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TaskObservableExtensions.cs
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TaskObservableExtensions.cs
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// this code is borrowed from RxOfficial(rx.codeplex.com) and modified
#if (NET_4_6 || NET_STANDARD_2_0)
using System;
using System.Threading.Tasks;
using System.Threading;
namespace UniRx
{
/// <summary>
/// Provides a set of static methods for converting tasks to observable sequences.
/// </summary>
public static class TaskObservableExtensions
{
/// <summary>
/// Returns an observable sequence that signals when the task completes.
/// </summary>
/// <param name="task">Task to convert to an observable sequence.</param>
/// <returns>An observable sequence that produces a unit value when the task completes, or propagates the exception produced by the task.</returns>
/// <exception cref="ArgumentNullException"><paramref name="task"/> is null.</exception>
/// <remarks>If the specified task object supports cancellation, consider using <see cref="Observable.FromAsync(Func{CancellationToken, Task})"/> instead.</remarks>
public static IObservable<Unit> ToObservable(this Task task)
{
if (task == null)
throw new ArgumentNullException("task");
return ToObservableImpl(task, null);
}
/// <summary>
/// Returns an observable sequence that signals when the task completes.
/// </summary>
/// <param name="task">Task to convert to an observable sequence.</param>
/// <param name="scheduler">Scheduler on which to notify observers about completion, cancellation or failure.</param>
/// <returns>An observable sequence that produces a unit value when the task completes, or propagates the exception produced by the task.</returns>
/// <exception cref="ArgumentNullException"><paramref name="task"/> is null or <paramref name="scheduler"/> is null.</exception>
/// <remarks>If the specified task object supports cancellation, consider using <see cref="Observable.FromAsync(Func{CancellationToken, Task})"/> instead.</remarks>
public static IObservable<Unit> ToObservable(this Task task, IScheduler scheduler)
{
if (task == null)
throw new ArgumentNullException("task");
if (scheduler == null)
throw new ArgumentNullException("scheduler");
return ToObservableImpl(task, scheduler);
}
private static IObservable<Unit> ToObservableImpl(Task task, IScheduler scheduler)
{
var res = default(IObservable<Unit>);
if (task.IsCompleted)
{
scheduler = scheduler ?? Scheduler.Immediate;
switch (task.Status)
{
case TaskStatus.RanToCompletion:
res = Observable.Return<Unit>(Unit.Default, scheduler);
break;
case TaskStatus.Faulted:
res = Observable.Throw<Unit>(task.Exception.InnerException, scheduler);
break;
case TaskStatus.Canceled:
res = Observable.Throw<Unit>(new TaskCanceledException(task), scheduler);
break;
}
}
else
{
//
// Separate method to avoid closure in synchronous completion case.
//
res = ToObservableSlow(task, scheduler);
}
return res;
}
private static IObservable<Unit> ToObservableSlow(Task task, IScheduler scheduler)
{
var subject = new AsyncSubject<Unit>();
var options = GetTaskContinuationOptions(scheduler);
task.ContinueWith(t => ToObservableDone(task, subject), options);
return ToObservableResult(subject, scheduler);
}
private static void ToObservableDone(Task task, IObserver<Unit> subject)
{
switch (task.Status)
{
case TaskStatus.RanToCompletion:
subject.OnNext(Unit.Default);
subject.OnCompleted();
break;
case TaskStatus.Faulted:
subject.OnError(task.Exception.InnerException);
break;
case TaskStatus.Canceled:
subject.OnError(new TaskCanceledException(task));
break;
}
}
/// <summary>
/// Returns an observable sequence that propagates the result of the task.
/// </summary>
/// <typeparam name="TResult">The type of the result produced by the task.</typeparam>
/// <param name="task">Task to convert to an observable sequence.</param>
/// <returns>An observable sequence that produces the task's result, or propagates the exception produced by the task.</returns>
/// <exception cref="ArgumentNullException"><paramref name="task"/> is null.</exception>
/// <remarks>If the specified task object supports cancellation, consider using <see cref="Observable.FromAsync{TResult}(Func{CancellationToken, Task{TResult}})"/> instead.</remarks>
public static IObservable<TResult> ToObservable<TResult>(this Task<TResult> task)
{
if (task == null)
throw new ArgumentNullException("task");
return ToObservableImpl(task, null);
}
/// <summary>
/// Returns an observable sequence that propagates the result of the task.
