TaskScheduler TaskScheduler TaskScheduler TaskScheduler Class

Definizione

Rappresenta un oggetto che gestisce le operazioni di basso livello relative all'accodamento delle attività nei thread.Represents an object that handles the low-level work of queuing tasks onto threads.

public ref class TaskScheduler abstract
public abstract class TaskScheduler
type TaskScheduler = class
Public MustInherit Class TaskScheduler
Ereditarietà
TaskSchedulerTaskSchedulerTaskSchedulerTaskScheduler

Esempi

L'esempio seguente è tratto dagli esempi per la programmazione parallela con il .NET Framework 4 sul sito Web MSDN Code Gallery.The following example is taken from the Samples for Parallel Programming with the .NET Framework 4 on the MSDN Code Gallery Web site. Viene creata un'utilità di pianificazione personalizzata che limita il numero di thread usati dall'app.It creates a custom task scheduler that limits the number of threads used by the app. Vengono quindi avviati due set di attività e vengono visualizzate le informazioni sull'attività e sul thread in cui è in esecuzione l'attività.It then launches two sets of tasks and displays information about the task and the thread on which the task is executing.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

class Example
{
   static void Main()
   {
       // Create a scheduler that uses two threads. 
       LimitedConcurrencyLevelTaskScheduler lcts = new LimitedConcurrencyLevelTaskScheduler(2);
       List<Task> tasks = new List<Task>();
       
       // Create a TaskFactory and pass it our custom scheduler. 
       TaskFactory factory = new TaskFactory(lcts);
       CancellationTokenSource cts = new CancellationTokenSource();
       
       // Use our factory to run a set of tasks. 
       Object lockObj = new Object();
       int outputItem = 0;
       
       for (int tCtr = 0; tCtr <= 4; tCtr++) {
          int iteration = tCtr;
          Task t = factory.StartNew(() => {
                                       for (int i = 0; i < 1000; i++) {
                                          lock (lockObj) {
                                             Console.Write("{0} in task t-{1} on thread {2}   ", 
                                                           i, iteration, Thread.CurrentThread.ManagedThreadId);
                                             outputItem++;
                                             if (outputItem % 3 == 0)
                                                Console.WriteLine();
                                          }
                                       }                   
                                    }, cts.Token);
          tasks.Add(t);                      
      }
      // Use it to run a second set of tasks.                       
      for (int tCtr = 0; tCtr <= 4; tCtr++) {
         int iteration = tCtr;
         Task t1 = factory.StartNew(() => {
                                       for (int outer = 0; outer <= 10; outer++) {
                                          for (int i = 0x21; i <= 0x7E; i++) {
                                             lock (lockObj) {
                                                Console.Write("'{0}' in task t1-{1} on thread {2}   ", 
                                                              Convert.ToChar(i), iteration, Thread.CurrentThread.ManagedThreadId);
                                                outputItem++;
                                                if (outputItem % 3 == 0)
                                                   Console.WriteLine();
                                             } 
                                          }
                                       }                                           
                                    }, cts.Token);           
         tasks.Add(t1);
      }
      
      // Wait for the tasks to complete before displaying a completion message.
      Task.WaitAll(tasks.ToArray());
      cts.Dispose();
      Console.WriteLine("\n\nSuccessful completion.");
   }
}

// Provides a task scheduler that ensures a maximum concurrency level while 
// running on top of the thread pool.
public class LimitedConcurrencyLevelTaskScheduler : TaskScheduler
{
   // Indicates whether the current thread is processing work items.
   [ThreadStatic]
   private static bool _currentThreadIsProcessingItems;

  // The list of tasks to be executed 
   private readonly LinkedList<Task> _tasks = new LinkedList<Task>(); // protected by lock(_tasks)

   // The maximum concurrency level allowed by this scheduler. 
   private readonly int _maxDegreeOfParallelism;

   // Indicates whether the scheduler is currently processing work items. 
   private int _delegatesQueuedOrRunning = 0;

   // Creates a new instance with the specified degree of parallelism. 
   public LimitedConcurrencyLevelTaskScheduler(int maxDegreeOfParallelism)
   {
       if (maxDegreeOfParallelism < 1) throw new ArgumentOutOfRangeException("maxDegreeOfParallelism");
       _maxDegreeOfParallelism = maxDegreeOfParallelism;
   }

   // Queues a task to the scheduler. 
   protected sealed override void QueueTask(Task task)
   {
      // Add the task to the list of tasks to be processed.  If there aren't enough 
      // delegates currently queued or running to process tasks, schedule another. 
       lock (_tasks)
       {
           _tasks.AddLast(task);
           if (_delegatesQueuedOrRunning < _maxDegreeOfParallelism)
           {
               ++_delegatesQueuedOrRunning;
               NotifyThreadPoolOfPendingWork();
           }
       }
   }

   // Inform the ThreadPool that there's work to be executed for this scheduler. 
   private void NotifyThreadPoolOfPendingWork()
   {
       ThreadPool.UnsafeQueueUserWorkItem(_ =>
       {
           // Note that the current thread is now processing work items.
           // This is necessary to enable inlining of tasks into this thread.
           _currentThreadIsProcessingItems = true;
           try
           {
               // Process all available items in the queue.
               while (true)
               {
                   Task item;
                   lock (_tasks)
                   {
                       // When there are no more items to be processed,
                       // note that we're done processing, and get out.
                       if (_tasks.Count == 0)
                       {
                           --_delegatesQueuedOrRunning;
                           break;
                       }

                       // Get the next item from the queue
                       item = _tasks.First.Value;
                       _tasks.RemoveFirst();
                   }

                   // Execute the task we pulled out of the queue
                   base.TryExecuteTask(item);
               }
           }
           // We're done processing items on the current thread
           finally { _currentThreadIsProcessingItems = false; }
       }, null);
   }

   // Attempts to execute the specified task on the current thread. 
   protected sealed override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
   {
       // If this thread isn't already processing a task, we don't support inlining
       if (!_currentThreadIsProcessingItems) return false;

       // If the task was previously queued, remove it from the queue
       if (taskWasPreviouslyQueued) 
          // Try to run the task. 
          if (TryDequeue(task)) 
            return base.TryExecuteTask(task);
          else
             return false; 
       else 
          return base.TryExecuteTask(task);
   }

   // Attempt to remove a previously scheduled task from the scheduler. 
   protected sealed override bool TryDequeue(Task task)
   {
       lock (_tasks) return _tasks.Remove(task);
   }

   // Gets the maximum concurrency level supported by this scheduler. 
   public sealed override int MaximumConcurrencyLevel { get { return _maxDegreeOfParallelism; } }

