Partitioner<TSource> Class

Definition

generic <typename TSource>
public ref class Partitioner abstract

public abstract class Partitioner<TSource>

type Partitioner<'Source> = class

Public MustInherit Class Partitioner(Of TSource)

Type Parameters

Inheritance

Object

Partitioner<TSource>

Derived

System.Collections.Concurrent.OrderablePartitioner<TSource>

Examples

The following example shows how to implement a partitioner that returns a single element at a time:

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

namespace PartitionerDemo
{
 // Simple partitioner that will extract one item at a time, in a thread-safe fashion,
 // from the underlying collection.
 class SingleElementPartitioner<T> : Partitioner<T>
 {
 // The collection being wrapped by this Partitioner
 IEnumerable<T> m_referenceEnumerable;

 // Internal class that serves as a shared enumerable for the
 // underlying collection.
 private class InternalEnumerable : IEnumerable<T>, IDisposable
 {
 IEnumerator<T> m_reader;
 bool m_disposed = false;

 // These two are used to implement Dispose() when static partitioning is being performed
 int m_activeEnumerators;
 bool m_downcountEnumerators;

 // "downcountEnumerators" will be true for static partitioning, false for
 // dynamic partitioning.
 public InternalEnumerable(IEnumerator<T> reader, bool downcountEnumerators)
 {
 m_reader = reader;
 m_activeEnumerators = 0;
 m_downcountEnumerators = downcountEnumerators;
 }

 public IEnumerator<T> GetEnumerator()
 {
 if (m_disposed)
 throw new ObjectDisposedException("InternalEnumerable: Can't call GetEnumerator() after disposing");

 // For static partitioning, keep track of the number of active enumerators.
 if (m_downcountEnumerators) Interlocked.Increment(ref m_activeEnumerators);

 return new InternalEnumerator(m_reader, this);
 }

 IEnumerator IEnumerable.GetEnumerator()
 {
 return ((IEnumerable<T>)this).GetEnumerator();
 }

 public void Dispose()
 {
 if (!m_disposed)
 {
 // Only dispose the source enumerator if you are doing dynamic partitioning
 if (!m_downcountEnumerators)
 {
 m_reader.Dispose();
 }
 m_disposed = true;
 }
 }

 // Called from Dispose() method of spawned InternalEnumerator. During
 // static partitioning, the source enumerator will be automatically
 // disposed once all requested InternalEnumerators have been disposed.
 public void DisposeEnumerator()
 {
 if (m_downcountEnumerators)
 {
 if (Interlocked.Decrement(ref m_activeEnumerators) == 0)
 {
 m_reader.Dispose();
 }
 }
 }
 }

 // Internal class that serves as a shared enumerator for
 // the underlying collection.
 private class InternalEnumerator : IEnumerator<T>
 {
 T m_current;
 IEnumerator<T> m_source;
 InternalEnumerable m_controllingEnumerable;
 bool m_disposed = false;

 public InternalEnumerator(IEnumerator<T> source, InternalEnumerable controllingEnumerable)
 {
 m_source = source;
 m_current = default(T);
 m_controllingEnumerable = controllingEnumerable;
 }

 object IEnumerator.Current
 {
 get { return m_current; }
 }

 T IEnumerator<T>.Current
 {
 get { return m_current; }
 }

 void IEnumerator.Reset()
 {
 throw new NotSupportedException("Reset() not supported");
 }

 // This method is the crux of this class. Under lock, it calls
 // MoveNext() on the underlying enumerator and grabs Current.
 bool IEnumerator.MoveNext()
 {
 bool rval = false;
 lock (m_source)
 {
 rval = m_source.MoveNext();
 m_current = rval ? m_source.Current : default(T);
 }
 return rval;
 }

 void IDisposable.Dispose()
 {
 if (!m_disposed)
 {
 // Delegate to parent enumerable's DisposeEnumerator() method
 m_controllingEnumerable.DisposeEnumerator();
 m_disposed = true;
 }
 }
 }

 // Constructor just grabs the collection to wrap
 public SingleElementPartitioner(IEnumerable<T> enumerable)
 {
 // Verify that the source IEnumerable is not null
 if (enumerable == null)
 throw new ArgumentNullException("enumerable");

 m_referenceEnumerable = enumerable;
 }

 // Produces a list of "numPartitions" IEnumerators that can each be
 // used to traverse the underlying collection in a thread-safe manner.
 // This will return a static number of enumerators, as opposed to
 // GetDynamicPartitions(), the result of which can be used to produce
 // any number of enumerators.
 public override IList<IEnumerator<T>> GetPartitions(int numPartitions)
 {
 if (numPartitions < 1)
 throw new ArgumentOutOfRangeException("NumPartitions");

