Question

I need an advice on multithreading implementation in WinForms C# application. We have an image – with text and numbers and there are separate methods to OCR different types of data. For example:

decimal[] numbers = getNumbers(bitmap, dictionary1);
string[] text = getText(bitmap, dictionary2);
int[] integers = getInts(bitmap, dictionary3);
// add 5 more data types (list, int[], etc..)

As the result, whole proccess takes approximately 1 second.

I was thinking about running OCR on different threads, simultaneously. For that reason I tried to use Task Factory:

decimal[] numbers;
Task.Factory.StartNew(() =>
{numbers = getNumbers(bitmap, dictionary1);});
string[] text;
Task.Factory.StartNew(() =>
{text = getText(bitmap, dictionary2);});
textBox1.Text = "" + text[0]; // nothing

but I was not getting any results..

so is it possible to implemet multithreading in my case? Which approach do I have to use?

• task factory
• background worker
• threads
• or something else?

If possible, can you give me a little advice on how to use your method, because TaskFactory failed when I tried to use it (as in example).

Edit:

seems like

textBox1.Text = "" + text[0];

was executed faster than

string[] text;
Task.Factory.StartNew(() =>
{text = getText(bitmap, dictionary2);});

that’s why TextBox field was empty.. so I moved “textBox1.Text = “” + text[0];” at the very end of the code, and finally got the result..

Edit 2:

ok, tasks do not make any difference.. I’m getting the same speed test result without them.

Answer 1

You’re starting tasks correctly, but you’re never waiting for them to finish. What you want to do is something similar to;

Task[] tasks = new Task[2];
decimal[] numbers;
tasks[0] = Task.Factory.StartNew(() =>
   {numbers = getNumbers(bitmap, dictionary1);});
string[] text;
tasks[1] = Task.Factory.StartNew(() =>
   {text = getText(bitmap, dictionary2);});

Task.WaitAll(tasks);  // Wait for all parallel tasks to finish 
                      // before using their output.

textBox1.Text = "" + text[0];

More example code can be found here.

Alternately, you can return the value from the task instead of assigning it to a variable and use Task.Result which when you access it will wait for the task to finish and return the result of the Task.