I have the following method:
public async Task ScrapeObjects(int page = 1)
{
try
{
while (!isObjectSearchCompleted)
{
..do calls..
}
}
catch (HttpRequestException ex)
{
Thread.Sleep(TimeSpan.FromSeconds(60));
ScrapeObjects(page);
Log.Fatal(ex, ex.Message);
}
}
I call this long running method async and I don't wait for it to finish. Thing is that an exception my occur and in that case I want to handle it. But then I want to start from where I left and with the same thread. At the current state a new thread gets used when I recursively call the method after handling the exception. I would like to keep using the same thread. Is there a way to do so? Thank you!
You probably need to move the try/catch block inside the while loop, and add a counter with the errors occurred, to bail out in case of continuous faulted attempts.
public async Task ScrapeObjects()
{
int failedCount = 0;
int page = 1;
while (!isObjectSearchCompleted)
{
try
{
//..do calls..
}
catch (HttpRequestException ex)
{
failedCount++;
if (failedCount < 3)
{
Log.Info(ex, ex.Message);
await Task.Delay(TimeSpan.FromSeconds(60));
}
else
{
Log.Fatal(ex, ex.Message);
throw; // or return;
}
}
}
}
As a side note it is generally better to await Task.Delay instead of Thread.Sleep inside asynchronous methods, to avoid blocking a thread without a reason.
One simple question before you read the long answer below:
Why you need the same thread? Are you accessing thread static / contextual data?
If yes, there will be ways to solve that easily than limiting your tasks to run on the same thread.
How to limit tasks to run on a single thread
As long as you use async calls on the default synchronization context, and as soon as the code is resumed from an await, it is possible that the thread can change after an await. This is because the default context schedules tasks to the next available thread in the thread pool. Like in the below case, before can be different from after:
public async Task ScrapeObjects(int page = 1)
{
var before = Thread.CurrentThread.ManagedThreadId;
await Task.Delay(1000);
var after = Thread.CurrentThread.ManagedThreadId;
}
The only reliable way to guarantee that your code could come back on the same thread is to schedule your async code onto a single threaded synchronization context:
class SingleThreadSynchronizationContext : SynchronizationContext
{
private readonly BlockingCollection<Action> _actions = new BlockingCollection<Action>();
private readonly Thread _theThread;
public SingleThreadSynchronizationContext()
{
_theThread = new Thread(DoWork);
_theThread.IsBackground = true;
_theThread.Start();
}
public override void Send(SendOrPostCallback d, object state)
{
// Send requires run the delegate immediately.
d(state);
}
public override void Post(SendOrPostCallback d, object state)
{
// Schedule the action by adding to blocking collection.
_actions.Add(() => d(state));
}
private void DoWork()
{
// Keep picking up actions to run from the collection.
while (!_actions.IsAddingCompleted)
{
try
{
var action = _actions.Take();
action();
}
catch (InvalidOperationException)
{
break;
}
}
}
}
And you need to schedule ScrapeObjects to the custom context:
SynchronizationContext.SetSynchronizationContext(new SingleThreadSynchronizationContext());
await Task.Factory.StartNew(
() => ScrapeObjects(),
CancellationToken.None,
TaskCreationOptions.DenyChildAttach | TaskCreationOptions.LongRunning,
TaskScheduler.FromCurrentSynchronizationContext()
).Unwrap();
By doing that, all your async code shall be scheduled to the same context, and run by the thread on that context.
However
This is typically dangerous, as you suddenly lose the ability to use the thread pool. If you block the thread, the entire async operation is blocked, meaning you will have deadlocks.
[ This question needs to be reimagined. One of my thread queues MUST run on an STA thread, and the code below does not accommodate that. In particular it seems Task<> chooses its own thread and that just is not going to work for me. ]
I have a task queue (BlockingCollection) that I'm running through on a dedicated thread. That queue receives a series of Task<> objects that it runs sequentially within that thread via a while loop.
I need a means of Cancelling that series of tasks, and a means of knowing that the tasks are all complete. I have not been able to figure out how to do this.
