HOW TO：使用 ConcurrentBag 建立物件集區
這個範例示範如何使用並行 Bag 實作物件集區。 在您需要多個類別執行個體，而建立或終結類別較昂貴時，物件集區可以改善應用程式效能。 當用戶端程式要求新物件時，物件集區會先嘗試提供已建立並傳回至集區的物件。 如果沒有可用的物件，才會建立新物件。
ConcurrentBag<T> 可用來儲存物件，因為它支援快速插入和移除，尤其是相同執行緒同時加入和移除項目時。 這個範例可進一步擴大針對 Bag 資料結構實作的 IProducerConsumerCollection<T> 建置，就如同 ConcurrentQueue<T> 和 ConcurrentStack<T>。
範例
Imports System
Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks
Module ObjectPoolExample
Public Class ObjectPool(Of T)
Private _objects As ConcurrentBag(Of T)
Private _objectGenerator As Func(Of T)
Public Sub New(ByVal objectGenerator As Func(Of T))
If objectGenerator Is Nothing Then Throw New ArgumentNullException("objectGenerator")
_objects = New ConcurrentBag(Of T)()
_objectGenerator = objectGenerator
End Sub
Public Function GetObject() As T
Dim item As T
If _objects.TryTake(item) Then Return item
Return _objectGenerator()
End Function
Public Sub PutObject(ByVal item As T)
_objects.Add(item)
End Sub
End Class
Sub Main()
Dim cts As CancellationTokenSource = New CancellationTokenSource()
' Create an opportunity for the user to cancel.
Task.Factory.StartNew(Sub()
If Console.ReadKey().KeyChar = "c"c Or Console.ReadKey().KeyChar = "C"c Then
cts.Cancel()
End If
End Sub)
Dim pool As ObjectPool(Of TestClass) = New ObjectPool(Of TestClass)(Function() New TestClass())
' Create a high demand for TestClass objects.
Parallel.For(0, 1000000, Sub(i, loopState)
Dim mc As TestClass = pool.GetObject()
Console.CursorLeft = 0
' This is the bottleneck in our application. All threads in this loop
' must serialize their access to the static Console class.
Console.WriteLine("{0:####.####}", mc.GetValue(i))
pool.PutObject(mc)
If cts.Token.IsCancellationRequested Then
loopState.Stop()
End If
End Sub)
Console.WriteLine("Press the Enter key to exit.")
Console.ReadLine()
End Sub
' A toy class that requires some resources to create.
' You can experiment here to measure the performance of the
' object pool vs. ordinary instantiation.
Class TestClass
Public Nums() As Integer
Public Function GetValue(ByVal i As Long) As Double
Return Math.Sqrt(Nums(i))
End Function
Public Sub New()
Nums = New Integer(10000000) {}
' ReDim Nums(1000000)
Dim rand As Random = New Random()
For i As Integer = 0 To Nums.Length - 1
Nums(i) = rand.Next()
Next
End Sub
End Class
End Module
using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
namespace ObjectPoolExample
{
public class ObjectPool<T>
{
private ConcurrentBag<T> _objects;
private Func<T> _objectGenerator;
public ObjectPool(Func<T> objectGenerator)
{
if (objectGenerator == null) throw new ArgumentNullException("objectGenerator");
_objects = new ConcurrentBag<T>();
_objectGenerator = objectGenerator;
}
public T GetObject()
{
T item;
if (_objects.TryTake(out item)) return item;
return _objectGenerator();
}
public void PutObject(T item)
{
_objects.Add(item);
}
}
class Program
{
static void Main(string[] args)
{
CancellationTokenSource cts = new CancellationTokenSource();
// Create an opportunity for the user to cancel.
Task.Factory.StartNew(() =>
{
if (Console.ReadKey().KeyChar == 'c' || Console.ReadKey().KeyChar == 'C')
cts.Cancel();
});
ObjectPool<MyClass> pool = new ObjectPool<MyClass> (() => new MyClass());
// Create a high demand for MyClass objects.
Parallel.For(0, 1000000, (i, loopState) =>
{
MyClass mc = pool.GetObject();
Console.CursorLeft = 0;
// This is the bottleneck in our application. All threads in this loop
// must serialize their access to the static Console class.
Console.WriteLine("{0:####.####}", mc.GetValue(i));
pool.PutObject(mc);
if (cts.Token.IsCancellationRequested)
loopState.Stop();
});
Console.WriteLine("Press the Enter key to exit.");
Console.ReadLine();
}
}
// A toy class that requires some resources to create.
// You can experiment here to measure the performance of the
// object pool vs. ordinary instantiation.
class MyClass
{
public int[] Nums {get; set;}
public double GetValue(long i)
{
return Math.Sqrt(Nums[i]);
}
public MyClass()
{
Nums = new int[1000000];
Random rand = new Random();
for (int i = 0; i < Nums.Length; i++)
Nums[i] = rand.Next();
}
}
}