Nopcommerce 使用Task时dbcontext关闭问题

1、开启一个线程

Task.Run(() => { CreatPrintImage(preViewModel.DiyProductGuid); });

2、线程代码

        /// <summary>
        /// 生成打印图片 (这里一定要异步，开另外一个线程调用，不用接受返回)
        /// </summary>
        /// <param name="diyGuid"></param>
        /// <returns></returns>
        public void CreatPrintImage(string  diyGuid)
        {
            lock (obj)
            {
                using (var lifeTime = EngineContext.Current.ContainerManager.Container.BeginLifetimeScope())
                {
                    var productService = lifeTime.Resolve<IProductService>();
                    var pictureService = lifeTime.Resolve<IPictureService>();
                    var downloadService = lifeTime.Resolve<IDownloadService>();
                    var product = productService.GetProdcutByDiyGuid(diyGuid);
                    //var product = _productService.GetProductById(productId);
                    var diyItem = product.DiyItem;
                    var diyItemTemplate = diyItem.DiyItemTemplates.FirstOrDefault();
                    foreach (var pp in product.ProductPictures)
                    {
                        #region 合成打印图片
                        double bitmapWidth = 0;
                        double bitmapHeight = 0;
                        if (diyItemTemplate != null)
                        {
                            //如果是盒子
                            if (diyItem.DiyType.IdentNumber == "10005")
                            {
                                switch (pp.DiyItemTemplateName)
                                {
                                    case "上":
                                        bitmapWidth = diyItemTemplate.EditWidth;
                                        bitmapHeight = diyItemTemplate.EditHeight;
                                        break;
                                    case "下":
                                        bitmapWidth = diyItemTemplate.EditWidth;
                                        bitmapHeight = diyItemTemplate.EditHeight;
                                        break;
                                    case "左":
                                        bitmapWidth = diyItemTemplate.EditHeight;
                                        bitmapHeight = diyItemTemplate.EditLong ?? 0;
                                        break;
                                    case "右":
                                        bitmapWidth = diyItemTemplate.EditHeight;
                                        bitmapHeight = diyItemTemplate.EditLong ?? 0;
                                        break;
                                    case "中":
                                        bitmapWidth = diyItemTemplate.EditWidth;
                                        bitmapHeight = diyItemTemplate.EditLong ?? 0;
                                        break;
                                }
                            }
                            else
                            {
                                bitmapWidth = diyItemTemplate.EditWidth;
                                bitmapHeight = diyItemTemplate.EditHeight;
                            }
                            var bitmap = new Bitmap((int)bitmapWidth, (int)bitmapHeight);
                            var huabug = Graphics.FromImage(bitmap);
                            foreach (var sideItem in pp.DiyInfoSideItems.OrderBy(s => s.DisplayOrder))
                            {
                                var printDiyInfo = new PrintDiyInfo();
                                printDiyInfo.RotationAngle = sideItem.DiyInfoRotate;
                                printDiyInfo.CenterMarginLeft = sideItem.CenterMarginLeft ?? 0;
                                printDiyInfo.CenterMarginTop = sideItem.CenterMarginTop ?? 0;
                                printDiyInfo.TemplateZoom = pp.ShowScaling ?? 0;
                                printDiyInfo.EditWidth = 0;
                                printDiyInfo.EditHeight = 0;
                                //如果是盒子
                                if (diyItem.DiyType.IdentNumber == "10005")
                                {
                                    switch (pp.DiyItemTemplateName)
                                    {
                                        case "上":
                                            printDiyInfo.RotationAngle = 180;
                                            break;
                                        case "下":
                                            printDiyInfo.RotationAngle = 0;
                                            break;
                                        case "左":
                                            printDiyInfo.RotationAngle = 90;
                                            break;
                                        case "右":
                                            printDiyInfo.RotationAngle = 270;
                                            break;
                                    }
                                }
                                //如果是图片或者是贴纸
                                if (sideItem.DiyInfoType == DiyInfoTypeEnum.Picture ||
                                    sideItem.DiyInfoType == DiyInfoTypeEnum.Paster)
                                {
                                    string originalPictureUrl = sideItem.DiyInfoType == DiyInfoTypeEnum.Picture ? pictureService.GetPictureUrl(sideItem.PictureId ?? 0) : pictureService.GetPictureUrl(sideItem.PasterId ?? 0);
                                    var mapPath = _webHelper.MapPath(originalPictureUrl.Substring(originalPictureUrl.IndexOf("/Content", StringComparison.Ordinal)));