Here's a fragment of my queuing class. ProcessQueue is run on a separate thread from main. QueueJob calls occur on the main thread.
using Job = Tuple<Task<bool>, string>;
public class JobProcessor
{
private readonly BlockingCollection<Job> m_queue = new BlockingCollection<Job>();
volatile bool cancel_queue = false;
private bool ProcessQueue()
{
while (true)
{
if (m_queue.IsAddingCompleted)
break;
Job tuple;
if (!m_queue.TryTake(out tuple, Timeout.Infinite))
break;
var task = tuple.Item1;
var taskName = tuple.Item2;
try
{
Console.WriteLine("Task {0}::{1} starting", this.name, taskName);
task.RunSynchronously();
Console.WriteLine("Task {0}::{1} completed", this.name, taskName);
}
catch (Exception e)
{
string message = e.Message;
}
if (cancel_queue) // CANCEL BY ERASING TASKS AND NOT RUNNING.
{
while (m_queue.TryTake(out tuple))
{
}
}
} // while(true)
return true;
}
public Task<bool> QueueJob(Func<bool> input)
{
var task = new Task<bool>(input);
try
{
m_queue.Add(Tuple.Create(task, input.Method.Name));
}
catch (InvalidOperationException)
{
Task<bool> dummy = new Task<bool>(() => false);
dummy.Start();
return dummy;
}
return task;
}
Here are the functions that trouble me:
public void ClearQueue()
{
cancel_queue = true;
// wait for queue to become empty. HOW?
cancel_queue = false;
}
public void WaitForCompletion()
{
// wait for all tasks to be completed.
// not sufficient to wait for empty queue because the last task
// must also execute and finish. HOW?
}
}
Here is some usage:
class SomeClass
{
void Test()
{
JobProcessor jp = new JobProcessor();
// launch Processor loop on separate thread... code not shown.
// send a bunch of jobs via QueueJob... code not show.
// launch dialog... code not shown.
if (dialog_result == Result.Cancel)
jp.ClearQueue();
if (dialog_result == Result.Proceed)
jp.WaitForCompletion();
}
}
The idea is after the work is completed or cancelled, new work may be posted. In general though, new work may come in asynchronously. WaitForCompletion might in fact be "when all work is done, inform the user and then do other stuff", so it doesn't strictly have to be a synchronous function call like above, but I can't figure how to make these happen.
(One further complication, I expect to have several queues that interact. While I am careful to keep things parallelized in a way to prevent deadlocks, I am not confident what happens when cancellation is introduced into the mix, but this is probably beyond scope for this question.)
WaitForCompletion() sounds easy enough. Create a semaphore or event, create a task whose only action is to signal the semaphore, queue up the task, wait on the semaphore.
When the thread finishes the last 'real' task, the semaphore task will be run and so the thread that called WaitForCompletion will become ready/running:)
Would not a similar approach work for cancellation? Have a very high priority thread that you create/signal that drains the queue of all pending jobs, disposing them, queueing up the semaphore task and waiting for the 'last task done' signal?
We could abort a Thread like this:
Thread thread = new Thread(SomeMethod);
.
.
.
thread.Abort();
But can I abort a Task (in .Net 4.0) in the same way not by cancellation mechanism. I want to kill the Task immediately.
The guidance on not using a thread abort is controversial. I think there is still a place for it but in exceptional circumstance. However you should always attempt to design around it and see it as a last resort.
Example;
You have a simple windows form application that connects to a blocking synchronous web service. Within which it executes a function on the web service within a Parallel loop.
CancellationTokenSource cts = new CancellationTokenSource();
ParallelOptions po = new ParallelOptions();
po.CancellationToken = cts.Token;
po.MaxDegreeOfParallelism = System.Environment.ProcessorCount;
Parallel.ForEach(iListOfItems, po, (item, loopState) =>
{
Thread.Sleep(120000); // pretend web service call
});
Say in this example, the blocking call takes 2 mins to complete. Now I set my MaxDegreeOfParallelism to say ProcessorCount. iListOfItems has 1000 items within it to process.
The user clicks the process button and the loop commences, we have 'up-to' 20 threads executing against 1000 items in the iListOfItems collection. Each iteration executes on its own thread. Each thread will utilise a foreground thread when created by Parallel.ForEach. This means regardless of the main application shutdown, the app domain will be kept alive until all threads have finished.
However the user needs to close the application for some reason, say they close the form.
These 20 threads will continue to execute until all 1000 items are processed. This is not ideal in this scenario, as the application will not exit as the user expects and will continue to run behind the scenes, as can be seen by taking a look in task manger.
Say the user tries to rebuild the app again (VS 2010), it reports the exe is locked, then they would have to go into task manager to kill it or just wait until all 1000 items are processed.
