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ParallelEnumerable.FirstOrDefault<TSource> Method (ParallelQuery<TSource>, Func<TSource, Boolean>)

Returns the first element of the parallel sequence that satisfies a condition or a default value if no such element is found.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

public static TSource FirstOrDefault<TSource>(
	this ParallelQuery<TSource> source,
	Func<TSource, bool> predicate

Type Parameters


The type of the elements of source.


Type: System.Linq.ParallelQuery<TSource>
The sequence to return an element from.
Type: System.Func<TSource, Boolean>
A function to test each element for a condition.

Return Value

Type: TSource
default(TSource) if source is empty or if no element passes the test specified by predicate; otherwise, the first element in source that passes the test specified by predicate.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type ParallelQuery<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


The query was canceled with the token passed in through WithCancellation.


source or predicate is a null reference (Nothing in Visual Basic).


One or more exceptions occurred during the evaluation of the query.

If the query is not ordered, then the first element is non-deterministic. For more information, see Order Preservation in PLINQ.

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.