   // Gets an enumerable of the tasks currently scheduled on this scheduler. 
   protected sealed override IEnumerable<Task> GetScheduledTasks()
   {
       bool lockTaken = false;
       try
       {
           Monitor.TryEnter(_tasks, ref lockTaken);
           if (lockTaken) return _tasks;
           else throw new NotSupportedException();
       }
       finally
       {
           if (lockTaken) Monitor.Exit(_tasks);
       }
   }
}
// The following is a portion of the output from a single run of the example:
//    'T' in task t1-4 on thread 3   'U' in task t1-4 on thread 3   'V' in task t1-4 on thread 3   
//    'W' in task t1-4 on thread 3   'X' in task t1-4 on thread 3   'Y' in task t1-4 on thread 3   
//    'Z' in task t1-4 on thread 3   '[' in task t1-4 on thread 3   '\' in task t1-4 on thread 3   
//    ']' in task t1-4 on thread 3   '^' in task t1-4 on thread 3   '_' in task t1-4 on thread 3   
//    '`' in task t1-4 on thread 3   'a' in task t1-4 on thread 3   'b' in task t1-4 on thread 3   
//    'c' in task t1-4 on thread 3   'd' in task t1-4 on thread 3   'e' in task t1-4 on thread 3   
//    'f' in task t1-4 on thread 3   'g' in task t1-4 on thread 3   'h' in task t1-4 on thread 3   
//    'i' in task t1-4 on thread 3   'j' in task t1-4 on thread 3   'k' in task t1-4 on thread 3   
//    'l' in task t1-4 on thread 3   'm' in task t1-4 on thread 3   'n' in task t1-4 on thread 3   
//    'o' in task t1-4 on thread 3   'p' in task t1-4 on thread 3   ']' in task t1-2 on thread 4   
//    '^' in task t1-2 on thread 4   '_' in task t1-2 on thread 4   '`' in task t1-2 on thread 4   
//    'a' in task t1-2 on thread 4   'b' in task t1-2 on thread 4   'c' in task t1-2 on thread 4   
//    'd' in task t1-2 on thread 4   'e' in task t1-2 on thread 4   'f' in task t1-2 on thread 4   
//    'g' in task t1-2 on thread 4   'h' in task t1-2 on thread 4   'i' in task t1-2 on thread 4   
//    'j' in task t1-2 on thread 4   'k' in task t1-2 on thread 4   'l' in task t1-2 on thread 4   
//    'm' in task t1-2 on thread 4   'n' in task t1-2 on thread 4   'o' in task t1-2 on thread 4   
//    'p' in task t1-2 on thread 4   'q' in task t1-2 on thread 4   'r' in task t1-2 on thread 4   
//    's' in task t1-2 on thread 4   't' in task t1-2 on thread 4   'u' in task t1-2 on thread 4   
//    'v' in task t1-2 on thread 4   'w' in task t1-2 on thread 4   'x' in task t1-2 on thread 4   
//    'y' in task t1-2 on thread 4   'z' in task t1-2 on thread 4   '{' in task t1-2 on thread 4   
//    '|' in task t1-2 on thread 4   '}' in task t1-2 on thread 4   '~' in task t1-2 on thread 4   
//    'q' in task t1-4 on thread 3   'r' in task t1-4 on thread 3   's' in task t1-4 on thread 3   
//    't' in task t1-4 on thread 3   'u' in task t1-4 on thread 3   'v' in task t1-4 on thread 3   
//    'w' in task t1-4 on thread 3   'x' in task t1-4 on thread 3   'y' in task t1-4 on thread 3   
//    'z' in task t1-4 on thread 3   '{' in task t1-4 on thread 3   '|' in task t1-4 on thread 3  
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Sub Main()
      ' Create a scheduler that uses two threads. 
      Dim lcts As New LimitedConcurrencyLevelTaskScheduler(2)
      Dim tasks As New List(Of Task)()
      
      ' Create a TaskFactory and pass it our custom scheduler. 
      Dim factory As New TaskFactory(lcts)
      Dim cts As New CancellationTokenSource()
      
      ' Use our factory to run a set of tasks. 
      Dim objLock As New Object()      
      Dim outputItem As Integer 
      For tCtr As Integer = 0 To 4
         Dim iteration As Integer = tCtr
         Dim t As Task = factory.StartNew(Sub()
                                             For i As Integer = 1 To 1000
                                                SyncLock objLock
                                                   Console.Write("{0} in task t-{1} on thread {2}   ", 
                                                   i, iteration, Thread.CurrentThread.ManagedThreadId)
                                                   outputItem += 1
                                                   If outputItem Mod 3 = 0 Then Console.WriteLine()
                                                End SyncLock
                                             Next 
                                          End Sub,
                                cts.Token)
         tasks.Add(t)
      Next 
      ' Use it to run a second set of tasks.                       
      For tCtr As Integer = 0 To 4
         Dim iteration As Integer = tCtr
         Dim t1 As Task = factory.StartNew(Sub()
                                              For outer As Integer = 0 To 10
                                                 For i As Integer = &h21 To &h7E
                                                    SyncLock objLock
                                                       Console.Write("'{0}' in task t1-{1} on thread {2}   ", 
                                                                     Convert.ToChar(i), iteration, Thread.CurrentThread.ManagedThreadId)
                                                       outputItem += 1
                                                       If outputItem Mod 3 = 0 Then Console.WriteLine()
                                                    End SyncLock 
                                                 Next     
                                              Next                                           
                                           End Sub,
                                cts.Token)           
         tasks.Add(t1)
      Next
      
      ' Wait for the tasks to complete before displaying a completion message.
      Task.WaitAll(tasks.ToArray())
      cts.Dispose()
      Console.WriteLine(vbCrLf + vbCrLf + "Successful completion.")
   End Sub 
End Module

' Provides a task scheduler that ensures a maximum concurrency level while 
' running on top of the thread pool.
Public Class LimitedConcurrencyLevelTaskScheduler : Inherits TaskScheduler
   ' Indicates whether the current thread is processing work items.
   <ThreadStatic()> Private Shared _currentThreadIsProcessingItems As Boolean 
   
   ' The list of tasks to be executed 
   Private ReadOnly _tasks As LinkedList(Of Task) = New LinkedList(Of Task)() 
   
   'The maximum concurrency level allowed by this scheduler. 
   Private ReadOnly _maxDegreeOfParallelism As Integer 
   
   ' Indicates whether the scheduler is currently processing work items. 
   Private _delegatesQueuedOrRunning As Integer = 0 ' protected by lock(_tasks)
   
