CountdownEvent 类

定义

命名空间:

System.Threading

程序集:

netstandard.dll, System.Threading.dll

Source:

CountdownEvent.cs

表示在计数达到零时发出信号的同步基元。

public ref class CountdownEvent : IDisposable

public class CountdownEvent : IDisposable

type CountdownEvent = class
    interface IDisposable

Public Class CountdownEvent
Implements IDisposable

继承

Object

CountdownEvent

实现

IDisposable

示例

以下示例演示如何使用CountdownEvent：

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

class Example
{
    static async Task Main()
    {
        // Initialize a queue and a CountdownEvent
        ConcurrentQueue<int> queue = new ConcurrentQueue<int>(Enumerable.Range(0, 10000));
        CountdownEvent cde = new CountdownEvent(10000); // initial count = 10000

        // This is the logic for all queue consumers
        Action consumer = () =>
        {
            int local;
            // decrement CDE count once for each element consumed from queue
            while (queue.TryDequeue(out local)) cde.Signal();
        };

        // Now empty the queue with a couple of asynchronous tasks
        Task t1 = Task.Factory.StartNew(consumer);
        Task t2 = Task.Factory.StartNew(consumer);

        // And wait for queue to empty by waiting on cde
        cde.Wait(); // will return when cde count reaches 0

        Console.WriteLine("Done emptying queue.  InitialCount={0}, CurrentCount={1}, IsSet={2}",
            cde.InitialCount, cde.CurrentCount, cde.IsSet);

        // Proper form is to wait for the tasks to complete, even if you know that their work
        // is done already.
        await Task.WhenAll(t1, t2);

        // Resetting will cause the CountdownEvent to un-set, and resets InitialCount/CurrentCount
        // to the specified value
        cde.Reset(10);

        // AddCount will affect the CurrentCount, but not the InitialCount
        cde.AddCount(2);

        Console.WriteLine("After Reset(10), AddCount(2): InitialCount={0}, CurrentCount={1}, IsSet={2}",
            cde.InitialCount, cde.CurrentCount, cde.IsSet);

        // Now try waiting with cancellation
        CancellationTokenSource cts = new CancellationTokenSource();
        cts.Cancel(); // cancels the CancellationTokenSource
        try
        {
            cde.Wait(cts.Token);
        }
        catch (OperationCanceledException)
        {
            Console.WriteLine("cde.Wait(preCanceledToken) threw OCE, as expected");
        }
        finally
        {
           cts.Dispose();
        }
        // It's good to release a CountdownEvent when you're done with it.
        cde.Dispose();
    }
}
// The example displays the following output:
//    Done emptying queue.  InitialCount=10000, CurrentCount=0, IsSet=True
//    After Reset(10), AddCount(2): InitialCount=10, CurrentCount=12, IsSet=False
//    cde.Wait(preCanceledToken) threw OCE, as expected

Imports System.Collections.Concurrent
Imports System.Linq
Imports System.Threading
Imports System.Threading.Tasks

Module Example
    Sub Main()
        ' Initialize a queue and a CountdownEvent
        Dim queue As New ConcurrentQueue(Of Integer)(Enumerable.Range(0, 10000))
        Dim cde As New CountdownEvent(10000)
        ' initial count = 10000
        ' This is the logic for all queue consumers
        Dim consumer As Action =
            Sub()
                Dim local As Integer
                ' decrement CDE count once for each element consumed from queue
                While queue.TryDequeue(local)
                    cde.Signal()
                End While
            End Sub

        ' Now empty the queue with a couple of asynchronous tasks
        Dim t1 As Task = Task.Factory.StartNew(consumer)
        Dim t2 As Task = Task.Factory.StartNew(consumer)

        ' And wait for queue to empty by waiting on cde
        cde.Wait()
        ' will return when cde count reaches 0
        Console.WriteLine("Done emptying queue. InitialCount={0}, CurrentCount={1}, IsSet={2}", cde.InitialCount, cde.CurrentCount, cde.IsSet)

