TaskScheduler Klas
Definitie
Belangrijk
Bepaalde informatie heeft betrekking op een voorlopige productversie die aanzienlijk kan worden gewijzigd voordat deze wordt uitgebracht. Microsoft biedt geen enkele expliciete of impliciete garanties met betrekking tot de informatie die hier wordt verstrekt.
Vertegenwoordigt een object dat het werk op laag niveau afhandelt van wachtrijtaken op threads.
public ref class TaskScheduler abstractpublic abstract class TaskSchedulertype TaskScheduler = classPublic MustInherit Class TaskScheduler- Overname
-
TaskScheduler
Voorbeelden
In het volgende voorbeeld wordt een aangepaste taakplanner gemaakt waarmee het aantal threads dat door de app wordt gebruikt, wordt beperkt. Vervolgens worden twee sets taken gestart en wordt informatie weergegeven over de taak en de thread waarop de taak wordt uitgevoerd.
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
Opmerkingen
Zie Aanvullende API-opmerkingen voor TaskScheduler voor meer informatie over deze API.
Constructors
| Name | Description |
|---|---|
| TaskScheduler() |
Initialiseert de TaskScheduler. |
Eigenschappen
| Name | Description |
|---|---|
| Current |
Hiermee haalt u de TaskScheduler gekoppelde aan de momenteel uitgevoerde taak op. |
| Default |
Hiermee haalt u de standaard-TaskScheduler-instantie op die wordt geleverd door .NET. |
| Id |
Hiermee haalt u de unieke id voor dit TaskSchedulerop. |
| MaximumConcurrencyLevel |
Geeft het maximale gelijktijdigheidsniveau aan dat kan TaskScheduler worden ondersteund. |
Methoden
| Name | Description |
|---|---|
| Equals(Object) |
Bepaalt of het opgegeven object gelijk is aan het huidige object. (Overgenomen van Object) |
| Finalize() |
Hiermee worden alle resources die aan deze planner zijn gekoppeld, vrijgemaakt. |
| FromCurrentSynchronizationContext() |
Hiermee maakt u een TaskScheduler gekoppeld aan de huidige SynchronizationContext. |
| GetHashCode() |
Fungeert als de standaardhashfunctie. (Overgenomen van Object) |
| GetScheduledTasks() |
Alleen voor foutopsporingsprogramma-ondersteuning genereert u een opsomming van Task exemplaren die momenteel in de wachtrij staan voor de planner die moet worden uitgevoerd. |
| GetType() |
Hiermee haalt u de Type huidige instantie op. (Overgenomen van Object) |
| MemberwiseClone() |
Hiermee maakt u een ondiepe kopie van de huidige Object. (Overgenomen van Object) |
| QueueTask(Task) |
Hiermee wordt een Task wachtrij naar de planner geplaatst. |
| ToString() |
Retourneert een tekenreeks die het huidige object vertegenwoordigt. (Overgenomen van Object) |
| TryDequeue(Task) |
Hiermee wordt geprobeerd een Task wachtrij op te geven die eerder in de wachtrij was geplaatst voor deze planner. |
| TryExecuteTask(Task) |
Hiermee wordt geprobeerd de opgegeven Task scheduler uit te voeren. |
| TryExecuteTaskInline(Task, Boolean) |
Bepaalt of de opgegeven Task synchroon kan worden uitgevoerd in deze aanroep en of dit wel kan, wordt deze uitgevoerd. |
gebeurtenis
| Name | Description |
|---|---|
| UnobservedTaskException |
Treedt op wanneer een foutieve uitzondering van een taak op het punt staat om escalatiebeleid voor uitzonderingen te activeren. Dit proces wordt standaard beëindigd. |
Van toepassing op
Veiligheid thread
Alle leden van het abstracte TaskScheduler type zijn thread-veilig en kunnen gelijktijdig worden gebruikt vanuit meerdere threads.