ConcurrentDictionary<TKey,TValue> Class

Represents a thread-safe collection of key/value pairs that can be accessed by multiple threads concurrently.

Namespace:

Assembly: mscorlib (in mscorlib.dll)

System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>

[SerializableAttribute][ComVisibleAttribute(false)][HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 	ExternalThreading = true)]	public class ConcurrentDictionary
     
       : IDictionary
      
       , 	ICollection
       
        
         >, IEnumerable
         
          
           > ,IEnumerable, IDictionary, ICollection, IReadOnlyDictionary
           
            ,  IReadOnlyCollection
            
             
              >

Type Parameters

TKey

The type of the keys in the dictionary.

TValue

The type of the values in the dictionary.

	Name	Description
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that is empty, has the default concurrency level, has the default initial capacity, and uses the default comparer for the key type.
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that contains elements copied from the specified , has the default concurrency level, has the default initial capacity, and uses the default comparer for the key type.
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that contains elements copied from the specified has the default concurrency level, has the default initial capacity, and uses the specified .
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that is empty, has the default concurrency level and capacity, and uses the specified .
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that contains elements copied from the specified , and uses the specified .
		Initializes a new instance of the ConcurrentDictionary<TKey,TValue> class that is empty, has the specified concurrency level and capacity, and uses the default comparer for the key type.
		Initializes a new instance of the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue> class that is empty, has the specified concurrency level, has the specified initial capacity, and uses the specified .

	Name	Description
		Gets the number of key/value pairs contained in the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>.
		Gets a value that indicates whether the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue> is empty.
		Gets or sets the value associated with the specified key.
		Gets a collection containing the keys in the .
		Gets a collection that contains the values in the .

	Name	Description
		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.
		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.
		Removes all keys and values from the ConcurrentDictionary<TKey,TValue>.
		Determines whether the ConcurrentDictionary<TKey,TValue> contains the specified key.
		Determines whether the specified object is equal to the current object.(Inherited from .)
		Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from .)
		Returns an enumerator that iterates through the ConcurrentDictionary<TKey,TValue>.
		Serves as the default hash function. (Inherited from .)
		Adds a key/value pair to the ConcurrentDictionary<TKey,TValue> if the key does not already exist.
		Adds a key/value pair to the ConcurrentDictionary<TKey,TValue> by using the specified function, if the key does not already exist.
		Gets the of the current instance.(Inherited from .)
		Creates a shallow copy of the current .(Inherited from .)
		Copies the key and value pairs stored in the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue> to a new array.
		Returns a string that represents the current object.(Inherited from .)
		Attempts to add the specified key and value to the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>.
		Attempts to get the value associated with the specified key from the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>.
		Attempts to remove and return the value that has the specified key from the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>.
		Compares the existing value for the specified key with a specified value, and if they are equal, updates the key with a third value.

	Name	Description
		Adds an item to the collection.
		Gets whether the contains an element with the specified key.
		Copies the elements of the to an array, starting at the specified array index.
		Removes the specified key/value pair from the collection.
		Adds the specified key and value to the .
		Removes the element with the specified key from the .
		Copies the elements of the to an array, starting at the specified array index.
		Adds the specified key and value to the dictionary.
		Gets whether the contains an element with the specified key.
		Provides a for the .
		Removes the element with the specified key from the .
		Returns an enumerator that iterates through the System.Collections.Concurrent.ConcurrentDictionary<TKey,TValue>.
		Gets a value indicating whether the is read-only.
		Gets a collection containing the keys in the .
		Gets a collection that contains the values in the .
		Gets a value indicating whether access to the is synchronized with the SyncRoot.
		Gets an object that can be used to synchronize access to the . This property is not supported.
		Gets a value indicating whether the has a fixed size.
		Gets a value indicating whether the is read-only.
		Gets or sets the value associated with the specified key.
		Gets an that contains the keys of the .
		Gets an that contains the values in the .