I would not blame you for saying, but of course! I should be cancelling these threads using the CancellationTokenSource object and calling Cancel ... but there are some problems with this as of .net 4.0. Firstly this is still never going to result in a thread abort which would offer up an abort exception followed by thread termination, so the app domain will instead need to wait for the threads to finish normally, and this means waiting for the last blocking call, which would be the very last running iteration (thread) that ultimately gets to call po.CancellationToken.ThrowIfCancellationRequested.
In the example this would mean the app domain could still stay alive for up to 2 mins, even though the form has been closed and cancel called.
Note that Calling Cancel on CancellationTokenSource does not throw an exception on the processing thread(s), which would indeed act to interrupt the blocking call similar to a thread abort and stop the execution. An exception is cached ready for when all the other threads (concurrent iterations) eventually finish and return, the exception is thrown in the initiating thread (where the loop is declared).
I chose not to use the Cancel option on a CancellationTokenSource object. This is wasteful and arguably violates the well known anti-patten of controlling the flow of the code by Exceptions.
Instead, it is arguably 'better' to implement a simple thread safe property i.e. Bool stopExecuting. Then within the loop, check the value of stopExecuting and if the value is set to true by the external influence, we can take an alternate path to close down gracefully. Since we should not call cancel, this precludes checking CancellationTokenSource.IsCancellationRequested which would otherwise be another option.
Something like the following if condition would be appropriate within the loop;
if (loopState.ShouldExitCurrentIteration || loopState.IsExceptional || stopExecuting) {loopState.Stop(); return;}
The iteration will now exit in a 'controlled' manner as well as terminating further iterations, but as I said, this does little for our issue of having to wait on the long running and blocking call(s) that are made within each iteration (parallel loop thread), since these have to complete before each thread can get to the option of checking if it should stop.
In summary, as the user closes the form, the 20 threads will be signaled to stop via stopExecuting, but they will only stop when they have finished executing their long running function call.
We can't do anything about the fact that the application domain will always stay alive and only be released when all foreground threads have completed. And this means there will be a delay associated with waiting for any blocking calls made within the loop to complete.
Only a true thread abort can interrupt the blocking call, and you must mitigate leaving the system in a unstable/undefined state the best you can in the aborted thread's exception handler which goes without question. Whether that's appropriate is a matter for the programmer to decide, based on what resource handles they chose to maintain and how easy it is to close them in a thread's finally block. You could register with a token to terminate on cancel as a semi workaround i.e.
CancellationTokenSource cts = new CancellationTokenSource();
ParallelOptions po = new ParallelOptions();
po.CancellationToken = cts.Token;
po.MaxDegreeOfParallelism = System.Environment.ProcessorCount;
Parallel.ForEach(iListOfItems, po, (item, loopState) =>
{
using (cts.Token.Register(Thread.CurrentThread.Abort))
{
Try
{
Thread.Sleep(120000); // pretend web service call
}
Catch(ThreadAbortException ex)
{
// log etc.
}
Finally
{
// clean up here
}
}
});
but this will still result in an exception in the declaring thread.
All things considered, interrupt blocking calls using the parallel.loop constructs could have been a method on the options, avoiding the use of more obscure parts of the library. But why there is no option to cancel and avoid throwing an exception in the declaring method strikes me as a possible oversight.
But can I abort a Task (in .Net 4.0) in the same way not by
cancellation mechanism. I want to kill the Task immediately.
Other answerers have told you not to do it. But yes, you can do it. You can supply Thread.Abort() as the delegate to be called by the Task's cancellation mechanism. Here is how you could configure this:
class HardAborter
{
public bool WasAborted { get; private set; }
private CancellationTokenSource Canceller { get; set; }
private Task<object> Worker { get; set; }
public void Start(Func<object> DoFunc)
{
WasAborted = false;
// start a task with a means to do a hard abort (unsafe!)
Canceller = new CancellationTokenSource();
Worker = Task.Factory.StartNew(() =>
{
try
{
// specify this thread's Abort() as the cancel delegate
using (Canceller.Token.Register(Thread.CurrentThread.Abort))
{
return DoFunc();
}
}
catch (ThreadAbortException)
{
WasAborted = true;
return false;
}
}, Canceller.Token);
}
public void Abort()
{
Canceller.Cancel();
}
}
disclaimer: don't do this.