 List<IEnumerator<T>> list = new List<IEnumerator<T>>(numPartitions);

 // Since we are doing static partitioning, create an InternalEnumerable with reference
 // counting of spawned InternalEnumerators turned on. Once all of the spawned enumerators
 // are disposed, dynamicPartitions will be disposed.
 var dynamicPartitions = new InternalEnumerable(m_referenceEnumerable.GetEnumerator(), true);
 for (int i = 0; i < numPartitions; i++)
 list.Add(dynamicPartitions.GetEnumerator());

 return list;
 }

 // Returns an instance of our internal Enumerable class. GetEnumerator()
 // can then be called on that (multiple times) to produce shared enumerators.
 public override IEnumerable<T> GetDynamicPartitions()
 {
 // Since we are doing dynamic partitioning, create an InternalEnumerable with reference
 // counting of spawned InternalEnumerators turned off. This returned InternalEnumerable
 // will need to be explicitly disposed.
 return new InternalEnumerable(m_referenceEnumerable.GetEnumerator(), false);
 }

 // Must be set to true if GetDynamicPartitions() is supported.
 public override bool SupportsDynamicPartitions
 {
 get { return true; }
 }
 }

 class Program
 {
 // Test our SingleElementPartitioner(T) class
 static void Main()
 {
 // Our sample collection
 string[] collection = new string[] {"red", "orange", "yellow", "green", "blue", "indigo",
 "violet", "black", "white", "grey"};

 // Instantiate a partitioner for our collection
 SingleElementPartitioner<string> myPart = new SingleElementPartitioner<string>(collection);

 //
 // Simple test with ForEach
 //
 Console.WriteLine("Testing with Parallel.ForEach");
 Parallel.ForEach(myPart, item =>
 {
 Console.WriteLine(" item = {0}, thread id = {1}", item, Thread.CurrentThread.ManagedThreadId);
 });

 //
 //
 // Demonstrate the use of static partitioning, which really means
 // "using a static number of partitioners". The partitioners themselves
 // may still be "dynamic" in the sense that their outputs may not be
 // deterministic.
 //
 //

 // Perform static partitioning of collection
 var staticPartitions = myPart.GetPartitions(2);
 int index = 0;

 Console.WriteLine("Static Partitioning, 2 partitions, 2 tasks:");

 // Action will consume from static partitions
 Action staticAction = () =>
 {
 int myIndex = Interlocked.Increment(ref index) - 1; // compute your index
 var myItems = staticPartitions[myIndex]; // grab your static partition
 int id = Thread.CurrentThread.ManagedThreadId; // cache your thread id

 // Enumerate through your static partition
 while (myItems.MoveNext())
 {
 Thread.Sleep(50); // guarantees that multiple threads have a chance to run
 Console.WriteLine(" item = {0}, thread id = {1}", myItems.Current, Thread.CurrentThread.ManagedThreadId);
 }

 myItems.Dispose();
 };

 // Spawn off 2 actions to consume 2 static partitions
 Parallel.Invoke(staticAction, staticAction);

 //
 //
 // Demonstrate the use of dynamic partitioning
 //
 //

 // Grab an IEnumerable which can then be used to generate multiple
 // shared IEnumerables.
 var dynamicPartitions = myPart.GetDynamicPartitions();

 Console.WriteLine("Dynamic Partitioning, 3 tasks:");

 // Action will consume from dynamic partitions
 Action dynamicAction = () =>
 {
 // Grab an enumerator from the dynamic partitions
 var enumerator = dynamicPartitions.GetEnumerator();
 int id = Thread.CurrentThread.ManagedThreadId; // cache our thread id

 // Enumerate through your dynamic enumerator
 while (enumerator.MoveNext())
 {
 Thread.Sleep(50); // guarantees that multiple threads will have a chance to run
 Console.WriteLine(" item = {0}, thread id = {1}", enumerator.Current, id);
 }

 enumerator.Dispose();
 };

 // Spawn 3 concurrent actions to consume the dynamic partitions
 Parallel.Invoke(dynamicAction, dynamicAction, dynamicAction);

 // Clean up
 if (dynamicPartitions is IDisposable)
 ((IDisposable)dynamicPartitions).Dispose();
 }
 }
}

Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks

Module PartitionerDemo
 ' Simple partitioner that will extract one item at a time, in a thread-safe fashion,
 ' from the underlying collection.
 Class SingleElementPartitioner(Of T)
 Inherits Partitioner(Of T)
 ' The collection being wrapped by this Partitioner
 Private m_referenceEnumerable As IEnumerable(Of T)

 ' Internal class that serves as a shared enumerable for the
 ' underlying collection.
 Private Class InternalEnumerable
 Implements IEnumerable(Of T)
 Implements IDisposable

