TaskScheduler 類別
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
代表一個處理將任務排隊到執行緒的低階工作。
public ref class TaskScheduler abstractpublic abstract class TaskSchedulertype TaskScheduler = classPublic MustInherit Class TaskScheduler- 繼承
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TaskScheduler
範例
以下範例建立一個自訂任務排程器，限制應用程式使用的執行緒數量。 接著它會啟動兩組任務，並顯示有關該任務及執行緒的資訊。
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
備註
欲了解更多關於此 API 的資訊，請參閱 TaskScheduler 的補充 API 備註。
建構函式
| 名稱 | Description |
|---|---|
| TaskScheduler() |
初始化 TaskScheduler。 |
屬性
| 名稱 | Description |
|---|---|
| Current |
取得與目前執行任務相關的資料 TaskScheduler 。 |
| Default |
取得 .NET 提供的預設 TaskScheduler 實例。 |
| Id |
會取得這個 TaskScheduler唯一 ID。 |
| MaximumConcurrencyLevel |
表示該系統 TaskScheduler 能支持的最大並發等級。 |
方法
| 名稱 | Description |
|---|---|
| Equals(Object) |
判斷指定的物件是否等於目前的物件。 (繼承來源 Object) |
| Finalize() |
釋放所有與此排程器相關的資源。 |
| FromCurrentSynchronizationContext() |
會產生 TaskScheduler 與電流 SynchronizationContext相關的 。 |
| GetHashCode() |
做為預設哈希函式。 (繼承來源 Object) |
| GetScheduledTasks() |
僅支援除錯器時，會產生目前排隊等待執行的無數 Task 實例。 |
| GetType() |
取得目前實例的 Type。 (繼承來源 Object) |
| MemberwiseClone() |
建立目前 Object的淺層複本。 (繼承來源 Object) |
| QueueTask(Task) |
將 a Task 排隊到排程器。 |
| ToString() |
傳回表示目前 物件的字串。 (繼承來源 Object) |
| TryDequeue(Task) |
嘗試將先前排隊到這個排程器的 A 取消排隊 Task 。 |
| TryExecuteTask(Task) |
嘗試執行此排程器提供的 Task 服務。 |
| TryExecuteTaskInline(Task, Boolean) |
判斷所提供的 Task 是否能在此呼叫中同步執行，若能，則執行。 |
事件
| 名稱 | Description |
|---|---|
| UnobservedTaskException |
當錯誤任務的未被觀察異常即將觸發例外升級政策時，預設會終止該程序。 |
適用於
執行緒安全性
抽象型的所有成員 TaskScheduler 皆為執行緒安全，且可同時從多個執行緒使用。
