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osu-lazer/osu.Game/Extensions/TaskExtensions.cs

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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
#nullable enable
using System;
using System.Threading;
using System.Threading.Tasks;
using osu.Framework.Extensions.ObjectExtensions;
namespace osu.Game.Extensions
{
public static class TaskExtensions
{
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/// <summary>
/// Add a continuation to be performed only after the attached task has completed.
/// </summary>
/// <param name="task">The previous task to be awaited on.</param>
/// <param name="action">The action to run.</param>
/// <param name="cancellationToken">An optional cancellation token. Will only cancel the provided action, not the sequence.</param>
/// <returns>A task representing the provided action.</returns>
public static Task ContinueWithSequential(this Task task, Action action, CancellationToken cancellationToken = default) =>
task.ContinueWithSequential(() => Task.Run(action, cancellationToken), cancellationToken);
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/// <summary>
/// Add a continuation to be performed only after the attached task has completed.
/// </summary>
/// <param name="task">The previous task to be awaited on.</param>
/// <param name="continuationFunction">The continuation to run. Generally should be an async function.</param>
/// <param name="cancellationToken">An optional cancellation token. Will only cancel the provided action, not the sequence.</param>
/// <returns>A task representing the provided action.</returns>
public static Task ContinueWithSequential(this Task task, Func<Task> continuationFunction, CancellationToken cancellationToken = default)
{
var tcs = new TaskCompletionSource<bool>();
task.ContinueWith(t =>
{
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// the previous task has finished execution or been cancelled, so we can run the provided continuation.
if (cancellationToken.IsCancellationRequested)
{
tcs.SetCanceled();
}
else
{
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continuationFunction().ContinueWith(continuationTask =>
{
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if (cancellationToken.IsCancellationRequested || continuationTask.IsCanceled)
{
tcs.TrySetCanceled();
}
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else if (continuationTask.IsFaulted)
{
tcs.TrySetException(continuationTask.Exception.AsNonNull());
}
else
{
tcs.TrySetResult(true);
}
}, cancellationToken: default);
}
}, cancellationToken: default);
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// importantly, we are not returning the continuation itself but rather a task which represents its status in sequential execution order.
// this will not be cancelled or completed until the previous task has also.
return tcs.Task;
}
}
}