Here is an example of what not to do:
var doNotDoThis = new HardAborter();
// start a thread writing to the console
doNotDoThis.Start(() =>
{
while (true)
{
Thread.Sleep(100);
Console.Write(".");
}
return null;
});
// wait a second to see some output and show the WasAborted value as false
Thread.Sleep(1000);
Console.WriteLine("WasAborted: " + doNotDoThis.WasAborted);
// wait another second, abort, and print the time
Thread.Sleep(1000);
doNotDoThis.Abort();
Console.WriteLine("Abort triggered at " + DateTime.Now);
// wait until the abort finishes and print the time
while (!doNotDoThis.WasAborted) { Thread.CurrentThread.Join(0); }
Console.WriteLine("WasAborted: " + doNotDoThis.WasAborted + " at " + DateTime.Now);
Console.ReadKey();
You shouldn't use Thread.Abort()
Tasks can be Cancelled but not aborted.
The Thread.Abort() method is (severely) deprecated.
Both Threads and Tasks should cooperate when being stopped, otherwise you run the risk of leaving the system in a unstable/undefined state.
If you do need to run a Process and kill it from the outside, the only safe option is to run it in a separate AppDomain.
This answer is about .net 3.5 and earlier.
Thread-abort handling has been improved since then, a.o. by changing the way finally blocks work.
But Thread.Abort is still a suspect solution that you should always try to avoid.
And in .net Core (.net 5+) Thread.Abort() will now throw a PlatformNotSupportedException .
Kind of underscoring the 'deprecated' point.
Everyone knows (hopefully) its bad to terminate thread. The problem is when you don't own a piece of code you're calling. If this code is running in some do/while infinite loop , itself calling some native functions, etc. you're basically stuck. When this happens in your own code termination, stop or Dispose call, it's kinda ok to start shooting the bad guys (so you don't become a bad guy yourself).
So, for what it's worth, I've written those two blocking functions that use their own native thread, not a thread from the pool or some thread created by the CLR. They will stop the thread if a timeout occurs:
// returns true if the call went to completion successfully, false otherwise
public static bool RunWithAbort(this Action action, int milliseconds) => RunWithAbort(action, new TimeSpan(0, 0, 0, 0, milliseconds));
public static bool RunWithAbort(this Action action, TimeSpan delay)
{
if (action == null)
throw new ArgumentNullException(nameof(action));
var source = new CancellationTokenSource(delay);
var success = false;
var handle = IntPtr.Zero;
var fn = new Action(() =>
{
using (source.Token.Register(() => TerminateThread(handle, 0)))
{
action();
success = true;
}
});
handle = CreateThread(IntPtr.Zero, IntPtr.Zero, fn, IntPtr.Zero, 0, out var id);
WaitForSingleObject(handle, 100 + (int)delay.TotalMilliseconds);
CloseHandle(handle);
return success;
}
// returns what's the function should return if the call went to completion successfully, default(T) otherwise
public static T RunWithAbort<T>(this Func<T> func, int milliseconds) => RunWithAbort(func, new TimeSpan(0, 0, 0, 0, milliseconds));
public static T RunWithAbort<T>(this Func<T> func, TimeSpan delay)
{
if (func == null)
throw new ArgumentNullException(nameof(func));
var source = new CancellationTokenSource(delay);
var item = default(T);
var handle = IntPtr.Zero;
var fn = new Action(() =>
{
using (source.Token.Register(() => TerminateThread(handle, 0)))
{
item = func();
}
});
handle = CreateThread(IntPtr.Zero, IntPtr.Zero, fn, IntPtr.Zero, 0, out var id);
WaitForSingleObject(handle, 100 + (int)delay.TotalMilliseconds);
CloseHandle(handle);
return item;
}
[DllImport("kernel32")]
private static extern bool TerminateThread(IntPtr hThread, int dwExitCode);
[DllImport("kernel32")]
private static extern IntPtr CreateThread(IntPtr lpThreadAttributes, IntPtr dwStackSize, Delegate lpStartAddress, IntPtr lpParameter, int dwCreationFlags, out int lpThreadId);
[DllImport("kernel32")]
private static extern bool CloseHandle(IntPtr hObject);
[DllImport("kernel32")]
private static extern int WaitForSingleObject(IntPtr hHandle, int dwMilliseconds);
While it's possible to abort a thread, in practice it's almost always a very bad idea to do so. Aborthing a thread means the thread is not given a chance to clean up after itself, leaving resources undeleted, and things in unknown states.
