ConcurrentDictionary<TKey, TValue>.GetOrAdd Method (TKey, Func<TKey, TValue>)

Adds a key/value pair to the ConcurrentDictionary<TKey, TValue> by using the specified function, if the key does not already exist.

Namespace:  System.Collections.Concurrent
Assemblies:   System.Collections.Concurrent (in System.Collections.Concurrent.dll)
  mscorlib (in mscorlib.dll)

public TValue GetOrAdd(
	TKey key,
	Func<TKey, TValue> valueFactory


Type: TKey

The key of the element to add.

Type: System.Func<TKey, TValue>

The function used to generate a value for the key

Return Value

Type: TValue
The value for the key. This will be either the existing value for the key if the key is already in the dictionary, or the new value for the key as returned by valueFactory if the key was not in the dictionary.


key or valueFactory is null.


The dictionary already contains the maximum number of elements (MaxValue).

If you call GetOrAdd simultaneously on different threads, addValueFactory may be called multiple times, but its key/value pair might not be added to the dictionary for every call.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Windows Phone 8.1, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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