I have the following problem:
I need to run a function search (depth x) that basically searches a decision tree until a certain depth and then returns (or leaves in a class member) a value of type Move. At the same time I would like to be able to "cancel" the execution of the search if it goes on for too long.
It is also important that I don't have to wait for it if the search does finish faster. I realize this is not a complicated but I am not really familiar with C# concurrency controls.
Here is a simple example as starting point:
public class Runner
{
private Task<int> search(CancellationToken ct)
{
var t_work = Task.Factory.StartNew<int>(() =>
{
int k = 0;
while (k < 1000)
{
if (ct.IsCancellationRequested)
{
return -1;
}
k += r.Next(200);
Thread.Sleep(300);
}
return k;
}, ct);
return t_work;
}
Random r = new Random();
public async Task SearchAsync()
{
var timeout = TimeSpan.FromSeconds(3);
var cts = new CancellationTokenSource(timeout);
var ct = cts.Token;
var searchValue = await search(ct);
string result = (searchValue < 0) ?
"Search aborted without results" : "search value is: " + searchValue.ToString();
Console.WriteLine(result);
}
}
you can use it in a console app like this:
Console.WriteLine("test");
var r = new Runner();
r.SearchAsync().Wait();
r.SearchAsync().Wait();
r.SearchAsync().Wait();
r.SearchAsync().Wait();
Console.WriteLine("done..");
I would use a Task for this, as it has built in mechanisms to handle errors, cancellation, and running Continuation Tasks when the task completes.
Assuming a custom return type of Move which I think you implied in your question:
private Task<Move> _searchTask;
private CancellationTokenSource _searchCancellationTokenSrc;
Then on a button click or similar, kick off your task. This will return immediately, keeping your UI responsive:
private void StartButton_Click(object sender, RoutedEventArgs e)
{
_searchCancellationTokenSrc = new CancellationTokenSource();
CancellationToken ct = _searchCancellationTokenSrc.Token;
_searchTask = Task.Run(() =>
{
for (int i = 0; i < 10; i++ )
{
if(ct.IsCancellationRequested)
{
// Clean up here
ct.ThrowIfCancellationRequested();
}
// Time consuming processing here
Thread.Sleep(1000);
}
return new Move();
},ct);
_searchTask.ContinueWith((t) =>
{
Console.WriteLine("Canceled");
}, TaskContinuationOptions.OnlyOnCanceled);
_searchTask.ContinueWith((t) =>
{
Console.WriteLine("Faulted. t.Exception contains details of any exceptions thrown");
}, TaskContinuationOptions.OnlyOnFaulted);
_searchTask.ContinueWith((t) =>
{
Console.WriteLine("Completed t.Result contains your Move object");
}, TaskContinuationOptions.OnlyOnRanToCompletion);
}
To cancel this, perhaps from another button:
private void CancelButton_Click(object sender, RoutedEventArgs e)
{
_searchCancellationTokenSrc.Cancel();
}
backgroundworkerandTaskasync implementations support cancellation (though by different approaches, one bybooland other bytoken). I suggest usingTaskas it is a newer approach.