DataflowBlock.Choose<T1, T2, T3> Method (ISourceBlock<T1>, Action<T1>, ISourceBlock<T2>, Action<T2>, ISourceBlock<T3>, Action<T3>, DataflowBlockOptions)

.NET Framework (current version)

Monitors three dataflow sources, invoking the provided handler for whichever source makes data available first.

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

public static Task<int> Choose<T1, T2, T3>(
	ISourceBlock<T1> source1,
	Action<T1> action1,
	ISourceBlock<T2> source2,
	Action<T2> action2,
	ISourceBlock<T3> source3,
	Action<T3> action3,
	DataflowBlockOptions dataflowBlockOptions

Type Parameters


Specifies type of data contained in the first source.


Specifies type of data contained in the second source.


Specifies type of data contained in the third source.


Type: System.Threading.Tasks.Dataflow.ISourceBlock<T1>

The first source.

Type: System.Action<T1>

The handler to execute on data from the first source.

Type: System.Threading.Tasks.Dataflow.ISourceBlock<T2>

The second source.

Type: System.Action<T2>

The handler to execute on data from the second source.

Type: System.Threading.Tasks.Dataflow.ISourceBlock<T3>

The third source.

Type: System.Action<T3>

The handler to execute on data from the third source.

Type: System.Threading.Tasks.Dataflow.DataflowBlockOptions

The options with which to configure this choice.

Return Value

Type: System.Threading.Tasks.Task<Int32>
A Task<TResult> that represents the asynchronous choice. If all sources are completed prior to the choice completing, or if the CancellationToken provided as part of dataflowBlockOptions is canceled prior to the choice completing, the resulting task will be canceled. When one of the sources has data available and successfully propagates it to the choice, the resulting task will complete when the handler completes; if the handler throws an exception, the task will end in the Faulted state and will contain the unhandled exception. Otherwise, the task will end with its Result set to the 0-based index of the source.
This method will only consume an element from one of the data sources, never more than one. If cancellation is requested after an element has been received, the cancellation request will be ignored, and the relevant handler will be allowed to execute.


The source1 is null.


The action1 is null.


The source2 is null.


The action2 is null.


The source3 is null.


The action3 is null.


The dataflowBlockOptions is null.

.NET Framework

Supported in: 4.5

Portable Class Library

Supported in: Portable Class Library