   ' Creates a new instance with the specified degree of parallelism. 
   Public Sub New(ByVal maxDegreeOfParallelism As Integer)
      If (maxDegreeOfParallelism < 1) Then 
         Throw New ArgumentOutOfRangeException("maxDegreeOfParallelism")
      End If
         _maxDegreeOfParallelism = maxDegreeOfParallelism
   End Sub 

   ' Queues a task to the scheduler. 
   Protected Overrides Sub QueueTask(ByVal t As Task)
      ' Add the task to the list of tasks to be processed.  If there aren't enough 
      ' delegates currently queued or running to process tasks, schedule another. 
      SyncLock (_tasks)
         _tasks.AddLast(t)
         If (_delegatesQueuedOrRunning < _maxDegreeOfParallelism) Then
            _delegatesQueuedOrRunning = _delegatesQueuedOrRunning + 1
            NotifyThreadPoolOfPendingWork()
         End If 
      End SyncLock 
   End Sub 
   
   ' Inform the ThreadPool that there's work to be executed for this scheduler. 
   Private Sub NotifyThreadPoolOfPendingWork()
   
      ThreadPool.UnsafeQueueUserWorkItem(Sub()
                                            ' Note that the current thread is now processing work items. 
                                            ' This is necessary to enable inlining of tasks into this thread.
                                            _currentThreadIsProcessingItems = True 
                                            Try 
                                               ' Process all available items in the queue. 
                                               While (True)
                                                  Dim item As Task
                                                  SyncLock (_tasks)
                                                     ' When there are no more items to be processed, 
                                                     ' note that we're done processing, and get out. 
                                                     If (_tasks.Count = 0) Then
                                                        _delegatesQueuedOrRunning = _delegatesQueuedOrRunning - 1
                                                        Exit While 
                                                     End If 
   
                                                     ' Get the next item from the queue
                                                     item = _tasks.First.Value
                                                     _tasks.RemoveFirst()
                                                  End SyncLock 
   
                                                  ' Execute the task we pulled out of the queue 
                                                  MyBase.TryExecuteTask(item)
                                               End While 
                                               ' We're done processing items on the current thread 
                                            Finally
                                               _currentThreadIsProcessingItems = False 
                                            End Try 
                                         End Sub,
                                    Nothing)
   End Sub 
   
   ' Attempts to execute the specified task on the current thread. 
   Protected Overrides Function TryExecuteTaskInline(ByVal t As Task, 
                                                     ByVal taskWasPreviouslyQueued As Boolean) As Boolean 
      ' If this thread isn't already processing a task, we don't support inlining 
      If (Not _currentThreadIsProcessingItems) Then 
         Return False 
      End If 
   
      ' If the task was previously queued, remove it from the queue 
      If (taskWasPreviouslyQueued) Then
         ' Try to run the task. 
         If TryDequeue(t) Then 
            Return MyBase.TryExecuteTask(t)
         Else
            Return False 
         End If     
      Else 
         Return MyBase.TryExecuteTask(t)
      End If   
   End Function 
   
   ' Attempt to remove a previously scheduled task from the scheduler. 
   Protected Overrides Function TryDequeue(ByVal t As Task) As Boolean 
      SyncLock (_tasks)
         Return _tasks.Remove(t)
      End SyncLock 
   End Function 
   
   ' Gets the maximum concurrency level supported by this scheduler. 
   Public Overrides ReadOnly Property MaximumConcurrencyLevel As Integer 
      Get 
         Return _maxDegreeOfParallelism
      End Get 
   End Property 
   
   ' Gets an enumerable of the tasks currently scheduled on this scheduler. 
   Protected Overrides Function GetScheduledTasks() As IEnumerable(Of Task)
      Dim lockTaken As Boolean = False 
      Try
         Monitor.TryEnter(_tasks, lockTaken)
         If (lockTaken) Then 
            Return _tasks.ToArray()
         Else 
            Throw New NotSupportedException()
         End If 
      Finally 
         If (lockTaken) Then
            Monitor.Exit(_tasks)
         End If 
      End Try 
   End Function 
End Class 
' The following is a portion of the output from a single run of the example:
'    'T' in task t1-4 on thread 3   'U' in task t1-4 on thread 3   'V' in task t1-4 on thread 3   
'    'W' in task t1-4 on thread 3   'X' in task t1-4 on thread 3   'Y' in task t1-4 on thread 3   
'    'Z' in task t1-4 on thread 3   '[' in task t1-4 on thread 3   '\' in task t1-4 on thread 3   
'    ']' in task t1-4 on thread 3   '^' in task t1-4 on thread 3   '_' in task t1-4 on thread 3   
'    '`' in task t1-4 on thread 3   'a' in task t1-4 on thread 3   'b' in task t1-4 on thread 3   
'    'c' in task t1-4 on thread 3   'd' in task t1-4 on thread 3   'e' in task t1-4 on thread 3   
'    'f' in task t1-4 on thread 3   'g' in task t1-4 on thread 3   'h' in task t1-4 on thread 3   
'    'i' in task t1-4 on thread 3   'j' in task t1-4 on thread 3   'k' in task t1-4 on thread 3   
'    'l' in task t1-4 on thread 3   'm' in task t1-4 on thread 3   'n' in task t1-4 on thread 3   
'    'o' in task t1-4 on thread 3   'p' in task t1-4 on thread 3   ']' in task t1-2 on thread 4   
'    '^' in task t1-2 on thread 4   '_' in task t1-2 on thread 4   '`' in task t1-2 on thread 4   
'    'a' in task t1-2 on thread 4   'b' in task t1-2 on thread 4   'c' in task t1-2 on thread 4   
'    'd' in task t1-2 on thread 4   'e' in task t1-2 on thread 4   'f' in task t1-2 on thread 4   
'    'g' in task t1-2 on thread 4   'h' in task t1-2 on thread 4   'i' in task t1-2 on thread 4   
'    'j' in task t1-2 on thread 4   'k' in task t1-2 on thread 4   'l' in task t1-2 on thread 4   
'    'm' in task t1-2 on thread 4   'n' in task t1-2 on thread 4   'o' in task t1-2 on thread 4   
'    'p' in task t1-2 on thread 4   'q' in task t1-2 on thread 4   'r' in task t1-2 on thread 4   
'    's' in task t1-2 on thread 4   't' in task t1-2 on thread 4   'u' in task t1-2 on thread 4   
'    'v' in task t1-2 on thread 4   'w' in task t1-2 on thread 4   'x' in task t1-2 on thread 4   
'    'y' in task t1-2 on thread 4   'z' in task t1-2 on thread 4   '{' in task t1-2 on thread 4   
'    '|' in task t1-2 on thread 4   '}' in task t1-2 on thread 4   '~' in task t1-2 on thread 4   
'    'q' in task t1-4 on thread 3   'r' in task t1-4 on thread 3   's' in task t1-4 on thread 3   
'    't' in task t1-4 on thread 3   'u' in task t1-4 on thread 3   'v' in task t1-4 on thread 3   
'    'w' in task t1-4 on thread 3   'x' in task t1-4 on thread 3   'y' in task t1-4 on thread 3   
'    'z' in task t1-4 on thread 3   '{' in task t1-4 on thread 3   '|' in task t1-4 on thread 3  

