ConcurrentDictionary<TKey,TValue> 类
定义
重要
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表示可同时由多个线程访问的键/值对的线程安全集合。
generic <typename TKey, typename TValue>
public ref class ConcurrentDictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IDictionary<TKey, TValue>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyCollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyDictionary<TKey, TValue>, System::Collections::IDictionarygeneric <typename TKey, typename TValue>
public ref class ConcurrentDictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IDictionary<TKey, TValue>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::IDictionarypublic class ConcurrentDictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>, System.Collections.IDictionary[System.Runtime.InteropServices.ComVisible(false)]
[System.Serializable]
public class ConcurrentDictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.IDictionary[System.Runtime.InteropServices.ComVisible(false)]
[System.Serializable]
public class ConcurrentDictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>, System.Collections.IDictionarypublic class ConcurrentDictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.IDictionarytype ConcurrentDictionary<'Key, 'Value> = class
interface ICollection<KeyValuePair<'Key, 'Value>>
interface seq<KeyValuePair<'Key, 'Value>>
interface IEnumerable
interface IDictionary<'Key, 'Value>
interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
interface IReadOnlyDictionary<'Key, 'Value>
interface ICollection
interface IDictionary[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type ConcurrentDictionary<'Key, 'Value> = class
interface IDictionary<'Key, 'Value>
interface ICollection<KeyValuePair<'Key, 'Value>>
interface seq<KeyValuePair<'Key, 'Value>>
interface IDictionary
interface ICollection
interface IEnumerable[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type ConcurrentDictionary<'Key, 'Value> = class
interface IDictionary<'Key, 'Value>
interface ICollection<KeyValuePair<'Key, 'Value>>
interface seq<KeyValuePair<'Key, 'Value>>
interface IEnumerable
interface IDictionary
interface ICollection
interface IReadOnlyDictionary<'Key, 'Value>
interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>type ConcurrentDictionary<'Key, 'Value> = class
interface IDictionary<'Key, 'Value>
interface ICollection<KeyValuePair<'Key, 'Value>>
interface seq<KeyValuePair<'Key, 'Value>>
interface IDictionary
interface ICollection
interface IEnumerablePublic Class ConcurrentDictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IDictionary, IDictionary(Of TKey, TValue), IEnumerable(Of KeyValuePair(Of TKey, TValue)), IReadOnlyCollection(Of KeyValuePair(Of TKey, TValue)), IReadOnlyDictionary(Of TKey, TValue)Public Class ConcurrentDictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IDictionary, IDictionary(Of TKey, TValue), IEnumerable(Of KeyValuePair(Of TKey, TValue))类型参数
- TKey
字典中键的类型。
- TValue
字典中值的类型。
- 继承
-
ConcurrentDictionary<TKey,TValue>
- 属性
- 实现
-
ICollection<KeyValuePair<TKey,TValue>> IDictionary<TKey,TValue> IEnumerable<KeyValuePair<TKey,TValue>> IEnumerable<T> IReadOnlyCollection<KeyValuePair<TKey,TValue>> IReadOnlyDictionary<TKey,TValue> ICollection IDictionary IEnumerable
示例
以下示例演示如何构造 ConcurrentDictionary<TKey,TValue> 对象。
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 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 initialCapacity
ConcurrentDictionary<int, int> cd = new ConcurrentDictionary<int, int>(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);
}
}
// Demonstrates:
// ConcurrentDictionary<TKey, TValue> ctor(concurrencyLevel, initialCapacity)
// ConcurrentDictionary<TKey, TValue>[TKey]
// 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.
let NUMITEMS = 64
let 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.