	Name	Description
		Overloaded. Applies an accumulator function over a sequence.(Defined by .)
		Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value.(Defined by .)
		Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value.(Defined by .)
		Determines whether all elements of a sequence satisfy a condition.(Defined by .)
		Overloaded. Determines whether a sequence contains any elements.(Defined by .)
		Overloaded. Determines whether any element of a sequence satisfies a condition.(Defined by .)
		Returns the input typed as .(Defined by .)
		Overloaded. Enables parallelization of a query.(Defined by .)
		Overloaded. Enables parallelization of a query.(Defined by .)
		Overloaded. Converts an to an .(Defined by .)
		Overloaded. Converts a generic to a generic .(Defined by .)
		Overloaded. Computes the average of a sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the average of a sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Casts the elements of an to the specified type.(Defined by .)
		Concatenates two sequences.(Defined by .)
		Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer.(Defined by .)
		Overloaded. Determines whether a sequence contains a specified element by using a specified .(Defined by .)
		Overloaded. Returns the number of elements in a sequence.(Defined by .)
		Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition.(Defined by .)
		Overloaded. Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty.(Defined by .)
		Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty.(Defined by .)
		Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values.(Defined by .)
		Overloaded. Returns distinct elements from a sequence by using a specified to compare values.(Defined by .)
		Returns the element at a specified index in a sequence.(Defined by .)
		Returns the element at a specified index in a sequence or a default value if the index is out of range.(Defined by .)
		Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values.(Defined by .)
		Overloaded. Produces the set difference of two sequences by using the specified to compare values.(Defined by .)
		Overloaded. Returns the first element of a sequence.(Defined by .)
		Overloaded. Returns the first element in a sequence that satisfies a specified condition.(Defined by .)
		Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements.(Defined by .)
		Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The keys are compared by using a specified comparer.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The elements of each group are projected by using a specified function.(Defined by .)
		Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.(Defined by .)
		Overloaded. Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys.(Defined by .)
		Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified is used to compare keys.(Defined by .)
		Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values.(Defined by .)
		Overloaded. Produces the set intersection of two sequences by using the specified to compare values.(Defined by .)
		Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys.(Defined by .)
		Overloaded. Correlates the elements of two sequences based on matching keys. A specified is used to compare keys.(Defined by .)
		Overloaded. Returns the last element of a sequence.(Defined by .)
		Overloaded. Returns the last element of a sequence that satisfies a specified condition.(Defined by .)
		Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements.(Defined by .)
		Overloaded. Returns the last element of a sequence that satisfies a condition or a default value if no such element is found.(Defined by .)
		Overloaded. Returns an that represents the total number of elements in a sequence.(Defined by .)
		Overloaded. Returns an that represents how many elements in a sequence satisfy a condition.(Defined by .)
		Overloaded. Returns the maximum value in a generic sequence.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the maximum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value.(Defined by .)
		Overloaded. Returns the minimum value in a generic sequence.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a sequence and returns the minimum value.(Defined by .)
		Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value.(Defined by .)
		Filters the elements of an based on a specified type.(Defined by .)
		Overloaded. Sorts the elements of a sequence in ascending order according to a key.(Defined by .)
		Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer.(Defined by .)
		Overloaded. Sorts the elements of a sequence in descending order according to a key.(Defined by .)
		Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer.(Defined by .)
		Inverts the order of the elements in a sequence.(Defined by .)
		Overloaded. Projects each element of a sequence into a new form.(Defined by .)
		Overloaded. Projects each element of a sequence into a new form by incorporating the element's index.(Defined by .)
		Overloaded. Projects each element of a sequence to an and flattens the resulting sequences into one sequence.(Defined by .)
		Overloaded. Projects each element of a sequence to an , and flattens the resulting sequences into one sequence. The index of each source element is used in the projected form of that element.(Defined by .)
		Overloaded. Projects each element of a sequence to an , flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein.(Defined by .)
		Overloaded. Projects each element of a sequence to an , flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element.(Defined by .)
		Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type.(Defined by .)
		Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified .(Defined by .)
		Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.(Defined by .)
		Overloaded. Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.(Defined by .)
		Overloaded. Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence.(Defined by .)
		Overloaded. Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition.(Defined by .)
		Bypasses a specified number of elements in a sequence and then returns the remaining elements.(Defined by .)
		Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements.(Defined by .)
		Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function.(Defined by .)
		Overloaded. Computes the sum of the sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of nullable values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Overloaded. Computes the sum of the sequence of values that are obtained by invoking a transform function on each element of the input sequence.(Defined by .)
		Returns a specified number of contiguous elements from the start of a sequence.(Defined by .)
		Overloaded. Returns elements from a sequence as long as a specified condition is true.(Defined by .)
		Overloaded. Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function.(Defined by .)
		Creates an array from a .(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function.(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function and key comparer.(Defined by .)
		Overloaded. Creates a from an according to specified key selector and element selector functions.(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function, a comparer, and an element selector function.(Defined by .)
		Creates a from an .(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function.(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function and key comparer.(Defined by .)
		Overloaded. Creates a from an according to specified key selector and element selector functions.(Defined by .)
		Overloaded. Creates a from an according to a specified key selector function, a comparer and an element selector function.(Defined by .)
		Overloaded. Produces the set union of two sequences by using the default equality comparer.(Defined by .)
		Overloaded. Produces the set union of two sequences by using a specified .(Defined by .)
		Overloaded. Filters a sequence of values based on a predicate.(Defined by .)
		Overloaded. Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function.(Defined by .)
		Applies a specified function to the corresponding elements of two sequences, producing a sequence of the results.(Defined by .)

