/// <summary>
/// Stops work gracefully. All backlog will be processed.
/// </summary>
public void Complete()
{
switch (State)
{
case States.Idle:
_completionSource.TrySetResult();
break;
case States.Processing:
State = States.FinalProcessing;
break;
case States.FinalProcessing:
case States.Aborted:
break;
default:
throw new ArgumentOutOfRangeException(nameof(State), "Unexpected state.");
}
}
/// <summary> /// Attempts to transition the underlying task into the <see cref="SystemTasks.TaskStatus.RanToCompletion"/> state. /// </summary> public static bool TrySetResult(SystemTaskCompletionSource tcs) => tcs.TrySetResult();
/// <summary></summary>
/// <typeparam name="TResult"></typeparam>
/// <param name="tasks"></param>
/// <returns></returns>
public static Task <Task <TResult> > WhenAny <TResult>(IEnumerable <Task <TResult> > tasks)
{
if (tasks == null)
{
throw new ArgumentNullException("tasks");
}
Contract.EndContractBlock();
var tcs = new TaskCompletionSource <Task <TResult> >();
Task.Factory.ContinueWhenAny((tasks as Task <TResult>[]) ?? tasks.ToArray(), (Task <TResult> completed) => tcs.TrySetResult(completed), CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
return(tcs.Task);
}
/// <summary>
/// Asynchronously iterates through an enumerable of tasks.
/// </summary>
/// <param name="factory">The target factory.</param>
/// <param name="source">The enumerable containing the tasks to be iterated through.</param>
/// <param name="state">The asynchronous state for the returned Task.</param>
/// <param name="cancellationToken">The cancellation token used to cancel the iteration.</param>
/// <param name="creationOptions">Options that control the task's behavior.</param>
/// <param name="scheduler">The scheduler to which tasks will be scheduled.</param>
/// <returns>A Task that represents the complete asynchronous operation.</returns>
public static Task Iterate(this TaskFactory factory, IEnumerable <object> source, object state, CancellationToken cancellationToken, TaskCreationOptions creationOptions, TaskScheduler scheduler)
{
// Validate/update parameters
Contract.Requires(factory != null);
Contract.Requires(source != null);
Contract.Requires(scheduler != null);
// Get an enumerator from the enumerable
var enumerator = source.GetEnumerator();
if (enumerator == null)
{
throw new InvalidOperationException("Invalid enumerable - GetEnumerator returned null");
}
// Create the task to be returned to the caller. And ensure
// that when everything is done, the enumerator is cleaned up.
var trs = new TaskCompletionSource <object>(state, creationOptions);
trs.Task.ContinueWith(_ => enumerator.Dispose(), CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
// This will be called every time more work can be done.
Action <Task> recursiveBody = null;
recursiveBody = antecedent =>
{
try
{
// If we should continue iterating and there's more to iterate
// over, create a continuation to continue processing. We only
// want to continue processing once the current Task (as yielded
// from the enumerator) is complete.
if (enumerator.MoveNext())
{
var nextItem = enumerator.Current;
// If we got a Task, continue from it to continue iterating
if (nextItem is Task)
{
var nextTask = (Task)nextItem;
nextTask.IgnoreExceptions(); // TODO: Is this a good idea?
nextTask.ContinueWith(recursiveBody).IgnoreExceptions();
}
//// If we got a scheduler, continue iterating under the new scheduler,
//// enabling hopping between contexts.
else if (nextItem is TaskScheduler)
{
Task.Factory.StartNew(() => recursiveBody(null), CancellationToken.None, TaskCreationOptions.None, (TaskScheduler)nextItem).IgnoreExceptions();
}
//// Anything else is invalid
else
{
trs.TrySetException(new InvalidOperationException("Task or TaskScheduler object expected in Iterate"));
}
}
//// Otherwise, we're done!
else
{
trs.TrySetResult(null);
}
}
//// If MoveNext throws an exception, propagate that to the user,
//// either as cancellation or as a fault
catch (Exception exc)
{
var oce = exc as OperationCanceledException;
if (oce != null && oce.CancellationToken == cancellationToken)
{
trs.TrySetCanceled();
}
else
{
trs.TrySetException(exc);
}
}
};
// Get things started by launching the first task
factory.StartNew(() => recursiveBody(null), CancellationToken.None, TaskCreationOptions.None, scheduler).IgnoreExceptions();
// Return the representative task to the user
return(trs.Task);
}
