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Parallel.ForEach(TSource) Method (Partitioner(TSource), ParallelOptions, Action(TSource))

Executes a foreach (For Each in Visual Basic) operation on a Partitioner in which iterations may run in parallel and loop options can be configured.

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

static member ForEach : 
        source:Partitioner<'TSource> * 
        parallelOptions:ParallelOptions * 
        body:Action<'TSource> -> ParallelLoopResult

Type Parameters


The type of the elements in source.


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

The partitioner that contains the original data source.

Type: System.Threading.Tasks.ParallelOptions

An object that configures the behavior of this operation.

Type: System.Action(TSource)

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.


The CancellationToken in the parallelOptions argument is canceled.


The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.


The source argument is a null reference (Nothing in Visual Basic).


The parallelOptions argument is a null reference (Nothing in Visual Basic).


The body argument is a null reference (Nothing in Visual Basic).


The SupportsDynamicPartitions property in the source partitioner returns false.


The exception that is thrown when any methods in the source partitioner return a null reference (Nothing in Visual Basic).

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 method expects custom partitioners to support dynamic partitioning. For more information, see Custom Partitioners for PLINQ and TPL and How to: Implement Dynamic Partitions.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1
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