ForEach(TSource) Method (Partitioner(TSource), Action(TSource, ParallelLoopState))
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Parallel.ForEach(Of TSource) Method (Partitioner(Of TSource), Action(Of TSource, ParallelLoopState))

.NET Framework 4.6 and 4.5

Executes a foreach (For Each in Visual Basic) operation on a System.Collections.Concurrent.Partitioner in which iterations may run in parallel, and the state of the loop can be monitored and manipulated.

Namespace:   System.Threading.Tasks
Assembly:  mscorlib (in mscorlib.dll)

Public Shared Function ForEach(Of TSource) (
	source As Partitioner(Of TSource),
	body As Action(Of TSource, ParallelLoopState)
) As ParallelLoopResult


Type: System.Collections.Concurrent.Partitioner(Of TSource)

The partitioner that contains the original data source.

Type: System.Action(Of TSource, ParallelLoopState)

The delegate that is invoked once per iteration.

Return Value

Type: System.Threading.Tasks.ParallelLoopResult

A structure that contains information about which portion of the loop completed.

Type Parameters


The type of the elements in source.

Exception Condition

The source argument is null.


The body argument is null.


The SupportsDynamicPartitions property in the source partitioner returns false.


A method in the source partitioner returns null.


The GetPartitions method in the source partitioner does not return the correct number of partitions.

This overload is provided for scenarios where you want to override the default partitioning scheme. For example, small loop bodies might benefit from partitioning the range. The Parallel.ForEach(Of TSource) method expects custom partitioners to support dynamic partitioning. For more information, see Custom Partitioners for PLINQ and TPL and How to: Implement Dynamic Partitions.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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