ConcurrentDictionary<TKey,TValue>.AddOrUpdate Method

Definition

Namespace:

System.Collections.Concurrent

Assemblies:

netstandard.dll, System.Collections.Concurrent.dll

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> if the key already exists.

Overloads

AddOrUpdate(TKey, Func<TKey,TValue>, Func<TKey,TValue,TValue>)	Uses the specified functions to add a key/value pair to the ConcurrentDictionary<TKey,TValue> if the key does not already exist, or to update a key/value pair in the ConcurrentDictionary<TKey,TValue> if the key already exists.
AddOrUpdate(TKey, TValue, Func<TKey,TValue,TValue>)	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.
AddOrUpdate<TArg>(TKey, Func<TKey,TArg,TValue>, Func<TKey,TValue,TArg,TValue>, TArg)	Uses the specified functions and argument to add a key/value pair to the ConcurrentDictionary<TKey,TValue> if the key does not already exist, or to update a key/value pair in the ConcurrentDictionary<TKey,TValue> if the key already exists.

Examples

The following example shows how to call the AddOrUpdate method:

C#

class CD_GetOrAddOrUpdate
{
    // Demonstrates:
    //      ConcurrentDictionary<TKey, TValue>.AddOrUpdate()
    //      ConcurrentDictionary<TKey, TValue>.GetOrAdd()
    //      ConcurrentDictionary<TKey, TValue>[]
    static void Main()
    {
        // Construct a ConcurrentDictionary
        ConcurrentDictionary<int, int> cd = new ConcurrentDictionary<int, int>();

        // Bombard the ConcurrentDictionary with 10000 competing AddOrUpdates
        Parallel.For(0, 10000, i =>
        {
            // Initial call will set cd[1] = 1.
            // Ensuing calls will set cd[1] = cd[1] + 1
            cd.AddOrUpdate(1, 1, (key, oldValue) => oldValue + 1);
        });

        Console.WriteLine("After 10000 AddOrUpdates, cd[1] = {0}, should be 10000", cd[1]);

        // Should return 100, as key 2 is not yet in the dictionary
        int value = cd.GetOrAdd(2, (key) => 100);
        Console.WriteLine("After initial GetOrAdd, cd[2] = {0} (should be 100)", value);

        // Should return 100, as key 2 is already set to that value
        value = cd.GetOrAdd(2, 10000);
        Console.WriteLine("After second GetOrAdd, cd[2] = {0} (should be 100)", value);
    }
}

AddOrUpdate(TKey, Func<TKey,TValue>, Func<TKey,TValue,TValue>)

Source:

ConcurrentDictionary.cs

Uses the specified functions to add a key/value pair to the ConcurrentDictionary<TKey,TValue> if the key does not already exist, or to update a key/value pair in the ConcurrentDictionary<TKey,TValue> if the key already exists.

C#

public TValue AddOrUpdate(TKey key, Func<TKey,TValue> addValueFactory, Func<TKey,TValue,TValue> updateValueFactory);

Parameters

key

TKey

The key to be added or whose value should be updated.

addValueFactory

Func<TKey,TValue>

The function used to generate a value for an absent key.

updateValueFactory

Func<TKey,TValue,TValue>

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

Returns

TValue

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

Exceptions

ArgumentNullException

key, addValueFactory, or updateValueFactory is null.

OverflowException

The dictionary contains too many elements.

Remarks

If you call AddOrUpdate 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.

For modifications and write operations to the dictionary, ConcurrentDictionary<TKey,TValue> uses fine-grained locking to ensure thread safety (read operations on the dictionary are performed in a lock-free manner). The addValueFactory and updateValueFactory delegates may be executed multiple times to verify the value was added or updated as expected. However, they are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, AddOrUpdate is not atomic with regards to all other operations on the ConcurrentDictionary<TKey,TValue> class.

See also

• Thread-Safe Collections
• How to: Add and Remove Items from a ConcurrentDictionary

AddOrUpdate(TKey, TValue, Func<TKey,TValue,TValue>)

Source:

ConcurrentDictionary.cs

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.

C#

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

Parameters

key

TKey

The key to be added or whose value should be updated.

addValue

TValue

The value to be added for an absent key.

updateValueFactory

Func<TKey,TValue,TValue>

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

Returns

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).

Exceptions

ArgumentNullException

key or updateValueFactory is null.

OverflowException

The dictionary contains too many elements.

Examples

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.

C#

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)));
    }
}

For modifications and write operations to the dictionary, ConcurrentDictionary<TKey,TValue> uses fine-grained locking to ensure thread safety. (Read operations on the dictionary are performed in a lock-free manner.) The addValueFactory and updateValueFactory delegates may be executed multiple times to verify the value was added or updated as expected. However, they are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, AddOrUpdate is not atomic with regards to all other operations on the ConcurrentDictionary<TKey,TValue> class.

See also

• Thread-Safe Collections
• How to: Add and Remove Items from a ConcurrentDictionary

AddOrUpdate<TArg>(TKey, Func<TKey,TArg,TValue>, Func<TKey,TValue,TArg,TValue>, TArg)

Source:

ConcurrentDictionary.cs

Uses the specified functions and argument to add a key/value pair to the ConcurrentDictionary<TKey,TValue> if the key does not already exist, or to update a key/value pair in the ConcurrentDictionary<TKey,TValue> if the key already exists.

C#

public TValue AddOrUpdate<TArg>(TKey key, Func<TKey,TArg,TValue> addValueFactory, Func<TKey,TValue,TArg,TValue> updateValueFactory, TArg factoryArgument);

Type Parameters

TArg

The type of an argument to pass into addValueFactory and updateValueFactory.

Parameters

key

TKey

The key to be added or whose value should be updated.

addValueFactory

Func<TKey,TArg,TValue>

The function used to generate a value for an absent key.

updateValueFactory

Func<TKey,TValue,TArg,TValue>

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

factoryArgument

TArg

An argument to pass into addValueFactory and updateValueFactory.

Returns

TValue

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

Exceptions

ArgumentNullException

key, addValueFactory, or updateValueFactory is a null reference (Nothing in Visual Basic).

OverflowException

The dictionary contains too many elements.

Remarks

If you call AddOrUpdate 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.

For modifications and write operations to the dictionary, ConcurrentDictionary<TKey,TValue> uses fine-grained locking to ensure thread safety. (Read operations on the dictionary are performed in a lock-free manner.) The addValueFactory and updateValueFactory delegates may be executed multiple times to verify the value was added or updated as expected. However, they are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, AddOrUpdate is not atomic with regards to all other operations on the ConcurrentDictionary<TKey,TValue> class.