        ' Proper form is to wait for the tasks to complete, even if you know that their work
        ' is done already.
        Task.WaitAll(t1, t2)

        ' Resetting will cause the CountdownEvent to un-set, and resets InitialCount/CurrentCount
        ' to the specified value
        cde.Reset(10)

        ' AddCount will affect the CurrentCount, but not the InitialCount
        cde.AddCount(2)

        Console.WriteLine("After Reset(10), AddCount(2): InitialCount={0}, CurrentCount={1}, IsSet={2}", cde.InitialCount, cde.CurrentCount, cde.IsSet)

        ' Now try waiting with cancellation
        Dim cts As New CancellationTokenSource()
        cts.Cancel()
        ' cancels the CancellationTokenSource
        Try
            cde.Wait(cts.Token)
        Catch generatedExceptionName As OperationCanceledException
            Console.WriteLine("cde.Wait(preCanceledToken) threw OCE, as expected")
        Finally
           cts.Dispose()
        End Try

        ' It's good to release a CountdownEvent when you're done with it.
        cde.Dispose()
    End Sub
End Module
' The example displays the following output:
'    Done emptying queue.  InitialCount=10000, CurrentCount=0, IsSet=True
'    After Reset(10), AddCount(2): InitialCount=10, CurrentCount=12, IsSet=False
'    cde.Wait(preCanceledToken) threw OCE, as expected

构造函数

名称	说明
CountdownEvent(Int32)	使用指定的计数初始化类的新实例 CountdownEvent 。

属性

名称	说明
CurrentCount	获取设置事件所需的剩余信号数。
InitialCount	获取最初设置事件所需的信号数。
IsSet	指示对象的 CountdownEvent 当前计数是否已达到零。
WaitHandle	获取一个用于等待设置事件的项 WaitHandle 。

方法

名称	说明
AddCount()	将 CountdownEvent当前计数递增一个。
AddCount(Int32)	CountdownEvent按指定值递增'当前计数。
Dispose()	释放类的 CountdownEvent 当前实例使用的所有资源。
Dispose(Boolean)	释放由该资源使用 CountdownEvent的非托管资源，并选择性地释放托管资源。
Equals(Object)	确定指定的对象是否等于当前对象。 (继承自 Object)
GetHashCode()	用作默认哈希函数。 (继承自 Object)
GetType()	获取当前实例的 Type。 (继承自 Object)
MemberwiseClone()	创建当前 Object的浅表副本。 (继承自 Object)
Reset()	重置为 /a0> 的值 。
Reset(Int32)	将 InitialCount 属性重置为指定的值。
Signal()	向值递减CountdownEvent的信号CurrentCount注册信号。
Signal(Int32)	将多个信号注册到 CountdownEvent指定的量递减的值 CurrentCount 。
ToString()	返回一个表示当前对象的字符串。 (继承自 Object)
TryAddCount()	尝试递增 CurrentCount 一个。
TryAddCount(Int32)	尝试按指定值递增 CurrentCount 。
Wait()	阻止当前线程，直到设置。CountdownEvent
Wait(CancellationToken)	在观察 CountdownEvent 时阻止当前线程，直到CancellationToken设置 。
Wait(Int32, CancellationToken)	在设置当前线程之前 CountdownEvent ，使用 32 位有符号整数测量超时，同时观察超时 CancellationToken。
Wait(Int32)	在设置当前线程之前 CountdownEvent ，使用 32 位有符号整数测量超时。
Wait(TimeSpan, CancellationToken)	阻止当前线程， CountdownEvent 直到设置，使用 a TimeSpan 测量超时，同时观察一个 CancellationToken。
Wait(TimeSpan)	阻止当前线程， CountdownEvent 直到设置该线程，并使用 a TimeSpan 来度量超时。

线程安全性

所有公共和受保护的成员CountdownEvent都是线程安全的，并且可以同时从多个线程使用，但例外是，只有在Dispose()已完成CountdownEvent所有其他操作Reset()时才使用，并且只有在没有其他线程访问该事件时才应使用。

另请参阅

• CountdownEvent