In Code Gallery sono inoltre disponibili diverse utilità di pianificazione delle attività di esempio: Esempi per la programmazione parallela con il .NET Framework 4.In addition, several sample task schedulers are available on Code Gallery: Samples for Parallel Programming with the .NET Framework 4.

Commenti

Un'istanza della TaskScheduler classe rappresenta un'utilità di pianificazione.An instance of the TaskScheduler class represents a task scheduler. Un'utilità di pianificazione assicura che il lavoro di un'attività viene eseguito.A task scheduler ensures that the work of a task is eventually executed.

L'utilità di pianificazione predefinita si basa su pool di thread .NET Framework 4, che fornisce l'acquisizione del lavoro per il bilanciamento del carico, l'aggiunta/ritiro dei thread per la velocità effettiva massima e buone prestazioni complessive.The default task scheduler is based on the .NET Framework 4 thread pool, which provides work-stealing for load-balancing, thread injection/retirement for maximum throughput, and overall good performance. Dovrebbe essere sufficiente per la maggior parte degli scenari.It should be sufficient for most scenarios.

La TaskScheduler classe funge anche da punto di estensione per tutta la logica di pianificazione personalizzabile.The TaskScheduler class also serves as the extension point for all customizable scheduling logic. Sono inclusi meccanismi come la pianificazione di un'attività per l'esecuzione e il modo in cui le attività pianificate devono essere esposte ai debugger.This includes mechanisms such as how to schedule a task for execution, and how scheduled tasks should be exposed to debuggers. Se sono necessarie funzionalità speciali, è possibile creare un'utilità di pianificazione personalizzata e abilitarla per attività o query specifiche.If you require special functionality, you can create a custom scheduler and enable it for specific tasks or queries.

In questo argomentoIn this topic:
L'utilità di pianificazione predefinita e il pool di threadThe default task scheduler and the thread pool
Coda globale e code localiThe global queue vs. local queues
Furto di lavoroWork stealing
Attività a esecuzione prolungataLong-running tasks
Incorporamento attivitàTask inlining
Specifica di un contesto di sincronizzazioneSpecifying a synchronization context

L'utilità di pianificazione predefinita e il pool di threadThe default task scheduler and the thread pool

L'utilità di pianificazione predefinita per il Task Parallel Library e PLINQ utilizza il pool di thread .NET Framework, rappresentato dalla ThreadPool classe, per accodare ed eseguire il lavoro.The default scheduler for the Task Parallel Library and PLINQ uses the .NET Framework thread pool, which is represented by the ThreadPool class, to queue and execute work. Il pool di thread usa le informazioni fornite dal Task tipo per supportare in modo efficiente il parallelismo con granularità fine (unità di lavoro di breve durata) che spesso rappresentano le attività e le query in parallelo.The thread pool uses the information that is provided by the Task type to efficiently support the fine-grained parallelism (short-lived units of work) that parallel tasks and queries often represent.

Coda globale e code localiThe global queue vs. local queues

Il pool di thread mantiene una coda di lavoro FIFO (First-in, First-out) globale per i thread in ogni dominio applicazione.The thread pool maintains a global FIFO (first-in, first-out) work queue for threads in each application domain. Ogni volta che un programma ThreadPool.QueueUserWorkItem chiama il ThreadPool.UnsafeQueueUserWorkItemmetodo (o), il lavoro viene inserito in questa coda condivisa e infine rimosso dalla coda nel thread successivo che diventa disponibile.Whenever a program calls the ThreadPool.QueueUserWorkItem (or ThreadPool.UnsafeQueueUserWorkItem) method, the work is put on this shared queue and eventually de-queued onto the next thread that becomes available. A partire da .NET Framework 4, questa coda è stata migliorata in modo da usare un algoritmo senza blocco simile alla ConcurrentQueue<T> classe.Starting with the .NET Framework 4, this queue has been improved to use a lock-free algorithm that resembles the ConcurrentQueue<T> class. Utilizzando questa implementazione senza blocco, il pool di thread impiega meno tempo quando Accoda e Annulla la coda degli elementi di lavoro.By using this lock-free implementation, the thread pool spends less time when it queues and de-queues work items. Questo vantaggio in merito alle prestazioni è disponibile per tutti i programmi che utilizzano il pool di thread.This performance benefit is available to all programs that use the thread pool.

Le attività di primo livello, ovvero quelle non create nell'ambito di un'altra attività, vengono inserite nella coda globale come qualsiasi altro elemento di lavoro.Top-level tasks, which are tasks that are not created in the context of another task, are put on the global queue just like any other work item. Tuttavia le attività annidate o figlio, create nell'ambito di un'altra attività, vengono gestite in modo molto diverso.However, nested or child tasks, which are created in the context of another task, are handled quite differently. Un'attività figlio o annidata viene inserita in una coda locale specifica del thread in cui è in esecuzione l'attività padre.A child or nested task is put on a local queue that is specific to the thread on which the parent task is executing. L'attività padre può essere un'attività di primo livello o anche l'elemento figlio di un'altra attività.The parent task may be a top-level task or it also may be the child of another task. Quando questo thread è disponibile per altro lavoro, esegue innanzitutto una ricerca nella coda locale.When this thread is ready for more work, it first looks in the local queue. Se sono presenti elementi di lavoro in attesa, è possibile accedervi rapidamente.If work items are waiting there, they can be accessed quickly. È possibile accedere alle code locali in ordine LIFO (Last-in, First-out) per mantenere la località della cache e ridurre i conflitti.The local queues are accessed in last-in, first-out order (LIFO) to preserve cache locality and reduce contention. Per ulteriori informazioni sulle attività figlio e le attività nidificate, vedere attività figlio connesse e scollegate.For more information about child tasks and nested tasks, see Attached and Detached Child Tasks.