For very large ConcurrentDictionary<TKey,TValue> objects, you can increase the maximum array size to 2 gigabytes (GB) on a 64-bit system by setting the configuration element to true in the run-time environment.

System_CAPS_note Note

ConcurrentDictionary<TKey,TValue> implements the and interfaces starting with the .NET Framework 4.6; in previous versions of the .NET Framework, the ConcurrentDictionary<TKey,TValue> class did not implement these interfaces.

Like the class, ConcurrentDictionary<TKey,TValue> implements the interface. In addition, ConcurrentDictionary<TKey,TValue> provides several methods for adding or updating key/value pairs in the dictionary, as described in the following table.

To do this

	Use this method	Usage notes
Add a new key to the dictionary, if it doesn’t already exist in the dictionary		This method adds the specified key/value pair, if the key doesn’t currently exist in the dictionary. The method returns true or false depending on whether the new pair was added.
Update the value for an existing key in the dictionary, if that key has a specific value		This method checks whether the key has a specified value, and if it does, updates the key with a new value. It's similar to the method, except that it's used for dictionary elements.
Store a key/value pair in the dictionary unconditionally, and overwrite the value of a key that already exists	The indexer’s setter: dictionary[key] = newValue
Add a key/value pair to the dictionary, or if the key already exists, update the value for the key based on the key’s existing value	—or—	accepts the key and two delegates. It uses the first delegate if the key doesn’t exist in the dictionary; it accepts the key and returns the value that should be added for the key. It uses the second delegate if the key does exist; it accepts the key and its current value, and it returns the new value that should be set for the key. accepts the key, a value to add, and the update delegate. This is the same as the previous overload, except that it doesn't use a delegate to add a key.
Get the value for a key in the dictionary, adding the value to the dictionary and returning it if the key doesn’t exist	—or—	These overloads provide lazy initialization for a key/value pair in the dictionary, adding the value only if it’s not there. takes the value to be added if the key doesn’t exist. takes a delegate that will generate the value if the key doesn’t exist.

All these operations are atomic and are thread-safe with regards to all other operations on the ConcurrentDictionary<TKey,TValue> class. The only exceptions are the methods that accept a delegate, that is, and . 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.) However, delegates for these methods are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, the code executed by these delegates is not subject to the atomicity of the operation.

The following example shows how to construct a ConcurrentDictionary<TKey,TValue> object.

class CD_Ctor{        // Demonstrates:        //      ConcurrentDictionary
     
       ctor(concurrencyLevel, initialCapacity)//      ConcurrentDictionary
      
       [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 NUMITEMS = 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 initialCapacityConcurrentDictionary
       
         cd = new ConcurrentDictionary
        
         (concurrencyLevel, initialCapacity);             // Initialize the dictionary            for (int i = 0; i < NUMITEMS; i++) cd[i] = i * i;            Console.WriteLine("The square of 23 is {0} (should be {1})",             cd[23], 23 * 23);        }}

备注：转自

转载于:https://blog.51cto.com/jiaojusuimu/1880661

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