I have a task and I expect it to take under a second to run but if it takes longer than a few seconds I want to cancel the task.
For example:
Task
If you want to cancel a Task
, you should pass in a CancellationToken
when you create the task. That will allow you to cancel the Task
from the outside. You could tie cancellation to a timer if you want.
To create a Task with a Cancellation token see this example:
var tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;
var t = Task.Factory.StartNew(() => {
// do some work
if (token.IsCancellationRequested) {
// Clean up as needed here ....
}
token.ThrowIfCancellationRequested();
}, token);
To cancel the Task
call Cancel()
on the tokenSource
.
Was the task canceled when the timeout expired or is the task still running?
No and Yes.
The timeout passed to Task.Wait
is for the Wait
, not the task.
The task is still running until you explicitly tell it to stop or your loop finishes (which will never happen).
You can check the return value of Wait to see this:
(from http://msdn.microsoft.com/en-us/library/dd235606.aspx) Return Value
Type: System.Boolean true if the Task completed execution within the allotted time; otherwise, false.
If your task calls any synchronous method that does any kind of I/O or other unspecified action that takes time, then there is no general way to "cancel" it.
Depending on how you try to "cancel" it, one of the following may happen:
There are valid scenarios where you can and probably should cancel a task using one of the generic methods described in the other answers. But if you are here because you want to interrupt a specific synchronous method, better see the documentation of that method to find out if there is a way to interrupt it, if it has a "timeout" parameter, or if there is an interruptible variation of it.
Task.Wait()
waits up to specified period for task completion and returns whether the task completed in the specified amount of time (or earlier) or not. The task itself is not modified and does not rely on waiting.
Read nice series: Parallelism in .NET, Parallelism in .NET – Part 10, Cancellation in PLINQ and the Parallel class by Reed Copsey
And: .NET 4 Cancellation Framework / Parallel Programming: Task Cancellation
Check following code:
var cts = new CancellationTokenSource();
var newTask = Task.Factory.StartNew(state =>
{
var token = (CancellationToken)state;
while (!token.IsCancellationRequested)
{
}
token.ThrowIfCancellationRequested();
}, cts.Token, cts.Token);
if (!newTask.Wait(3000, cts.Token)) cts.Cancel();