TaskScheduler Classe
Définition
Important
Certaines informations portent sur la préversion du produit qui est susceptible d’être en grande partie modifiée avant sa publication. Microsoft exclut toute garantie, expresse ou implicite, concernant les informations fournies ici.
Représente un objet qui gère les tâches de bas niveau de la mise en file d'attente de tâches sur des threads.
public ref class TaskScheduler abstractpublic abstract class TaskSchedulertype TaskScheduler = classPublic MustInherit Class TaskScheduler- Héritage
-
TaskScheduler
Exemples
L’exemple suivant crée un planificateur de tâches personnalisé qui limite le nombre de threads utilisés par l’application. Il lance ensuite deux ensembles de tâches et affiche des informations sur la tâche et le thread sur lequel la tâche s’exécute.
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
Remarques
Pour plus d’informations sur cette API, consultez Remarques supplémentaires sur l’API pour TaskScheduler.
Constructeurs
| TaskScheduler() |
Initialise la TaskScheduler. |
Propriétés
| Current |
Obtient le TaskScheduler associé à la tâche en cours d'exécution. |
| Default |
Récupère l’instance TaskScheduler par défaut fournie par .NET. |
| Id |
Obtient l'ID unique pour ce TaskScheduler. |
| MaximumConcurrencyLevel |
Indique le niveau d'accès concurrentiel maximal que ce TaskScheduler peut prendre en charge. |
Méthodes
| Equals(Object) |
Détermine si l'objet spécifié est égal à l'objet actuel. (Hérité de Object) |
| Finalize() |
Libère toutes les ressources associées à ce planificateur. |
| FromCurrentSynchronizationContext() |
Crée un TaskScheduler associé au SynchronizationContext en cours. |
| GetHashCode() |
Fait office de fonction de hachage par défaut. (Hérité de Object) |
| GetScheduledTasks() |
Pour la prise en charge du débogueur uniquement, génère un énumérateur d'instances de Task actuellement en attente d'exécution dans la file d'attente sur le planificateur. |
| GetType() |
Obtient le Type de l'instance actuelle. (Hérité de Object) |
| MemberwiseClone() |
Crée une copie superficielle du Object actuel. (Hérité de Object) |
| QueueTask(Task) |
Met en file d'attente une Task sur le planificateur. |
| ToString() |
Retourne une chaîne qui représente l'objet actuel. (Hérité de Object) |
| TryDequeue(Task) |
Tente de sortir de la file d'attente une Task qui était précédemment dans la file d'attente de ce planificateur. |
| TryExecuteTask(Task) |
Tente d'exécuter la Task fournie sur ce planificateur. |
| TryExecuteTaskInline(Task, Boolean) |
Détermine si la Task fournie peut être exécutée de façon synchrone dans cet appel et, si c'est le cas, l'exécute. |
Événements
| UnobservedTaskException |
Se produit lorsque l’exception non prise en charge d’une tâche ayant échoué est sur le point de déclencher la stratégie de promotion d’exception, qui, par défaut, arrête le processus. |
S’applique à
Cohérence de thread
Tous les membres du type abstrait TaskScheduler sont thread-safe et peuvent être utilisés à partir de plusieurs threads simultanément.
Voir aussi
Collaborer avec nous sur GitHub
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