実際、これは TPL に関する問題というよりも、ラムダの重いコードのテスト可能性に関する問題です。Hightechrider の提案は良いものですが、基本的に、テストはコードと同じくらい TPL をテストしています。最初のタスクが終了し、ContinueWith が次のタスクを開始するときにそれをテストする必要はありません。
ラムダ内のコードが非常に大きい場合、明確に定義されたパラメーターを使用して、よりテストしやすいメソッドにコードを引き出すと、読みやすく、よりテストしやすいコードになる可能性があります。その周りに単体テストを書くことができます。可能であれば、単体テストから並列処理を制限または削除しようとします。
スケジューラのアプローチが機能するかどうかを確認したかったと言いました。http://code.msdn.microsoft.com/ParExtSamplesから変更された StaTaskScheduler を使用した実装を次に示します。
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Xunit;
namespace Example
{
public class Foo
{
private TaskScheduler _scheduler;
public int Bar { get; set; }
private void SomethingLong()
{
Thread.SpinWait(10000);
}
public Foo()
: this(TaskScheduler.Default)
{
}
public Foo(TaskScheduler scheduler)
{
_scheduler = scheduler;
}
public void DoWork()
{
var factory = new TaskFactory(_scheduler);
factory.StartNew(() => SomethingLong())
.ContinueWith(a => Bar = 1, _scheduler);
}
}
public class FooTests
{
[Fact]
public void Foo_should_set_Bar_to_1()
{
var sch = new StaTaskScheduler(3);
var target = new Foo(sch);
target.DoWork();
sch.Dispose();
Assert.Equal(1, target.Bar);
}
}
public sealed class StaTaskScheduler : TaskScheduler, IDisposable
{
/// <summary>Stores the queued tasks to be executed by our pool of STA threads.</summary>
private BlockingCollection<Task> _tasks;
/// <summary>The STA threads used by the scheduler.</summary>
private readonly List<Thread> _threads;
/// <summary>Initializes a new instance of the StaTaskScheduler class with the specified concurrency level.</summary>
/// <param name="numberOfThreads">The number of threads that should be created and used by this scheduler.</param>
public StaTaskScheduler(int numberOfThreads)
{
// Validate arguments
if (numberOfThreads < 1) throw new ArgumentOutOfRangeException("concurrencyLevel");
// Initialize the tasks collection
_tasks = new BlockingCollection<Task>();
// Create the threads to be used by this scheduler
_threads = Enumerable.Range(0, numberOfThreads).Select(i =>
{
var thread = new Thread(() =>
{
// Continually get the next task and try to execute it.
// This will continue until the scheduler is disposed and no more tasks remain.
foreach (var t in _tasks.GetConsumingEnumerable())
{
TryExecuteTask(t);
}
});
thread.IsBackground = true;
// NO STA REQUIREMENT!
// thread.SetApartmentState(ApartmentState.STA);
return thread;
}).ToList();
// Start all of the threads
_threads.ForEach(t => t.Start());
}
/// <summary>Queues a Task to be executed by this scheduler.</summary>
/// <param name="task">The task to be executed.</param>
protected override void QueueTask(Task task)
{
// Push it into the blocking collection of tasks
_tasks.Add(task);
}
/// <summary>Provides a list of the scheduled tasks for the debugger to consume.</summary>
/// <returns>An enumerable of all tasks currently scheduled.</returns>
protected override IEnumerable<Task> GetScheduledTasks()
{
// Serialize the contents of the blocking collection of tasks for the debugger
return _tasks.ToArray();
}
/// <summary>Determines whether a Task may be inlined.</summary>
/// <param name="task">The task to be executed.</param>
/// <param name="taskWasPreviouslyQueued">Whether the task was previously queued.</param>
/// <returns>true if the task was successfully inlined; otherwise, false.</returns>
protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
{
// Try to inline if the current thread is STA
return
Thread.CurrentThread.GetApartmentState() == ApartmentState.STA &&
TryExecuteTask(task);
}
/// <summary>Gets the maximum concurrency level supported by this scheduler.</summary>
public override int MaximumConcurrencyLevel
{
get { return _threads.Count; }
}
/// <summary>
/// Cleans up the scheduler by indicating that no more tasks will be queued.
/// This method blocks until all threads successfully shutdown.
/// </summary>
public void Dispose()
{
if (_tasks != null)
{
// Indicate that no new tasks will be coming in
_tasks.CompleteAdding();
// Wait for all threads to finish processing tasks
foreach (var thread in _threads) thread.Join();
// Cleanup
_tasks.Dispose();
_tasks = null;
}
}
}
}