- Reference
Definition
- Namespace:
- System.Threading
- Assembly:
- System.Threading.dll
- Assembly:
- mscorlib.dll
- Assembly:
- netstandard.dll
- Source:
- CountdownEvent.cs
- Source:
- CountdownEvent.cs
- Source:
- CountdownEvent.cs
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Represents a synchronization primitive that is signaled when its count reaches zero.
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 CountdownEventImplements IDisposable- Inheritance
Object
CountdownEvent
- Attributes
ComVisibleAttribute
- Implements
IDisposable
Examples
The following example shows how to use a 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 expectedImports System.Collections.ConcurrentImports System.LinqImports System.ThreadingImports System.Threading.TasksModule 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 SubEnd 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 expectedConstructors
| CountdownEvent(Int32) | Initializes a new instance of CountdownEvent class with the specified count. |
Properties
| CurrentCount | Gets the number of remaining signals required to set the event. |
| InitialCount | Gets the numbers of signals initially required to set the event. |
| IsSet | Indicates whether the CountdownEvent object's current count has reached zero. |
| WaitHandle | Gets a WaitHandle that is used to wait for the event to be set. |
Methods
| AddCount() | Increments the CountdownEvent's current count by one. |
| AddCount(Int32) | Increments the CountdownEvent's current count by a specified value. |
| Dispose() | Releases all resources used by the current instance of the CountdownEvent class. |
| Dispose(Boolean) | Releases the unmanaged resources used by the CountdownEvent, and optionally releases the managed resources. |
| Equals(Object) | Determines whether the specified object is equal to the current object. (Inherited from Object) |
| GetHashCode() | Serves as the default hash function. (Inherited from Object) |
| GetType() | Gets the Type of the current instance. (Inherited from Object) |
| MemberwiseClone() | Creates a shallow copy of the current Object. (Inherited from Object) |
| Reset() | Resets the CurrentCount to the value of InitialCount. |
| Reset(Int32) | Resets the InitialCount property to a specified value. |
| Signal() | Registers a signal with the CountdownEvent, decrementing the value of CurrentCount. |
| Signal(Int32) | Registers multiple signals with the CountdownEvent, decrementing the value of CurrentCount by the specified amount. |
| ToString() | Returns a string that represents the current object. (Inherited from Object) |
| TryAddCount() | Attempts to increment CurrentCount by one. |
| TryAddCount(Int32) | Attempts to increment CurrentCount by a specified value. |
| Wait() | Blocks the current thread until the CountdownEvent is set. |
| Wait(CancellationToken) | Blocks the current thread until the CountdownEvent is set, while observing a CancellationToken. |
| Wait(Int32) | Blocks the current thread until the CountdownEvent is set, using a 32-bit signed integer to measure the timeout. |
| Wait(Int32, CancellationToken) | Blocks the current thread until the CountdownEvent is set, using a 32-bit signed integer to measure the timeout, while observing a CancellationToken. |
| Wait(TimeSpan) | Blocks the current thread until the CountdownEvent is set, using a TimeSpan to measure the timeout. |
| Wait(TimeSpan, CancellationToken) | Blocks the current thread until the CountdownEvent is set, using a TimeSpan to measure the timeout, while observing a CancellationToken. |
Applies to
Thread Safety
All public and protected members of CountdownEvent are thread-safe and may be used concurrently from multiple threads, with the exception of Dispose(), which must only be used when all other operations on the CountdownEvent have completed, and Reset(), which should only be used when no other threads are accessing the event.
See also
- CountdownEvent
