object is currently in use elsewhere

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hello every body,
i have a small project, in which i am using Two Threads, and a method to draw circle on an image. when it starts so after some time it gives the error message object is currently in use elsewhere. sample of code is been give blow please, if anyone could give me some guidelines or some idea please.

C#

 private delegate void DrawCircleDelegate(Point pp, Bitmap r);
        public void DrawCircle(Point p, Bitmap rate)
        {
            if (InvokeRequired)
            {
                DrawCircleDelegate drwCircle = new DrawCircleDelegate((pp,r)=> DrawCircle(p,rate));
                this.BeginInvoke(drwCircle, new object[] { p,rate });
            }
            // utilObject.StateOccure += new SimUtil.InvalidState(utilObject_StateOccure); // Event handler , to handle invalid states
            Bitmap tempbitmap = (Bitmap)testImage.Clone();
            Graphics g = Graphics.FromImage(tempbitmap);

            if (rate== null )
                g.FillEllipse(Brushes.Green, p.X - 15, p.Y - 15, 30, 30);            
            else 
                g.DrawImage(rate, p.X - 15, p.Y - 15, 30, 30);

            pictureBox1.Image = tempbitmap;

        }
private void frmTwoThreads_Load(object sender, EventArgs e)
        {
            testImage = new Bitmap(@"D:\Practice_Projects\TestPic.png");
            rnd = new Random(DateTime.Now.Second);
            findNextThread = new Thread(FindNext);
            findNextThread.Name = " Find Thread";

        }
private void btnStarSimulator_Click(object sender, EventArgs e)
        {
            utilObject = new SimUtil();
            //rnd = new Random(DateTime.Now.Second);
           // List<Cell> gridCell = new List<Cell>();
            myGrid = new Grid(row, col, new Point(10, 10), new Point(460, 440));

            for (int clNo = 1; clNo <= myGrid.TotalCells; clNo++)
            {
                Cell tempCell = new Cell(clNo, col, row, myGrid.InitialPoint, myGrid.GridSize);
                myGrid.Cells.Add(tempCell);
            }
            testImage = myGrid.DrawGridOnBitmap(testImage, myGrid.InitialPoint, myGrid.EndPoint);
            pictureBox1.Image = testImage;
            DrawCircle(Get_CellCenterPoint(startCell),null);          


            findNextThread.Start();
        }
  public void FindNext()
        {

            while (true)
            {

                //moveCircleDelegate mcircle = moveCircle;               
                Point fromCellPoint;
                Point toCellPoint;
                int nextLocation = utilObject.SelectNextCell(startCell, rnd);
                while (nextLocation  <= 0 || nextLocation  > 100)
                {
                    string s1 = startCell.ToString() + " , " + nextLocation.ToString();
                    this.Invoke((MethodInvoker)delegate { listBox1.Items.Add(s1); });  
                    nextLocation = utilObject.SelectNextCell(startCell, rnd);
                }
                              
                    fromCellPoint = Get_CellCenterPoint(startCell);
                    toCellPoint = Get_CellCenterPoint(nextLocation);
                    string s = startCell.ToString() + " , " + nextLocation.ToString() ;
                    this.Invoke((MethodInvoker)delegate { listBox1.Items.Add(s); });             
                     moveCircleThread = new Thread(() => moveCircle(fromCellPoint, toCellPoint, 100));
                     moveCircleThread.Start();
                     moveCircleThread.Join();
                     startCell = nextLocation;
            }
        }

Posted 28-Nov-13 0:40am

Muhammad Tufail 1979

Updated 13-Jan-22 3:11am

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Comments

agent_kruger 28-Nov-13 6:50am

in which line do you recieve the error?

Muhammad Tufail 1979 28-Nov-13 6:54am

thank you so much on your reply,
in the method DrawCircle, i am running this at the moment on my computer and i got again this error, it is exactly at
Bitmap tempbitmap = (Bitmap)testImage.clone();
while previously i got at
g.DrawImage( rate,p.x-15,p.y-15,30,30);
thanks once again

3 solutions

Solution 1

try using

Bitmap tempbitmap = (Bitmap)testImage;

Posted 28-Nov-13 1:01am

agent_kruger

Comments

Muhammad Tufail 1979 28-Nov-13 7:03am

okay thank you i am going toward it now. some time id does not give error even for long long time, while some time gives error after short time of starting .
i don't know whats the problem.

Muhammad Tufail 1979 28-Nov-13 7:07am

okay i did apply the above, now as i run the project so at the same time i am getting that error

Muhammad Tufail 1979 28-Nov-13 7:14am

i never got this error when i was running this program on my office machine. but when i run it at my laptop so it give me this error

Solution 3

To avoid multiple threads accessing an image object I recommend always cloning the image and make sure each thread is working with its own clone.

Thread1_Img = MasterImage.Clone
Thread2_Img = MasterImage.Clone

This way each image is independent. This approach uses more memory, but is a safe way to work with images in a multi-threaded environment.

You should make sure you are cloning the image before handing it off to any new threads - otherwise it's too late. You cannot safely clone an image once another thread begins using it.

Posted 12-Mar-21 5:43am

Dan Desjardins

Updated 12-Mar-21 5:45am

v2

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Dmytro Bogachev · Accepted Answer · 2013-11-28T01:25:00

Images in GDI+ are not thread safe. What it means, basically - you cannot use one image from 2 threads simultaneously without some additional changes to your code.
Look at following pseudo code:

C#

public void SetPixels()
{
    var bmp = new Bitmap("Some image"); //Omitted using(), which is often mandatory
    var t = new Task(() => { for (int i = 0; i < 1000000; i++) {  
        bmp.SetPixel(0, 1, Color.Black); } });
    var t2 = new Task(() => { for (int i = 0; i < 1000000; i++) { 
        bmp.SetPixel(0, 1, Color.Black); } });
    t.Start();
    t2.Start();
    //Omitted wait for completion
}

At some moment here you will have "InvalidOperationException", which you described, since 2 different threads are setting colors of pixel in one image at same time.
You have to make lock each time, before you accessing to you bitmap.
On class level, declare variable

C#

private object _locker = new object();

And, in pseudo code, similar construction, as above, but which will execute without exceptions:

C#

public void SetPixels()
{
    var bmp = new Bitmap("Some image"); //Omitted using(), which is often mandatory
    var t = new Task(() => { for (int i = 0; i < 1000000; i++) 
        { lock (_locker) { bmp.SetPixel(0, 1, Color.Black); } } });
    var t2 = new Task(() => { for (int i = 0; i < 1000000; i++) 
        { lock (_locker) { bmp.SetPixel(0, 1, Color.Black); } } });
    t.Start();
    t2.Start();
    //Omitted wait for completion
}

lock is built-in C# language construction; you can find info about it on MSDN.