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

.NET Framework (current version)

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

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

public TValue AddOrUpdate(
	TKey key,
	TValue addValue,
	Func<TKey, TValue, TValue> updateValueFactory


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<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).

Exception Condition

key or updateValueFactory is null.


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

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

using System;
using System.Collections.Concurrent;

class CD_Ctor
    // Demonstrates: 
    //      ConcurrentDictionary<TKey, TValue> ctor(concurrencyLevel, initialCapacity) 
    //      ConcurrentDictionary<TKey, TValue>[TKey] 
    static void 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. 
        int HIGHNUMBER = 64;
        int initialCapacity = 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. 
        int numProcs = Environment.ProcessorCount;
        int concurrencyLevel = numProcs * 2;

        // Construct the dictionary with the desired concurrencyLevel and initialCapacity
        ConcurrentDictionary<int, int> cd = new ConcurrentDictionary<int, int>(concurrencyLevel, initialCapacity);

        // Initialize the dictionary 
        for (int i = 1; i <= HIGHNUMBER; i++) 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 (int i = 1; i <= HIGHNUMBER + 1; i++)
          cd.AddOrUpdate(i, i * i, (k,v) => v / i);

        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)));


Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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