In practice, if you abort a thread, you should only do so in conjunction with killing the process. Sadly, all too many people think ThreadAbort is a viable way of stopping something and continuing on, it's not.
Since Tasks run as threads, you can call ThreadAbort on them, but as with generic threads you almost never want to do this, except as a last resort.
I faced a similar problem with Excel's Application.Workbooks.
If the application is busy, the method hangs eternally. My approach was simply to try to get it in a task and wait, if it takes too long, I just leave the task be and go away (there is no harm "in this case", Excel will unfreeze the moment the user finishes whatever is busy).
In this case, it's impossible to use a cancellation token. The advantage is that I don't need excessive code, aborting threads, etc.
public static List<Workbook> GetAllOpenWorkbooks()
{
//gets all open Excel applications
List<Application> applications = GetAllOpenApplications();
//this is what we want to get from the third party library that may freeze
List<Workbook> books = null;
//as Excel may freeze here due to being busy, we try to get the workbooks asynchronously
Task task = Task.Run(() =>
{
try
{
books = applications
.SelectMany(app => app.Workbooks.OfType<Workbook>()).ToList();
}
catch { }
});
//wait for task completion
task.Wait(5000);
return books; //handle outside if books is null
}
This is my implementation of an idea presented by #Simon-Mourier, using the dotnet thread, short and simple code:
public static bool RunWithAbort(this Action action, int milliseconds)
{
if (action == null) throw new ArgumentNullException(nameof(action));
var success = false;
var thread = new Thread(() =>
{
action();
success = true;
});
thread.IsBackground = true;
thread.Start();
thread.Join(milliseconds);
thread.Abort();
return success;
}
You can "abort" a task by running it on a thread you control and aborting that thread. This causes the task to complete in a faulted state with a ThreadAbortException. You can control thread creation with a custom task scheduler, as described in this answer. Note that the caveat about aborting a thread applies.
(If you don't ensure the task is created on its own thread, aborting it would abort either a thread-pool thread or the thread initiating the task, neither of which you typically want to do.)
using System;
using System.Threading;
using System.Threading.Tasks;
...
var cts = new CancellationTokenSource();
var task = Task.Run(() => { while (true) { } });
Parallel.Invoke(() =>
{
task.Wait(cts.Token);
}, () =>
{
Thread.Sleep(1000);
cts.Cancel();
});
This is a simple snippet to abort a never-ending task with CancellationTokenSource.
I'm writing a Windows Service that will kick off multiple worker threads that will listen to Amazon SQS queues and process messages. There will be about 20 threads listening to 10 queues.
The threads will have to be always running and that's why I'm leaning towards to actually using actual threads for the worker loops rather than threadpool threads.
Here is a top level implementation. Windows service will kick off multiple worker threads and each will listen to it's queue and process messages.
protected override void OnStart(string[] args)
{
for (int i = 0; i < _workers; i++)
{
new Thread(RunWorker).Start();
}
}
Here is the implementation of the work
public async void RunWorker()
{
while(true)
{
// .. get message from amazon sqs sync.. about 20ms
var message = sqsClient.ReceiveMessage();
try
{
await PerformWebRequestAsync(message);
await InsertIntoDbAsync(message);
}
catch(SomeExeception)
{
// ... log
//continue to retry
continue;
}
sqsClient.DeleteMessage();
}
}
I know I can perform the same operation with Task.Run and execute it on the threadpool thread rather than starting individual thread, but I don't see a reason for that since each thread will always be running.
Do you see any problems with this implementation? How reliable would it be to leave threads always running in this fashion and what can I do to make sure that each thread is always running?
One problem with your existing solution is that you call your RunWorker in a fire-and-forget manner, albeit on a new thread (i.e., new Thread(RunWorker).Start()).
RunWorker is an async method, it will return to the caller when the execution point hits the first await (i.e. await PerformWebRequestAsync(message)). If PerformWebRequestAsync returns a pending task, RunWorker returns and the new thread you just started terminates.
I don't think you need a new thread here at all, just use AmazonSQSClient.ReceiveMessageAsync and await its result. Another thing is that you shouldn't be using async void methods unless you really don't care about tracking the state of the asynchronous task. Use async Task instead.
