Error "Object is currently in use elsewhere."

Question

Hi!
I am trying to use "Task", but I got Error "Object is currently in use elsewhere."
Bitmap oriBitmap = new Bitmap(pictureBox1.Image);
Task[] tasks = new Task[4];
for (int k = 1; k <= tasks.Length; k++)
int count = k;
tasks[k] = Task.Factory.StartNew(() =>
int minJ = count < 2 ? 0 : oriBitmap.Height / 2;
int maxJ = count < 2 ? oriBitmap.Height / 2 : oriBitmap.Height;
int minI = count % 2 == 0 ? 0 : oriBitmap.Width / 2;
int maxI = count % 2 == 0 ? oriBitmap.Width / 2 : oriBitmap.Width;
for (int j = minJ; j < maxJ; j += 8)
for (int i = minI; i < maxI; i += 8)
if (((i + 68) < oriBitmap.Width) && ((j + 68) < oriBitmap.Height))
Bitmap bmp = new Bitmap(68, 68);
//Get Clone 68 x 68
using (var g = Graphics.FromImage(bmp))
g.DrawImage(oriBitmap, new Rectangle(0, 0, 68, 68), new Rectangle(i, j, 68, 68), GraphicsUnit.Pixel);
//Process Clone
I've tried to fix it but sometimes I got Error in line
if (((i + 68) < oriBitmap.Width) && ((j + 68) < oriBitmap.Height))
and
g.DrawImage(oriBitmap, new Rectangle(0, 0, 68, 68), new Rectangle(i, j, 68, 68), GraphicsUnit.Pixel);
Is there any idea to fix it?
Thanks,.

Answer 1

Hi,
if you just read the Bitmap from multiple threads, it *may* help to put the Width and Height into separate Variables before the threads are spawned. Something like int w = oriBitmap.Width, same for height, then start the tasks and access the w and h variables
from the threads. This is a common technique when using a Parallel.For etc.
But since you draw the Bitmap in the threads, Vidya Vrat Agarwal's reply will be the correct one.
What you could do, is to copy the parts of the bitmap, that are processed in each task before creating the tasks. So, if you create 4 tasks, get 4 threadlocal Bitmap-copies that contain the part of the orig Bitmap to be processed.
Regards,
  Thorsten