L'uso di code locali non solo riduce la pressione sulla coda globale, ma sfrutta anche la località dei dati.The use of local queues not only reduces pressure on the global queue, but also takes advantage of data locality. Gli elementi di lavoro nella coda locale fanno spesso riferimento a strutture di dati fisicamente vicine le une alle altre in memoria.Work items in the local queue frequently reference data structures that are physically near one another in memory. In questi casi, i dati sono già presenti nella cache dopo l'esecuzione della prima attività e sono accessibili rapidamente.In these cases, the data is already in the cache after the first task has run and can be accessed quickly. Parallel LINQ (PLINQ) e la classe Parallel utilizzano le attività annidate e le attività figlio in maniera estensiva e raggiungono velocità di aumento significative usando le code di lavoro locali.Both Parallel LINQ (PLINQ) and the Parallel class use nested tasks and child tasks extensively, and achieve significant speedups by using the local work queues.

Furto di lavoroWork stealing

A partire da .NET Framework 4, il pool di thread include anche un algoritmo di acquisizione del lavoro per garantire che nessun thread sia inattivo mentre altri ancora lavorano nelle code.Starting with the .NET Framework 4, the thread pool also features a work-stealing algorithm to help make sure that no threads are sitting idle while others still have work in their queues. Quando un thread del pool di thread è disponibile per altro lavoro, effettua prima una ricerca all'inizio della propria coda locale, quindi nella coda globale e infine nelle code locali degli altri thread.When a thread-pool thread is ready for more work, it first looks at the head of its local queue, then in the global queue, and then in the local queues of other threads. Se trova un elemento di lavoro nella coda locale di un altro thread, prima applica l'euristica per avere la certezza di poter eseguire il lavoro in modo efficiente.If it finds a work item in the local queue of another thread, it first applies heuristics to make sure that it can run the work efficiently. In tal caso, Annulla l'accodamento dell'elemento di lavoro dalla coda (in ordine FIFO).If it can, it de-queues the work item from the tail (in FIFO order). In questo modo viene ridotto il conflitto in ogni coda locale e viene mantenuta la località dei dati.This reduces contention on each local queue and preserves data locality. Questa architettura consente al pool di thread di bilanciare il carico di lavoro in modo più efficiente rispetto alle versioni precedenti.This architecture helps the thread pool load-balance work more efficiently than past versions did.

Attività a esecuzione prolungataLong-running tasks

Può essere opportuno impedire in modo esplicito l'inserimento di un'attività in una coda locale.You may want to explicitly prevent a task from being put on a local queue. Ad esempio, si potrebbe sapere che un particolare elemento di lavoro verrà eseguito per un tempo relativamente lungo e probabilmente bloccherà tutti gli altri elementi di lavoro nella coda locale.For example, you may know that a particular work item will run for a relatively long time and is likely to block all other work items on the local queue. In questo caso, è possibile specificare l'opzione System.Threading.Tasks.TaskCreationOptions, che fornisce all'utilità di pianificazione il suggerimento che per l'attività potrebbe essere necessario un altro thread in modo che non blocchi l'avanzamento di altri thread o elementi di lavoro nella coda locale.In this case, you can specify the System.Threading.Tasks.TaskCreationOptions option, which provides a hint to the scheduler that an additional thread might be required for the task so that it does not block the forward progress of other threads or work items on the local queue. Utilizzando questa opzione è possibile evitare completamente il pool di thread, incluse le code globali e locali.By using this option you avoid the thread pool completely, including the global and local queues.

Incorporamento attivitàTask inlining

In alcuni casi, quando Task un oggetto è in attesa, può essere eseguito in modo sincrono sul thread che esegue l'operazione di attesa.In some cases when a Task is waited on, it may be executed synchronously on the thread that is performing the wait operation. Ciò consente di migliorare le prestazioni evitando la necessità di un thread aggiuntivo e usando invece il thread esistente, che altrimenti sarebbe stato bloccato.This enhances performance by preventing the need for an additional thread and instead using the existing thread, which would have blocked otherwise. Per evitare errori dovuti alla rientranza, l'inline dell'attività si verifica solo quando la destinazione di attesa viene trovata nella coda locale del thread pertinente.To prevent errors due to reentrancy, task inlining only occurs when the wait target is found in the relevant thread's local queue.

Specifica di un contesto di sincronizzazioneSpecifying a synchronization context

È possibile usare il metodo TaskScheduler.FromCurrentSynchronizationContext per specificare che è necessario pianificare l'esecuzione di un'attività in un particolare thread.You can use the TaskScheduler.FromCurrentSynchronizationContext method to specify that a task should be scheduled to run on a particular thread. Ciò risulta utile in framework come Windows Form e Windows Presentation Foundation dove l'accesso agli oggetti dell'interfaccia utente è spesso limitato alla coda in esecuzione nello stesso thread in cui è stato creato l'oggetto dell'interfaccia utente.This is useful in frameworks such as Windows Forms and Windows Presentation Foundation where access to user interface objects is often restricted to code that is running on the same thread on which the UI object was created.

Nell'esempio seguente viene usato TaskScheduler.FromCurrentSynchronizationContext il metodo in un'app Windows Presentation Foundation (WPF) per pianificare un'attività sullo stesso thread in cui è stato creato il controllo dell'interfaccia utente.The following example uses the TaskScheduler.FromCurrentSynchronizationContext method in a Windows Presentation Foundation (WPF) app to schedule a task on the same thread that the user interface (UI) control was created on. Nell'esempio viene creato un mosaico di immagini selezionate in modo casuale da una directory specificata.The example creates a mosaic of images that are randomly selected from a specified directory. Gli oggetti WPF vengono utilizzati per caricare e ridimensionare le immagini.The WPF objects are used to load and resize the images. I pixel non elaborati vengono quindi passati a un'attività che For usa un ciclo per scrivere i dati pixel in una matrice a byte singolo di grandi dimensioni.The raw pixels are then passed to a task that uses a For loop to write the pixel data into a large single-byte array. Non è necessaria alcuna sincronizzazione perché due riquadri occupano gli stessi elementi della matrice.No synchronization is required because no two tiles occupy the same array elements. I riquadri possono anche essere scritti in qualsiasi ordine, perché la loro posizione viene calcolata indipendentemente da qualsiasi altro riquadro.The tiles can also be written in any order because their position is calculated independently of any other tile. La matrice di grandi dimensioni viene quindi passata a un'attività che viene eseguita sul thread dell'interfaccia utente, in cui i dati pixel vengono caricati in un controllo immagine.The large array is then passed to a task that runs on the UI thread, where the pixel data is loaded into an Image control.