let numProcs = Environment.ProcessorCount
let concurrencyLevel = numProcs * 2
// Construct the dictionary with the desired concurrencyLevel and initialCapacity
let cd = ConcurrentDictionary<int, int>(concurrencyLevel, initialCapacity)
// Initialize the dictionary
for i = 0 to NUMITEMS - 1 do
cd[i] <- i * i
printfn $"The square of 23 is {cd[23]} (should be {23 * 23})"
Imports System.Collections.Concurrent
Imports System.Threading.Tasks
Class CD_Ctor
' Demonstrates:
' ConcurrentDictionary<TKey, TValue> ctor(concurrencyLevel, initialCapacity)
' ConcurrentDictionary<TKey, TValue>[TKey]
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 NUMITEMS 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 = 0 To NUMITEMS - 1
cd(i) = i * i
Next
Console.WriteLine("The square of 23 is {0} (should be {1})", cd(23), 23 * 23)
End Sub
End Class
注解
对于非常大的 ConcurrentDictionary<TKey,TValue> 对象，可以将 64 位系统上的最大数组大小增加到 2 GB（GB），方法是在运行时环境中将 <gcAllowVeryLargeObjects> 配置元素设置为 true。
注意
ConcurrentDictionary<TKey,TValue> 实现从 .NET Framework 4.6 开始的 IReadOnlyCollection<T> 和 IReadOnlyDictionary<TKey,TValue> 接口;在早期版本的 .NET Framework 中，ConcurrentDictionary<TKey,TValue> 类未实现这些接口。
与 System.Collections.Generic.Dictionary<TKey,TValue> 类一样，ConcurrentDictionary<TKey,TValue> 实现 IDictionary<TKey,TValue> 接口。 此外，ConcurrentDictionary<TKey,TValue> 提供了几种方法用于在字典中添加或更新键/值对，如下表所述。
| 为此 | 使用此方法 | 使用情况说明 |
|---|---|---|
| 将新键添加到字典（如果字典中尚不存在） | TryAdd | 如果字典中当前不存在该键，此方法将添加指定的键/值对。 该方法根据是否添加了新对返回 true 或 false。 |
| 更新字典中现有键的值（如果该键具有特定值） | TryUpdate | 此方法检查密钥是否具有指定的值，如果具有指定值，则使用新值更新密钥。 它类似于 CompareExchange 方法，只不过它用于字典元素。 |
| 无条件地将键/值对存储在字典中，并覆盖已存在的键的值 | 索引器的 setter：dictionary[key] = newValue |
|
| 将键/值对添加到字典，或者如果键已存在，请根据键的现有值更新键的值 | AddOrUpdate(TKey, Func<TKey,TValue>, Func<TKey,TValue,TValue>) -或- AddOrUpdate(TKey, TValue, Func<TKey,TValue,TValue>) |
AddOrUpdate(TKey, Func<TKey,TValue>, Func<TKey,TValue,TValue>) 接受密钥和两个委托。 如果字典中不存在键，它将使用第一个委托;它接受密钥并返回应为密钥添加的值。 如果密钥存在，它将使用第二个委托;它接受键及其当前值，并返回应为键设置的新值。 AddOrUpdate(TKey, TValue, Func<TKey,TValue,TValue>) 接受密钥、要添加的值和更新委托。 这与上一个重载相同，不同之处在于它不使用委托添加密钥。 |
| 获取字典中某个键的值，将值添加到字典，并在键不存在时返回它 | GetOrAdd(TKey, TValue) -或- GetOrAdd(TKey, Func<TKey,TValue>) |
这些重载为字典中的键/值对提供延迟初始化，仅当键/值对不存在时才添加值。 GetOrAdd(TKey, TValue) 如果键不存在，则采用要添加的值。 GetOrAdd(TKey, Func<TKey,TValue>) 采用一个委托，如果键不存在，将生成值。 |
所有这些操作都是原子操作，对于 ConcurrentDictionary<TKey,TValue> 类上的所有其他操作，都是线程安全的。 唯一的例外是接受委托的方法，即 AddOrUpdate 和 GetOrAdd。 对于对字典的修改和写入操作，ConcurrentDictionary<TKey,TValue> 使用精细锁定来确保线程安全。 （字典上的读取操作以无锁方式执行。但是，这些方法的委托在锁外部调用，以避免在锁下执行未知代码时可能出现的问题。 因此，这些委托执行的代码不受操作的原子性的约束。
构造函数
属性
| Comparer |
获取用于确定字典键相等性的 IEqualityComparer<T>。 |
| Count |
获取 ConcurrentDictionary<TKey,TValue>中包含的键/值对数。 |
| IsEmpty |
获取一个值，该值指示 ConcurrentDictionary<TKey,TValue> 是否为空。 |
| Item[TKey] |
获取或设置与指定键关联的值。 |
| Keys |
获取包含 Dictionary<TKey,TValue>中的键的集合。 |
| Values |
获取一个集合，该集合包含 Dictionary<TKey,TValue>中的值。 |
方法
显式接口实现
扩展方法
适用于
线程安全性
ConcurrentDictionary<TKey,TValue> 的所有公共和受保护成员都是线程安全的，可以从多个线程并发使用。 但是，ConcurrentDictionary<TKey,TValue> 实现的其中一个接口（包括扩展方法）访问的成员不能保证线程安全，并且可能需要由调用方同步。
