Please help Parallel.ForEach is not working with graphics

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C#

System.Threading.Tasks.Parallel.ForEach(ktl,rc=>
                           {
                               ++i;

                               g.DrawRectangle(pen, rc);

                               g.DrawString("KN" + i.ToString(), new Font(FontFamily.GenericSansSerif, 10, FontStyle.Bold),
                      new SolidBrush(Color.Blue), rc.X, rc.Y);
                           }
                       );

but this works

C#

foreach (Rectangle rc in ktl)
                    {

                        ++i;
                        g.DrawRectangle(pen, rc);

                        g.DrawString("KN"+i.ToString(), new Font(FontFamily.GenericSansSerif, 10, FontStyle.Bold),
               new SolidBrush(Color.Blue), rc.X, rc.Y);

                    }

Posted 28-May-15 20:26pm

vishnulalr

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Sascha Lefèvre · Answer 1 · 2015-05-28T21:07:00

At the bottom of the MSDN-page for the Graphics[^]-class they state:

"Any public static members of this type are thread safe. Any instance members are not guaranteed to be thread safe."

Sidenote: Any object of a class that implements IDisposable should be disposed after use, which can be easiest achieved by using it within a using-block. You should do this with your Font and Solidbrush. As it's always the same Font and SolidBrush, there's no need to allocate a new one in each iteration of your loop anyway.