                                    var bit = new Bitmap(mapPath);
                                    //缩放
                                    var bm1 = new Bitmap(bit, Convert.ToInt32(bit.Width * printDiyInfo.TemplateZoom * sideItem.DiyInfoZoom), Convert.ToInt32(bit.Height * printDiyInfo.TemplateZoom * sideItem.DiyInfoZoom));
                                    var ms = new MemoryStream();
                                    bm1.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
                                    byte[] bytes = ms.GetBuffer();
                                    //旋转
                                    var imageFactory = new ImageFactory();
                                    imageFactory.Load(bytes);
                                    imageFactory.Rotate((float)printDiyInfo.RotationAngle);
                                    var rotationImage = imageFactory.Image;
                                    if (rotationImage != null)
                                    {
                                        var pointx = Convert.ToInt32(printDiyInfo.CenterMarginLeft * printDiyInfo.TemplateZoom - rotationImage.Width / 2);
                                        var pointy = Convert.ToInt32(printDiyInfo.CenterMarginTop * printDiyInfo.TemplateZoom - rotationImage.Height / 2);
                                        var ulCorner = new Point(pointx, pointy);
                                        huabug.DrawImage(rotationImage, ulCorner);
                                    }
                                }
                                else if (sideItem.DiyInfoType == DiyInfoTypeEnum.Font)
                                {
                                    var sidefont = downloadService.GetDownloadById(sideItem.FontId ?? 0);
                                    if (sidefont != null)
                                    {
                                        var fontUrl = _webHelper.MapPath(sidefont.DownloadUrl);
                                        var frm = new PrivateFontCollection();
                                        frm.AddFontFile(fontUrl);
                                        var fontFamily = frm.Families[0];
                                        var fontSize = 51 * (float)sideItem.DiyInfoZoom;
                                        var fontColor = ColorTranslator.FromHtml(sideItem.FontColor);
                                        var fontStyle = new FontStyle();
                                        if ((sideItem.FontIsBold ?? false) && (sideItem.FontIsItalic ?? false))
                                        {
                                            fontStyle = FontStyle.Bold | FontStyle.Italic;
                                        }
                                        else if ((sideItem.FontIsBold ?? false))
                                        {
                                            fontStyle = FontStyle.Bold;
                                        }
                                        else if (sideItem.FontIsItalic ?? false)
                                        {
                                            fontStyle = FontStyle.Italic;
                                        }
                                        var font = new Font(fontFamily, fontSize, fontStyle);
                                        //定义颜色
                                        var sbrush = new SolidBrush(fontColor);
                                        // 绘制围绕点旋转的文本
                                        var pointx = Convert.ToInt32(printDiyInfo.CenterMarginLeft * printDiyInfo.TemplateZoom);
                                        var pointy = Convert.ToInt32(printDiyInfo.CenterMarginTop * printDiyInfo.TemplateZoom);
                                        var point = new PointF(pointx, pointy);
                                        //var point = new PointF(200, 200);
                                        StringFormat format = new StringFormat();
                                        format.Alignment = StringAlignment.Center;
                                        format.LineAlignment = StringAlignment.Center;
                                        Matrix mtxRotate = huabug.Transform;
                                        mtxRotate.RotateAt((float)printDiyInfo.RotationAngle, point); // 旋转角度和平移
                                        huabug.Transform = mtxRotate;
                                        huabug.DrawString(sideItem.FontString, font, sbrush, point, format);
                                    }
                                }
                            }
                            string printMapPath = _webHelper.MapPath(_filePath);
                            if (!System.IO.Directory.Exists(printMapPath))
                            {
                                System.IO.Directory.CreateDirectory(printMapPath);
                            }
                            var printFileName = pp.DiyItemTemplateName + "diy_" + Guid.NewGuid().ToString().ToLower().Replace("-", "") + ".png";
                            var printPicUrl = "/Content/Uploads/Images/PrintImage/" + DateTime.Now.ToString("yyyyMM") + "/" + printFileName;
                            bitmap.Save(_webHelper.MapPath(printPicUrl));
                            pp.PrintImageUrl = printPicUrl;
                            #endregion
                            //productPictureService.UpdateProductPicture(pp);
                        }
                    }
                    productService.UpdateProduct(product);
                }
            } 
        }