L'esempio sposta i dati dal thread dell'interfaccia utente, li modifica usando gli oggetti Task e i cicli paralleli e quindi li passa nuovamente a un'attività che viene eseguita nel thread dell'interfaccia utente.The example moves data off the UI thread, modifies it by using parallel loops and Task objects, and then passes it back to a task that runs on the UI thread. Questo approccio è utile quando è necessario utilizzare il Task Parallel Library per eseguire operazioni che non sono supportate dall'API WPF o che non sono sufficientemente veloci.This approach is useful when you have to use the Task Parallel Library to perform operations that either are not supported by the WPF API, or are not sufficiently fast. Un altro modo per creare un mosaico di immagini in WPF consiste nell' System.Windows.Controls.WrapPanel usare un controllo e aggiungervi immagini.Another way to create an image mosaic in WPF is to use a System.Windows.Controls.WrapPanel control and add images to it. WrapPanel Gestisce il lavoro di posizionamento dei riquadri.The WrapPanel handles the work of positioning the tiles. Tuttavia, questa operazione può essere eseguita solo sul thread dell'interfaccia utente.However, this work can only be performed on the UI thread.

using System;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace WPF_CS1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private int fileCount;
        int colCount;
        int rowCount;
        private int tilePixelHeight;
        private int tilePixelWidth;
        private int largeImagePixelHeight;
        private int largeImagePixelWidth;
        private int largeImageStride;
        PixelFormat format;
        BitmapPalette palette = null;

        public MainWindow()
        {
            InitializeComponent();

            // For this example, values are hard-coded to a mosaic of 8x8 tiles.
            // Each tile is 50 pixels high and 66 pixels wide and 32 bits per pixel.
            colCount = 12;
            rowCount = 8;
            tilePixelHeight = 50;
            tilePixelWidth = 66;
            largeImagePixelHeight = tilePixelHeight * rowCount;
            largeImagePixelWidth = tilePixelWidth * colCount;
            largeImageStride = largeImagePixelWidth * (32 / 8);
            this.Width = largeImagePixelWidth + 40;
            image.Width = largeImagePixelWidth;
            image.Height = largeImagePixelHeight;


        }

        private void button_Click(object sender, RoutedEventArgs e)
        {

            // For best results use 1024 x 768 jpg files at 32bpp.
            string[] files = System.IO.Directory.GetFiles(@"C:\Users\Public\Pictures\Sample Pictures\", "*.jpg");

            fileCount = files.Length;
            Task<byte[]>[] images = new Task<byte[]>[fileCount];
            for (int i = 0; i < fileCount; i++)
            {
                int x = i;
                images[x] = Task.Factory.StartNew(() => LoadImage(files[x]));
            }

            // When they've all been loaded, tile them into a single byte array.
            var tiledImage = Task.Factory.ContinueWhenAll(
                images, (i) => TileImages(i));

            // We are currently on the UI thread. Save the sync context and pass it to
            // the next task so that it can access the UI control "image".
            var UISyncContext = TaskScheduler.FromCurrentSynchronizationContext();

            // On the UI thread, put the bytes into a bitmap and
            // display it in the Image control.
            var t3 = tiledImage.ContinueWith((antecedent) =>
            {
                // Get System DPI.
                Matrix m = PresentationSource.FromVisual(Application.Current.MainWindow)
                                            .CompositionTarget.TransformToDevice;
                double dpiX = m.M11;
                double dpiY = m.M22;

                BitmapSource bms = BitmapSource.Create(largeImagePixelWidth,
                    largeImagePixelHeight,
                    dpiX,
                    dpiY,
                    format,
                    palette, //use default palette
                    antecedent.Result,
                    largeImageStride);
                image.Source = bms;
            }, UISyncContext);
        }

        byte[] LoadImage(string filename)
        {
            // Use the WPF BitmapImage class to load and 
            // resize the bitmap. NOTE: Only 32bpp formats are supported correctly.
            // Support for additional color formats is left as an exercise
            // for the reader. For more information, see documentation for ColorConvertedBitmap.

            BitmapImage bitmapImage = new BitmapImage();
            bitmapImage.BeginInit();
            bitmapImage.UriSource = new Uri(filename);
            bitmapImage.DecodePixelHeight = tilePixelHeight;
            bitmapImage.DecodePixelWidth = tilePixelWidth;
            bitmapImage.EndInit();

            format = bitmapImage.Format;
            int size = (int)(bitmapImage.Height * bitmapImage.Width);
            int stride = (int)bitmapImage.Width * 4;
            byte[] dest = new byte[stride * tilePixelHeight];

            bitmapImage.CopyPixels(dest, stride, 0);

            return dest;
        }

        int Stride(int pixelWidth, int bitsPerPixel)
        {
            return (((pixelWidth * bitsPerPixel + 31) / 32) * 4);
        }

        // Map the individual image tiles to the large image
        // in parallel. Any kind of raw image manipulation can be
        // done here because we are not attempting to access any 
        // WPF controls from multiple threads.
        byte[] TileImages(Task<byte[]>[] sourceImages)
        {
            byte[] largeImage = new byte[largeImagePixelHeight * largeImageStride];
            int tileImageStride = tilePixelWidth * 4; // hard coded to 32bpp

            Random rand = new Random();
            Parallel.For(0, rowCount * colCount, (i) =>
            {
                // Pick one of the images at random for this tile.
                int cur = rand.Next(0, sourceImages.Length);
                byte[] pixels = sourceImages[cur].Result;

                // Get the starting index for this tile.
                int row = i / colCount;
                int col = (int)(i % colCount);
                int idx = ((row * (largeImageStride * tilePixelHeight)) + (col * tileImageStride));

                // Write the pixels for the current tile. The pixels are not contiguous
                // in the array, therefore we have to advance the index by the image stride
                // (minus the stride of the tile) for each scanline of the tile.
                int tileImageIndex = 0;
                for (int j = 0; j < tilePixelHeight; j++)
                {
                    // Write the next scanline for this tile.
                    for (int k = 0; k < tileImageStride; k++)
                    {
                        largeImage[idx++] = pixels[tileImageIndex++];
                    }
                    // Advance to the beginning of the next scanline.
                    idx += largeImageStride - tileImageStride;
                }
            });
            return largeImage;
        }
    }
}
Imports System.Threading.Tasks
Imports System.Windows
Imports System.Windows.Media
Imports System.Windows.Media.Imaging

