CountdownEvent 类
定义
重要
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表示在计数变为零时处于有信号状态的同步基元。
public ref class CountdownEvent : IDisposablepublic class CountdownEvent : IDisposable[System.Runtime.InteropServices.ComVisible(false)]
public class CountdownEvent : IDisposabletype CountdownEvent = class
interface IDisposable[<System.Runtime.InteropServices.ComVisible(false)>]
type CountdownEvent = class
interface IDisposablePublic Class CountdownEvent
Implements IDisposable- 继承
-
CountdownEvent
- 属性
- 实现
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
| CountdownEvent(Int32) |
使用指定计数初始化 CountdownEvent 类的新实例。 |
属性
| CurrentCount |
获取设置事件时所必需的剩余信号数。 |
| InitialCount |
获取设置事件时最初必需的信号数。 |
| IsSet |
表示 CountdownEvent 对象的当前计数是否已归零。 |
| WaitHandle |
获取用于等待要设置的事件的 WaitHandle。 |
方法
适用于
线程安全性
所有公共成员和受保护的成员CountdownEvent都是线程安全的，并且可能同时从多个线程使用，但例外是，只有在Dispose()已完成所有其他操作CountdownEventReset()时才使用，并且仅在没有其他线程访问事件时才使用。