.FromAsync(stream.BeginRead, stream.EndRead,
        buffer, 0, buffer.Length, null).ConfigureAwait(false);

Also, it's a bad idea to save the input file to a file first. You have all you need to work with the input stream directly, why would you want to save an intermediate file? It could quite easily fail on some file locking issue.

And , when using such fire-and-forget tasks, make sure you do proper error handling. Depending on .NET framework version and configuration, an unhandled exception in a non-awaited Task will kill the whole process.