I have the following test code:
void Button_Click(object sender, RoutedEventArgs e)
{
var source = new CancellationTokenSource();
var tsk1 = new Task(() => Thread1(source.Token), source.Token);
var tsk2 = new Task(() => Thread2(source.Token), source.Token);
tsk1.Start();
tsk2.Start();
source.Cancel();
try
{
Task.WaitAll(new[] {tsk1, tsk2});
}
catch (Exception ex)
{
// here exception is caught
}
}
void Thread1(CancellationToken token)
{
Thread.Sleep(2000);
// If the following line is enabled, the result is the same.
// token.ThrowIfCancellationRequested();
}
void Thread2(CancellationToken token)
{
Thread.Sleep(3000);
}
In the thread methods I don't throw any exceptions, but I get TaskCanceledException
in try-catch
block of the outer code which starts the tasks. Why this happens and what is the purpose of token.ThrowIfCancellationRequested();
in this case. I believe the exception should only be thrown if I call token.ThrowIfCancellationRequested();
in the thread method.