/// </summary>
/// <typeparam name="TResult">The type of the result produced by the task.</typeparam>
/// <param name="task">Task to convert to an observable sequence.</param>
/// <param name="scheduler">Scheduler on which to notify observers about completion, cancellation or failure.</param>
/// <returns>An observable sequence that produces the task's result, or propagates the exception produced by the task.</returns>
/// <exception cref="ArgumentNullException"><paramref name="task"/> is null or <paramref name="scheduler"/> is null.</exception>
/// <remarks>If the specified task object supports cancellation, consider using <see cref="Observable.FromAsync{TResult}(Func{CancellationToken, Task{TResult}})"/> instead.</remarks>
public static IObservable<TResult> ToObservable<TResult>(this Task<TResult> task, IScheduler scheduler)
{
if (task == null)
throw new ArgumentNullException("task");
if (scheduler == null)
throw new ArgumentNullException("scheduler");
return ToObservableImpl(task, scheduler);
}
private static IObservable<TResult> ToObservableImpl<TResult>(Task<TResult> task, IScheduler scheduler)
{
var res = default(IObservable<TResult>);
if (task.IsCompleted)
{
scheduler = scheduler ?? Scheduler.Immediate;
switch (task.Status)
{
case TaskStatus.RanToCompletion:
res = Observable.Return<TResult>(task.Result, scheduler);
break;
case TaskStatus.Faulted:
res = Observable.Throw<TResult>(task.Exception.InnerException, scheduler);
break;
case TaskStatus.Canceled:
res = Observable.Throw<TResult>(new TaskCanceledException(task), scheduler);
break;
}
}
else
{
//
// Separate method to avoid closure in synchronous completion case.
//
res = ToObservableSlow(task, scheduler);
}
return res;
}
private static IObservable<TResult> ToObservableSlow<TResult>(Task<TResult> task, IScheduler scheduler)
{
var subject = new AsyncSubject<TResult>();
var options = GetTaskContinuationOptions(scheduler);
task.ContinueWith(t => ToObservableDone(task, subject), options);
return ToObservableResult(subject, scheduler);
}
private static void ToObservableDone<TResult>(Task<TResult> task, IObserver<TResult> subject)
{
switch (task.Status)
{
case TaskStatus.RanToCompletion:
subject.OnNext(task.Result);
subject.OnCompleted();
break;
case TaskStatus.Faulted:
subject.OnError(task.Exception.InnerException);
break;
case TaskStatus.Canceled:
subject.OnError(new TaskCanceledException(task));
break;
}
}
private static TaskContinuationOptions GetTaskContinuationOptions(IScheduler scheduler)
{
var options = TaskContinuationOptions.None;
if (scheduler != null)
{
//
// We explicitly don't special-case the immediate scheduler here. If the user asks for a
// synchronous completion, we'll try our best. However, there's no guarantee due to the
// internal stack probing in the TPL, which may cause asynchronous completion on a thread
// pool thread in order to avoid stack overflows. Therefore we can only attempt to be more
// efficient in the case where the user specified a scheduler, hence we know that the
// continuation will trigger a scheduling operation. In case of the immediate scheduler,
// it really becomes "immediate scheduling" wherever the TPL decided to run the continuation,
// i.e. not necessarily where the task was completed from.
//
options |= TaskContinuationOptions.ExecuteSynchronously;
}
return options;
}
private static IObservable<TResult> ToObservableResult<TResult>(AsyncSubject<TResult> subject, IScheduler scheduler)
{
if (scheduler != null)
{
return subject.ObserveOn(scheduler);
}
else
{
return subject.AsObservable();
}
}
/// <summary>
/// Returns a task that will receive the last value or the exception produced by the observable sequence.
