How to create and start new Task

private void LongTaskNoParam()
{
// do something here
}

Task task1 = new Task(LongTaskNoParam);
task1.Start();

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How to create and start new Task with factory

Task task2 = Task.Factory.StartNew(LongTaskNoParam);

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How to pass parametr to a Task

private void LongTaskParam(object myParam)
{
// do something here
}

Task task3 = Task.Factory.StartNew(LongTaskParam, 3000);

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How to wait for a Task

task3.Wait();

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How to run task synchronously on the same thread

Task task4 = new Task(LongTaskNoParam);
task4.RunSynchronously();

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Run async, return a value and wait for completion

public async Task<string> RunsAsynchronously(int sleepTime)
{
  Log("1");
  await Task.Delay(sleepTime);
  Log("2"); // start + sleep time
  return " Finished Async";
}

private async void button1_Click(object sender, EventArgs e)
{
  string s = await RunsAsynchronously(3000);
  Log("3"); // start + sleep time
}

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What will happen when async worker method is not called with await

public async Task<string> RunsAsynchronously(int sleepTime)
{
  Log("2");
  await Task.Delay(sleepTime);
  Log("3");
  return " Finished Async";
}

private async void button1_Click(object sender, EventArgs e)
{
  RunsAsynchronously(3000); // cannot assign result "string s = " without "await"
  Log("1"); // start RunsAsynchronously() and continues
}

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What will happen when async worker method is called with await, but worker code does not await

public async Task<string> RunsAsynchronously(int sleepTime)
{
  Log("1");
  Task.Delay(sleepTime); // will not wait here without "await"
  Log("2"); // Log("1") + 0.01sec
  return " Finished Async";
}

private async void button1_Click(object sender, EventArgs e)
{
  string s = await RunsAsynchronously(3000);
  Log("3"); // Log("2") + 0.01s time
}

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When method with async signature will not run asynchronously

public async Task<string> WillNotRunAsync()
{
Thread.Sleep(2000); // simulates long running method
return "Did not run async";
}

Task<string> result = await WillNotRunAsync();

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How to call a method without async signature asynchronously from an async method

private string LongTaskWithResult()
{
  Thread.Sleep(5000);
  return "LongTaskWithResult";
}

private async Task<string> LongTaskWithResultAsync()
{
  string s = await Task.Factory.StartNew(() => LongTaskWithResult());
  return s;
}
...

string s = await LongTaskWithResultAsync();

or call it directly, if the caller is marked as async

string s = await Task.Factory.StartNew(() => LongTaskWithResult());

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How to call a method with async signature asynchronously from a non async method

string s;
Task.Factory.StartNew(async () =>
{
  s = await LongTaskWithResultAsync();
  // here the code waits
  DoSomething();
});
// here the code does NOT wait

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How to update UI from non UI thread

using System.Threading;
....

SynchronizationContext m_syncContext;
SendOrPostCallback m_UIUpdateMethod;

public MyForm()
{
  m_syncContext = SynchronizationContext.Current; // stores main thread context
  m_UIUpdateMethod = UIUpdateMethod;
}

private void UIUpdateMethod(object state)
{
textBox1.Text += (string)state;
}

public async Task MyAsynchronousMethod()
{
  m_syncContext.Post(m_UIUpdateMethod, "Hello from MyAsynchronousMethod()");
}

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How to cancel an async call

private void LongTask(CancellationToken ct)
{
  for (int i=0; i < 100; i++)
  {
    if (ct.IsCancellationRequested)
    {
      return;
    }
    else
    {
      // Do something
    }
  }
}

CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken ct = cts.Token;
Task.Factory.StartNew(() => LongTask(ct), ct);

...
cts.Cancel(); // cancel when needed

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