Partial Public Class MainWindow : Inherits Window
    Dim fileCount As Integer
    Dim colCount As Integer
    Dim rowCount As Integer
    Dim tilePixelHeight As Integer
    Dim tilePixelWidth As Integer
    Dim largeImagePixelHeight As Integer
    Dim largeImagePixelWidth As Integer
    Dim largeImageStride As Integer
    Dim format As PixelFormat
    Dim palette As BitmapPalette = Nothing

    Public Sub New()
        InitializeComponent()

        ' For this example, values are hard-coded to a mosaic of 8x8 tiles.
        ' Each tile Is 50 pixels high and 66 pixels wide and 32 bits per pixel.
        colCount = 12
        rowCount = 8
        tilePixelHeight = 50
        tilePixelWidth = 66
        largeImagePixelHeight = tilePixelHeight * rowCount
        largeImagePixelWidth = tilePixelWidth * colCount
        largeImageStride = largeImagePixelWidth * (32 / 8)
        Me.Width = largeImagePixelWidth + 40
        image.Width = largeImagePixelWidth
        image.Height = largeImagePixelHeight
    End Sub

    Private Sub button_Click(sender As Object, e As RoutedEventArgs) _
        Handles button.Click

        ' For best results use 1024 x 768 jpg files at 32bpp.
        Dim files() As String = System.IO.Directory.GetFiles("C:\Users\Public\Pictures\Sample Pictures\", "*.jpg")

        fileCount = files.Length
        Dim images(fileCount - 1) As Task(Of Byte())
        For i As Integer = 0 To fileCount - 1
            Dim x As Integer = i
            images(x) = Task.Factory.StartNew(Function() LoadImage(files(x)))
        Next

        ' When they have all been loaded, tile them into a single byte array.
        'var tiledImage = Task.Factory.ContinueWhenAll(
        '        images, (i) >= TileImages(i));

        '        Dim tiledImage As Task(Of Byte()) = Task.Factory.ContinueWhenAll(images, Function(i As Task(Of Byte())) TileImages(i))
        Dim tiledImage = Task.Factory.ContinueWhenAll(images, Function(i As Task(Of Byte())()) TileImages(i))
        ' We are currently on the UI thread. Save the sync context and pass it to
        ' the next task so that it can access the UI control "image1".
        Dim UISyncContext = TaskScheduler.FromCurrentSynchronizationContext()

        ' On the UI thread, put the bytes into a bitmap and
        ' display it in the Image control.
        Dim t3 = tiledImage.ContinueWith(Sub(antecedent)
                                             ' Get System DPI.
                                             Dim m As Matrix = PresentationSource.FromVisual(Application.Current.MainWindow).CompositionTarget.TransformToDevice
                                             Dim dpiX As Double = m.M11
                                             Dim dpiY As Double = m.M22

                                             ' Use the default palette in creating the bitmap.
                                             Dim bms As BitmapSource = BitmapSource.Create(largeImagePixelWidth,
                                                                                           largeImagePixelHeight,
                                             dpiX,
                                             dpiY,
                                             format,
                                             palette,
                                             antecedent.Result,
                                             largeImageStride)
                                             image.Source = bms
                                         End Sub, UISyncContext)
    End Sub

    Public Function LoadImage(filename As String) As Byte()
        ' Use the WPF BitmapImage class to load and 
        ' resize the bitmap. NOTE: Only 32bpp formats are supported correctly.
        ' Support for additional color formats Is left as an exercise
        ' for the reader. For more information, see documentation for ColorConvertedBitmap.
        Dim bitmapImage As New BitmapImage()
        bitmapImage.BeginInit()
        bitmapImage.UriSource = New Uri(filename)
        bitmapImage.DecodePixelHeight = tilePixelHeight
        bitmapImage.DecodePixelWidth = tilePixelWidth
        bitmapImage.EndInit()

        format = bitmapImage.Format
        Dim size As Integer = CInt(bitmapImage.Height * bitmapImage.Width)
        Dim stride As Integer = CInt(bitmapImage.Width * 4)
        Dim dest(stride * tilePixelHeight - 1) As Byte

        bitmapImage.CopyPixels(dest, stride, 0)

        Return dest
    End Function

    Function Stride(pixelWidth As Integer, bitsPerPixel As Integer) As Integer
        Return (((pixelWidth * bitsPerPixel + 31) / 32) * 4)
    End Function

    ' Map the individual image tiles to the large image
    ' in parallel. Any kind of raw image manipulation can be
    ' done here because we are Not attempting to access any 
    ' WPF controls from multiple threads.
    Function TileImages(sourceImages As Task(Of Byte())()) As Byte()
        Dim largeImage(largeImagePixelHeight * largeImageStride - 1) As Byte
        Dim tileImageStride As Integer = tilePixelWidth * 4 ' hard coded To 32bpp

        Dim rand As New Random()
        Parallel.For(0, rowCount * colCount, Sub(i)
                                                 ' Pick one of the images at random for this tile.
                                                 Dim cur As Integer = rand.Next(0, sourceImages.Length)
                                                 Dim pixels() As Byte = sourceImages(cur).Result

                                                 ' Get the starting index for this tile.
                                                 Dim row As Integer = i \ colCount
                                                 Dim col As Integer = i Mod colCount
                                                 Dim idx As Integer = ((row * (largeImageStride * tilePixelHeight)) + (col * tileImageStride))

                                                 ' Write the pixels for the current tile. The pixels are Not contiguous
                                                 ' in the array, therefore we have to advance the index by the image stride
                                                 ' (minus the stride of the tile) for each scanline of the tile.
                                                 Dim tileImageIndex As Integer = 0
                                                 For j As Integer = 0 To tilePixelHeight - 1
                                                     ' Write the next scanline for this tile.
                                                     For k As Integer = 0 To tileImageStride - 1
                                                         largeImage(idx) = pixels(tileImageIndex)
                                                         idx += 1
                                                         tileImageIndex += 1
                                                     Next
                                                     ' Advance to the beginning of the next scanline.
                                                     idx += largeImageStride - tileImageStride
                                                 Next
                                             End Sub)
        Return largeImage
    End Function
End Class

Per creare l'esempio, creare un progetto di applicazione WPF in Visual Studio e denominarlo WPF_CS1 ( C# per un progetto WPF) o WPF_VB1 (per un Visual Basic progetto WPF).To create the example, create a WPF application project in Visual Studio and name it WPF_CS1 (for a C# WPF project) or WPF_VB1 (for a Visual Basic WPF project). Eseguire quindi le operazioni seguenti:Then do the following:

  1. In visualizzazione progettazione trascinare un Image controllo dalla casella degli strumenti nell'angolo superiore sinistro dell'area di progettazione.In design view, drag an Image control from the Toolbox onto the upper left corner of the design surface. Nella casella di testo nome della finestra Proprietà assegnare al controllo il nome "immagine".In the Name textbox of the Properties window, name the control "image".