Your code might look like this:
List<Task> _workers = new List<Task>();
CancellationTokenSource _cts = new CancellationTokenSource();
protected override void OnStart(string[] args)
{
for (int i = 0; i < _MAX_WORKERS; i++)
{
_workers.Add(RunWorkerAsync(_cts.Token));
}
}
public async Task RunWorkerAsync(CancellationToken token)
{
while(true)
{
token.ThrowIfCancellationRequested();
// .. get message from amazon sqs sync.. about 20ms
var message = await sqsClient.ReceiveMessageAsync().ConfigureAwait(false);
try
{
await PerformWebRequestAsync(message);
await InsertIntoDbAsync(message);
}
catch(SomeExeception)
{
// ... log
//continue to retry
continue;
}
sqsClient.DeleteMessage();
}
}
Now, to stop all pending workers, you could simple do this (from the main "request dispatcher" thread):
_cts.Cancel();
try
{
Task.WaitAll(_workers.ToArray());
}
catch (AggregateException ex)
{
ex.Handle(inner => inner is OperationCanceledException);
}
Note, ConfigureAwait(false) is optional for Windows Service, because there's no synchronization context on the initial thread, by default. However, I'd keep it that way to make the code independent of the execution environment (for cases where there is synchronization context).
Finally, if for some reason you cannot use ReceiveMessageAsync, or you need to call another blocking API, or simply do a piece of CPU intensive work at the beginning of RunWorkerAsync, just wrap it with Task.Run (as opposed to wrapping the whole RunWorkerAsync):
var message = await Task.Run(
() => sqsClient.ReceiveMessage()).ConfigureAwait(false);
Well, for one I'd use a CancellationTokenSource instantiated in the service and passed down to the workers. Your while statement would become:
while(!cancellationTokenSource.IsCancellationRequested)
{
//rest of the code
}
This way you can cancel all your workers from the OnStop service method.
Additionally, you should watch for:
If you're playing with thread states from outside of the thread, then a ThreadStateException, or ThreadInterruptedException or one of the others might be thrown. So, you want to handle a proper thread restart.
Do the workers need to run without pause in-between iterations? I would throw in a sleep in there (even a few ms's) just so they don't keep the CPU up for nothing.
You need to handle ThreadStartException and restart the worker, if it occurs.
Other than that there's no reason why those 10 treads can't run for as long as the service runs (days, weeks, months at a time).
i have an application who take all the added files from my Listbox and play this files:
IEnumerable<string> source
public void play()
{
Task.Factory.StartNew(() =>
{
Parallel.ForEach(source,
new ParallelOptions
{
MaxDegreeOfParallelism = 1 //limit number of parallel threads
},
file =>
{
//each file process via another class
});
}).ContinueWith(
t =>
{
OnFinishPlayEvent();
}
, TaskScheduler.FromCurrentSynchronizationContext() //to ContinueWith (update UI) from UI thread
);
}
my processing file can be stop via my class property but if i want to stop all the files
that waiting how can i do it ?
You need to design your routines to accept a CancellationToken, and then trigger a CancellationTokenSource.Cancel().
This will allow you to provide a mechanism to cooperatively cancel your work.
For details, see Cancellation in Managed Threads and Task Cancellation on MSDN.
If you want to stop a parallel loop, use an instance of the ParallelLoopState class. To cancel a task, you want to use a CancellationToken. Since you are embedding your parallel loop inside a task, you can simply pass a cancellation token into the task. Bear in mind, this will throw an OperationCanceledException you will have to catch, if you choose to wait on your task(s).
For example, and for the sake of argument, we'll assume that something else will call a delegate inside your class that will set the cancellation token.
CancellationTokenSource _tokenSource = new CancellationTokenSource();
//Let's assume this is set as the delegate to some other event
//that requests cancellation of your task
void Cancel(object sender, EventArgs e)
{
_tokenSource.Cancel();
}
void DoSomething()
{
var task = Task.Factory.StartNew(() => {
// Your code here...
}, _tokenSource.Token);
try {
task.Wait();
}
catch (OperationCanceledException) {
//Carry on, logging that the task was canceled, if you like
}
catch (AggregateException ax) {
//Your task will throw an AggregateException if an unhandled exception is thrown
//from the worker. You will want to use this block to do whatever exception handling
//you do.
}
}
Bear in mind, there are better ways to do this (and I'm typing from memory here, so there could be some syntax errors and the like), but this should get you started.