modules/platforms/dotnet/Apache.Ignite.Core/Impl/Common/TaskRunner.cs

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace Apache.Ignite.Core.Impl.Common
{
    using System;
    using System.Collections.Generic;
    using System.Threading;
    using System.Threading.Tasks;

    /// <summary>
    /// Extensions for <see cref="Task"/> classes.
    /// Fixes the issue with <see cref="TaskScheduler.Current"/> being used by default by system APIs.
    /// Current scheduler can be anything, but in most cases we just want thread pool when starting a task.
    /// <see cref="TaskScheduler.Default"/> is normally ThreadPoolTaskScheduler.
    /// </summary>
    internal static class TaskRunner
    {
        /// <summary>
        /// Gets the completed task.
        /// <para />
        /// Task.CompletedTask is not available on .NET 4.
        /// </summary>
        public static readonly Task CompletedTask = FromResult<object>(null);

        /// <summary>
        /// ContinueWith using default scheduler.
        /// </summary>
        public static Task<TNewResult> ContWith<TResult, TNewResult>(this Task<TResult> task,
            Func<Task<TResult>, TNewResult> continuationFunction,
            TaskContinuationOptions continuationOptions = TaskContinuationOptions.None)
        {
            IgniteArgumentCheck.NotNull(task, "task");

            return task.ContinueWith(continuationFunction, CancellationToken.None, continuationOptions,
                TaskScheduler.Default);
        }

        /// <summary>
        /// ContinueWith using default scheduler.
        /// </summary>
        public static Task ContWith(this Task task,
            Action<Task> continuationFunction,
            TaskContinuationOptions continuationOptions = TaskContinuationOptions.None)
        {
            IgniteArgumentCheck.NotNull(task, "task");

            return task.ContinueWith(continuationFunction, CancellationToken.None, continuationOptions,
                TaskScheduler.Default);
        }

        /// <summary>
        /// Run new task using default scheduler.
        /// </summary>
        public static Task Run(Action action,
            TaskCreationOptions options = TaskCreationOptions.None)
        {
            return Task.Factory.StartNew(action, CancellationToken.None, options,
                TaskScheduler.Default);
        }

        /// <summary>
        /// Run new task using default scheduler.
        /// </summary>
        public static Task<TResult> Run<TResult>(Func<TResult> func)
        {
            return Task.Factory.StartNew(func, CancellationToken.None, TaskCreationOptions.None,
                TaskScheduler.Default);
        }

        /// <summary>
        /// Gets a completed task from a given result.
        /// </summary>
        public static Task<TResult> FromResult<TResult>(TResult result)
        {
            var tcs = new TaskCompletionSource<TResult>();
            tcs.SetResult(result);
            return tcs.Task;
        }

        /// <summary>
        /// Creates a task that will complete when all of the supplied tasks have completed.
        /// <para />
        /// Task.WhenAll is not available on .NET 4.
        /// </summary>
        public static Task WhenAll(Task[] tasks)
        {
            if (tasks.Length == 0)
            {
                return CompletedTask;
            }

            if (tasks.Length == 1)
            {
                return tasks[0];
            }

            return Task.Factory.ContinueWhenAll(tasks, _ =>
            {
                var errs = new List<Exception>(tasks.Length);

                foreach (var task in tasks)
                {
                    if (task.Exception != null)
                    {
                        // ReSharper disable once PossibleNullReferenceException
                        errs.Add(task.Exception.GetBaseException());
                    }
                }

                if (errs.Count > 0)
                {
                    throw new AggregateException(errs);
                }
            });
        }

        /// <summary>
        /// Sets this task as result for a <see cref="TaskCompletionSource{TResult}"/>.
        /// </summary>
        public static void SetAsResult<T>(this Task task, TaskCompletionSource<T> tcs)
        {
            if (task.IsCanceled)
            {
                tcs.SetCanceled();
            }
            else if (task.Exception != null)
            {
                tcs.SetException(task.Exception);
            }
            else
            {
                tcs.SetResult(default(T));
            }
        }
    }
}