 Private m_reader As IEnumerator(Of T)
 Private m_disposed As Boolean = False

 ' These two are used to implement Dispose() when static partitioning is being performed
 Private m_activeEnumerators As Integer
 Private m_downcountEnumerators As Boolean

 ' "downcountEnumerators" will be true for static partitioning, false for
 ' dynamic partitioning. 
 Public Sub New(ByVal reader As IEnumerator(Of T), ByVal downcountEnumerators As Boolean)
 m_reader = reader
 m_activeEnumerators = 0
 m_downcountEnumerators = downcountEnumerators
 End Sub

 Public Function GetEnumerator() As IEnumerator(Of T) Implements IEnumerable(Of T).GetEnumerator
 If m_disposed Then
 Throw New ObjectDisposedException("InternalEnumerable: Can't call GetEnumerator() after disposing")
 End If

 ' For static partitioning, keep track of the number of active enumerators.
 If m_downcountEnumerators Then
 Interlocked.Increment(m_activeEnumerators)
 End If

 Return New InternalEnumerator(m_reader, Me)
 End Function

 Private Function GetEnumerator2() As IEnumerator Implements IEnumerable.GetEnumerator
 Return DirectCast(Me, IEnumerable(Of T)).GetEnumerator()
 End Function

 Public Sub Dispose() Implements IDisposable.Dispose
 If Not m_disposed Then
 ' Only dispose the source enumerator if you are doing dynamic partitioning
 If Not m_downcountEnumerators Then
 m_reader.Dispose()
 End If
 m_disposed = True
 End If
 End Sub

 ' Called from Dispose() method of spawned InternalEnumerator. During
 ' static partitioning, the source enumerator will be automatically
 ' disposed once all requested InternalEnumerators have been disposed.
 Public Sub DisposeEnumerator()
 If m_downcountEnumerators Then
 If Interlocked.Decrement(m_activeEnumerators) = 0 Then
 m_reader.Dispose()
 End If
 End If
 End Sub
 End Class

 ' Internal class that serves as a shared enumerator for 
 ' the underlying collection.
 Private Class InternalEnumerator
 Implements IEnumerator(Of T)

 Private m_current As T
 Private m_source As IEnumerator(Of T)
 Private m_controllingEnumerable As InternalEnumerable
 Private m_disposed As Boolean = False

 Public Sub New(ByVal source As IEnumerator(Of T), ByVal controllingEnumerable As InternalEnumerable)
 m_source = source
 m_current = Nothing
 m_controllingEnumerable = controllingEnumerable
 End Sub

 Private ReadOnly Property Current2() As Object Implements IEnumerator.Current
 Get
 Return m_current
 End Get
 End Property

 Private ReadOnly Property Current() As T Implements IEnumerator(Of T).Current
 Get
 Return m_current
 End Get
 End Property

 Private Sub Reset() Implements IEnumerator.Reset
 Throw New NotSupportedException("Reset() not supported")
 End Sub

 ' This method is the crux of this class. Under lock, it calls
 ' MoveNext() on the underlying enumerator and grabs Current.
 Private Function MoveNext() As Boolean Implements IEnumerator.MoveNext
 Dim rval As Boolean = False
 SyncLock m_source
 rval = m_source.MoveNext()
 m_current = If(rval, m_source.Current, Nothing)
 End SyncLock
 Return rval
 End Function

 Private Sub Dispose() Implements IDisposable.Dispose
 If Not m_disposed Then
 ' Delegate to parent enumerable's DisposeEnumerator() method
 m_controllingEnumerable.DisposeEnumerator()
 m_disposed = True
 End If
 End Sub

 End Class

 ' Constructor just grabs the collection to wrap
 Public Sub New(ByVal enumerable As IEnumerable(Of T))

 ' Verify that the source IEnumerable is not null
 If enumerable Is Nothing Then
 Throw New ArgumentNullException("enumerable")
 End If

 m_referenceEnumerable = enumerable
 End Sub

 ' Produces a list of "numPartitions" IEnumerators that can each be
 ' used to traverse the underlying collection in a thread-safe manner.
 ' This will return a static number of enumerators, as opposed to
 ' GetDynamicPartitions(), the result of which can be used to produce
 ' any number of enumerators.
 Public Overloads Overrides Function GetPartitions(ByVal numPartitions As Integer) As IList(Of IEnumerator(Of T))
 If numPartitions < 1 Then
 Throw New ArgumentOutOfRangeException("NumPartitions")
 End If

 Dim list As New List(Of IEnumerator(Of T))(numPartitions)