/// </summary>
/// <typeparam name="TResult">The type of the elements in the source sequence.</typeparam>
/// <param name="observable">Observable sequence to convert to a task.</param>
/// <returns>A task that will receive the last element or the exception produced by the observable sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="observable"/> is null.</exception>
public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable)
{
if (observable == null)
throw new ArgumentNullException("observable");
return observable.ToTask(new CancellationToken(), null);
}
/// <summary>
/// Returns a task that will receive the last value or the exception produced by the observable sequence.
/// </summary>
/// <typeparam name="TResult">The type of the elements in the source sequence.</typeparam>
/// <param name="observable">Observable sequence to convert to a task.</param>
/// <param name="state">The state to use as the underlying task's AsyncState.</param>
/// <returns>A task that will receive the last element or the exception produced by the observable sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="observable"/> is null.</exception>
public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable, object state)
{
if (observable == null)
throw new ArgumentNullException("observable");
return observable.ToTask(new CancellationToken(), state);
}
/// <summary>
/// Returns a task that will receive the last value or the exception produced by the observable sequence.
/// </summary>
/// <typeparam name="TResult">The type of the elements in the source sequence.</typeparam>
/// <param name="observable">Observable sequence to convert to a task.</param>
/// <param name="cancellationToken">Cancellation token that can be used to cancel the task, causing unsubscription from the observable sequence.</param>
/// <returns>A task that will receive the last element or the exception produced by the observable sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="observable"/> is null.</exception>
public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable, CancellationToken cancellationToken)
{
if (observable == null)
throw new ArgumentNullException("observable");
return observable.ToTask(cancellationToken, null);
}
/// <summary>
/// Returns a task that will receive the last value or the exception produced by the observable sequence.
/// </summary>
/// <typeparam name="TResult">The type of the elements in the source sequence.</typeparam>
/// <param name="observable">Observable sequence to convert to a task.</param>
/// <param name="cancellationToken">Cancellation token that can be used to cancel the task, causing unsubscription from the observable sequence.</param>
/// <param name="state">The state to use as the underlying task's AsyncState.</param>
/// <returns>A task that will receive the last element or the exception produced by the observable sequence.</returns>
/// <exception cref="ArgumentNullException"><paramref name="observable"/> is null.</exception>
public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable, CancellationToken cancellationToken, object state)
{
if (observable == null)
throw new ArgumentNullException("observable");
var hasValue = false;
var lastValue = default(TResult);
var tcs = new TaskCompletionSource<TResult>(state);
var disposable = new SingleAssignmentDisposable();
var ctr = default(CancellationTokenRegistration);
if (cancellationToken.CanBeCanceled)
{
ctr = cancellationToken.Register(() =>
{
disposable.Dispose();
tcs.TrySetCanceled(cancellationToken);
});
}
var taskCompletionObserver = Observer.Create<TResult>(
value =>
{
hasValue = true;
lastValue = value;
},
ex =>
{
tcs.TrySetException(ex);
ctr.Dispose(); // no null-check needed (struct)
disposable.Dispose();
},
() =>
{
if (hasValue)
tcs.TrySetResult(lastValue);
else
tcs.TrySetException(new InvalidOperationException("Strings_Linq.NO_ELEMENTS"));
ctr.Dispose(); // no null-check needed (struct)
disposable.Dispose();
}
);
//
// Subtle race condition: if the source completes before we reach the line below, the SingleAssigmentDisposable
// will already have been disposed. Upon assignment, the disposable resource being set will be disposed on the
// spot, which may throw an exception. (Similar to TFS 487142)
//
try
{
//
// [OK] Use of unsafe Subscribe: we're catching the exception here to set the TaskCompletionSource.
//
// Notice we could use a safe subscription to route errors through OnError, but we still need the
// exception handling logic here for the reason explained above. We cannot afford to throw here
// and as a result never set the TaskCompletionSource, so we tunnel everything through here.
//
disposable.Disposable = observable.Subscribe/*Unsafe*/(taskCompletionObserver);
}
catch (Exception ex)
{
tcs.TrySetException(ex);
}
return tcs.Task;
}
}
}
#endif