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ConcurrentDictionary(Of TKey, TValue).AddOrUpdate Method (TKey, TValue, Func(Of TKey, TValue, TValue))

Adds a key/value pair to the ConcurrentDictionary(Of TKey, TValue) if the key does not already exist, or updates a key/value pair in the ConcurrentDictionary(Of TKey, TValue) by using the specified function if the key already exists.

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

Public Function AddOrUpdate ( _
	key As TKey, _
	addValue As TValue, _
	updateValueFactory As Func(Of TKey, TValue, TValue) _
) As TValue


Type: TKey

The key to be added or whose value should be updated

Type: TValue

The value to be added for an absent key

Type: System.Func(Of TKey, TValue, TValue)

The function used to generate a new value for an existing key based on the key's existing value

Return Value

Type: TValue
The new value for the key. This will be either be addValue (if the key was absent) or the result of updateValueFactory (if the key was present).


key or updateValueFactory is Nothing.


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

The following code example shows how to initialize an ConcurrentDictionary(Of TKey, TValue) and how to use the AddOrUpdate method to add an additional item to the collection, and update the existing items.

Imports System.Collections.Concurrent

Class CD_Ctor
    ' Demonstrates:  
    '      ConcurrentDictionary<TKey, TValue> ctor(concurrencyLevel, initialCapacity)  
    '      ConcurrentDictionary<TKey, TValue>[TKey]  
    Public Shared Sub Main()
        ' We know how many items we want to insert into the ConcurrentDictionary.  
        ' So set the initial capacity to some prime number above that, to ensure that  
        ' the ConcurrentDictionary does not need to be resized while initializing it.  
        Dim HIGHNUMBER As Integer = 64
        Dim initialCapacity As Integer = 101

        ' The higher the concurrencyLevel, the higher the theoretical number of operations  
        ' that could be performed concurrently on the ConcurrentDictionary.  However, global  
        ' operations like resizing the dictionary take longer as the concurrencyLevel rises.   
        ' For the purposes of this example, we'll compromise at numCores * 2.  
        Dim numProcs As Integer = Environment.ProcessorCount
        Dim concurrencyLevel As Integer = numProcs * 2

        ' Construct the dictionary with the desired concurrencyLevel and initialCapacity 
        Dim cd As New ConcurrentDictionary(Of Integer, Integer)(concurrencyLevel, initialCapacity)

        ' Initialize the dictionary  
        For i As Integer = 1 To HIGHNUMBER
            cd(i) = i * i

        Console.WriteLine("The square of 23 is {0} (should be {1})", cd(23), 23 * 23)

        ' Now iterate through, adding one to the end of the list. Existing items should be updated to be divided by their  
        ' key  and a new item will be added that is the square of its key. 
        For i As Integer = 1 To HIGHNUMBER + 1

            cd.AddOrUpdate(i, i * i, Function(k, v)
                                         Return v / i
                                     End Function)

        Console.WriteLine("The square root of 529 is {0} (should be {1})", cd(23), 529 / 23)
        Console.WriteLine("The square of 65 is {0} (should be {1})", cd(HIGHNUMBER + 1), ((HIGHNUMBER + 1) * (HIGHNUMBER + 1)))

    End Sub 
End Class

.NET Framework

Supported in: 4.5.2, 4.5.1, 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

.NET for Windows Phone apps

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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