 ' Since we are doing static partitioning, create an InternalEnumerable with reference
 ' counting of spawned InternalEnumerators turned on. Once all of the spawned enumerators
 ' are disposed, dynamicPartitions will be disposed.
 Dim dynamicPartitions = New InternalEnumerable(m_referenceEnumerable.GetEnumerator(), True)
 For i As Integer = 0 To numPartitions - 1
 list.Add(dynamicPartitions.GetEnumerator())
 Next

 Return list
 End Function

 ' Returns an instance of our internal Enumerable class. GetEnumerator()
 ' can then be called on that (multiple times) to produce shared enumerators.
 Public Overloads Overrides Function GetDynamicPartitions() As IEnumerable(Of T)
 ' Since we are doing dynamic partitioning, create an InternalEnumerable with reference
 ' counting of spawned InternalEnumerators turned off. This returned InternalEnumerable
 ' will need to be explicitly disposed.
 Return New InternalEnumerable(m_referenceEnumerable.GetEnumerator(), False)
 End Function

 ' Must be set to true if GetDynamicPartitions() is supported.
 Public Overloads Overrides ReadOnly Property SupportsDynamicPartitions() As Boolean
 Get
 Return True
 End Get
 End Property
 End Class

 Class Program
 ' Test our SingleElementPartitioner(T) class
 Shared Sub Main()
 ' Our sample collection
 Dim collection As String() = New String() {"red", "orange", "yellow", "green", "blue", "indigo", _
 "violet", "black", "white", "grey"}

 ' Instantiate a partitioner for our collection
 Dim myPart As New SingleElementPartitioner(Of String)(Collection)

 '
 ' Simple test with ForEach
 '
 Console.WriteLine("Testing with Parallel.ForEach")
 Parallel.ForEach(myPart,
 Sub(item)
 Console.WriteLine(" item = {0}, thread id = {1}", item, Thread.CurrentThread.ManagedThreadId)
 End Sub)

 '
 '
 ' Demonstrate the use of static partitioning, which really means
 ' "using a static number of partitioners". The partitioners themselves
 ' may still be "dynamic" in the sense that their outputs may not be
 ' deterministic.
 '
 '

 ' Perform static partitioning of collection
 Dim staticPartitions = myPart.GetPartitions(2)
 Dim index As Integer = 0

 Console.WriteLine("Static Partitioning, 2 partitions, 2 tasks:")

 ' Action will consume from static partitions
 Dim staticAction As Action =
 Sub()
 Dim myIndex As Integer = Interlocked.Increment(index) - 1
 ' compute your index
 Dim myItems = staticPartitions(myIndex)
 ' grab your static partition
 Dim id As Integer = Thread.CurrentThread.ManagedThreadId
 ' cache your thread id
 ' Enumerate through your static partition
 While myItems.MoveNext()
 Thread.Sleep(50)
 ' guarantees that multiple threads have a chance to run
 Console.WriteLine(" item = {0}, thread id = {1}", myItems.Current, Thread.CurrentThread.ManagedThreadId)
 End While

 myItems.Dispose()
 End Sub

 ' Spawn off 2 actions to consume 2 static partitions
 Parallel.Invoke(staticAction, staticAction)

 '
 '
 ' Demonstrate the use of dynamic partitioning
 '
 '

 ' Grab an IEnumerable which can then be used to generate multiple
 ' shared IEnumerables.
 Dim dynamicPartitions = myPart.GetDynamicPartitions()

 Console.WriteLine("Dynamic Partitioning, 3 tasks:")

 ' Action will consume from dynamic partitions
 Dim dynamicAction As Action =
 Sub()
 ' Grab an enumerator from the dynamic partitioner
 Dim enumerator = dynamicPartitions.GetEnumerator()
 Dim id As Integer = Thread.CurrentThread.ManagedThreadId
 ' cache our thread id
 ' Enumerate through your dynamic enumerator
 While enumerator.MoveNext()
 Thread.Sleep(50)
 ' guarantees that multiple threads will have a chance to run
 Console.WriteLine(" item = {0}, thread id = {1}", enumerator.Current, id)
 End While

 enumerator.Dispose()
 End Sub

 ' Spawn 3 concurrent actions to consume the dynamic partitions
 Parallel.Invoke(dynamicAction, dynamicAction, dynamicAction)

 ' Clean up
 If TypeOf dynamicPartitions Is IDisposable Then
 DirectCast(dynamicPartitions, IDisposable).Dispose()
 End If
 End Sub
 End Class

End Module

Remarks

For more information, see Custom Partitioners for PLINQ and TPL.

Thread Safety

The static methods on Partitioner<TSource> are all thread-safe and may be used concurrently from multiple threads. However, while a created partitioner is in use, the underlying data source should not be modified, whether from the same thread that is using a partitioner or from a separate thread.

See also

• OrderablePartitioner<TSource>
• Partitioner