  2. Trascinare un Button controllo dalla casella degli strumenti nella parte inferiore sinistra della finestra dell'applicazione.Drag a Button control from the Toolbox to the lower left part of the application window. Nella visualizzazione XAML specificare la Content proprietà del pulsante come "make a Mosaic" e Width specificarne la proprietà come "100".In XAML view, specify the Content property of the button as "Make a mosaic", and specify its Width property as "100". Connettere l' Click button_Click evento al gestore eventi definito nel <Button> codice dell'esempio aggiungendo Click="button_Click" all'elemento.Connect the Click event with the button_Click event handler defined in the example's code by adding Click="button_Click" to the <Button> element. Nella casella di testo nome della finestra Proprietà , denominare il controllo "button".In the Name textbox of the Properties window, name the control "button".

  3. Sostituire l'intero contenuto del file MainWindow.xaml.cs o MainWindow. XAML. vb con il codice di questo esempio.Replace the entire contents of the MainWindow.xaml.cs or MainWindow.xaml.vb file with the code from this example. Per un C# progetto WPF, verificare che il nome dell'area di lavoro corrisponda al nome del progetto.For a C# WPF project, make sure that the name of the workspace matches the project name.

  4. L'esempio legge immagini JPEG da una directory denominata C:\Users\Public\Pictures\Sample Pictures\.The example reads JPEG images from a directory named C:\Users\Public\Pictures\Sample Pictures\. Creare la directory e inserire alcune immagini oppure modificare il percorso in modo da fare riferimento a un'altra directory che contiene immagini.Either create the directory and place some images in it, or change the path to refer to some other directory that contains images.

Questo esempio presenta alcune limitazioni.This example has some limitations. Sono supportate, ad esempio, solo le immagini 32 bit per pixel. le BitmapImage immagini in altri formati sono danneggiate dall'oggetto durante l'operazione di ridimensionamento.For example, only 32-bits-per-pixel images are supported; images in other formats are corrupted by the BitmapImage object during the resizing operation. Inoltre, le immagini di origine devono essere tutte più grandi delle dimensioni del riquadro.Also, the source images must all be larger than the tile size. Come ulteriore esercizio, è possibile aggiungere funzionalità per gestire formati di più pixel e dimensioni dei file.As a further exercise, you can add functionality to handle multiple pixel formats and file sizes.

Costruttori

TaskScheduler() TaskScheduler() TaskScheduler() TaskScheduler()

Inizializza TaskScheduler.Initializes the TaskScheduler.

Proprietà

Current Current Current Current

Ottiene l'oggetto TaskScheduler associato all'attività attualmente in esecuzione.Gets the TaskScheduler associated with the currently executing task.

Default Default Default Default

Ottiene l'istanza di TaskScheduler predefinita fornita da .NET Framework.Gets the default TaskScheduler instance that is provided by the .NET Framework.

Id Id Id Id

Ottiene l'ID univoco di questo oggetto TaskScheduler.Gets the unique ID for this TaskScheduler.

MaximumConcurrencyLevel MaximumConcurrencyLevel MaximumConcurrencyLevel MaximumConcurrencyLevel

Indica il livello di concorrenza massimo supportato da questo oggetto TaskScheduler.Indicates the maximum concurrency level this TaskScheduler is able to support.

Metodi

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determina se l'oggetto specificato è uguale all'oggetto corrente.Determines whether the specified object is equal to the current object.

(Inherited from Object)
Finalize() Finalize() Finalize() Finalize()

Libera tutte le risorse associate a questa utilità di pianificazione.Frees all resources associated with this scheduler.

FromCurrentSynchronizationContext() FromCurrentSynchronizationContext() FromCurrentSynchronizationContext() FromCurrentSynchronizationContext()

Crea un oggetto TaskScheduler associato all'oggetto SynchronizationContext corrente.Creates a TaskScheduler associated with the current SynchronizationContext.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Funge da funzione hash predefinita.Serves as the default hash function.

(Inherited from Object)
GetScheduledTasks() GetScheduledTasks() GetScheduledTasks() GetScheduledTasks()

Solo per il supporto del debugger, genera un oggetto enumerabile di istanze di Task correntemente accodate all'utilità di pianificazione in attesa di esecuzione.For debugger support only, generates an enumerable of Task instances currently queued to the scheduler waiting to be executed.

GetType() GetType() GetType() GetType()

Ottiene l'oggetto Type dell'istanza corrente.Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Crea una copia superficiale dell'oggetto Object corrente.Creates a shallow copy of the current Object.

(Inherited from Object)
QueueTask(Task) QueueTask(Task) QueueTask(Task) QueueTask(Task)

Accoda un oggetto Task all'utilità di pianificazione.Queues a Task to the scheduler.

ToString() ToString() ToString() ToString()

Restituisce una stringa che rappresenta l'oggetto corrente.Returns a string that represents the current object.

(Inherited from Object)
TryDequeue(Task) TryDequeue(Task) TryDequeue(Task) TryDequeue(Task)

Tenta di rimuovere dalla coda un oggetto Task accodato in precedenza a questa utilità di pianificazione.Attempts to dequeue a Task that was previously queued to this scheduler.

TryExecuteTask(Task) TryExecuteTask(Task) TryExecuteTask(Task) TryExecuteTask(Task)

Tenta di eseguire l'oggetto Task fornito in questa utilità di pianificazione.Attempts to execute the provided Task on this scheduler.

TryExecuteTaskInline(Task, Boolean) TryExecuteTaskInline(Task, Boolean) TryExecuteTaskInline(Task, Boolean) TryExecuteTaskInline(Task, Boolean)

Determina se l'oggetto Task fornito può essere eseguito in modo sincrono in questa chiamata e, in tal caso, lo esegue.Determines whether the provided Task can be executed synchronously in this call, and if it can, executes it.

Eventi

UnobservedTaskException UnobservedTaskException UnobservedTaskException UnobservedTaskException

Si verifica quando l'eccezione non osservata di un'attività con errori sta per attivare i criteri di escalation delle eccezioni, che per impostazione predefinita interrompono il processo.Occurs when a faulted task's unobserved exception is about to trigger exception escalation policy, which, by default, would terminate the process.

Si applica a

Thread safety

Tutti i membri del tipo TaskScheduler astratto sono thread-safe e possono essere usati contemporaneamente da più thread.All members of the abstract TaskScheduler type are thread-safe and may be used from multiple threads concurrently.

Vedi anche