كيفية القيام بما يلي: استخدم ForEach لإزالة عناصر في BlockingCollection
بالإضافة إلى أخذ العناصر من BlockingCollection<T> باستخدام Take و الأسلوب TryTake() , يمكنك أيضاً استخدام foreach ( foreach في Visual Basic) للوصول إلى العناصر لحين إنتهاء الإضافة و حتى تصبح المجموعة فارغة.
مثال
المثال التالي يوضح كيفية تعداد كافة العناصر في BlockingCollection<T>.
Option Strict On
Option Explicit On
Imports System.Diagnostics
Imports System.Threading
Imports System.Threading.Tasks
Imports System.Collections.Concurrent
Module EnumerateBC
Class Program
' Limit the collection size to 2000 items
' at any given time. Set itemsToProduce to >500
' to hit the limit.
Const upperLimit As Integer = 1000
' Adjust this number to see how it impacts
' the producing-consuming pattern.
Const itemsToProduce As Integer = 100
Shared collection As BlockingCollection(Of Long) = New BlockingCollection(Of Long)(upperLimit)
' Variables for diagnostic output only.
Shared sw As New Stopwatch()
Shared totalAdditions As Integer = 0
' Counter for synchronizing producers.
Shared producersStillRunning As Integer = 2
Shared Sub Main()
' Start the stopwatch.
sw.Start()
' Queue the Producer threads.
Dim task1 = Task.Factory.StartNew(Sub() RunProducer("A", 0))
Dim task2 = Task.Factory.StartNew(Sub() RunProducer("B", itemsToProduce))
' Store in an array for use with ContinueWhenAll
Dim producers() As Task = {task1, task2}
' Create a cleanup task that will call CompleteAdding after
' all producers are done adding items.
Dim cleanup As Task = Task.Factory.ContinueWhenAll(producers, Sub(p) collection.CompleteAdding())
' Queue the Consumer thread. Put this call
' before Parallel.Invoke to begin consuming as soon as
' the producers add items.
Task.Factory.StartNew(Sub() RunConsumer())
' Keep the console window open while the
' consumer thread completes its output.
Console.ReadKey()
End Sub
Shared Sub RunProducer(ByVal ID As String, ByVal start As Integer)
Dim additions As Integer = 0
For i As Integer = start To start + itemsToProduce - 1
' The data that is added to the collection.
Dim ticks As Long = sw.ElapsedTicks
'Display additions and subtractions.
Console.WriteLine("{0} adding tick value {1}. item# {2}", ID, ticks, i)
' Don't try to add item after CompleteAdding
' has been called.
If collection.IsAddingCompleted = False Then
collection.Add(ticks)
End If
' Counter for demonstration purposes only.
additions = additions + 1
' Uncomment this line to
' slow down the producer threads without sleeping.
Thread.SpinWait(100000)
Next
Interlocked.Add(totalAdditions, additions)
Console.WriteLine("{0} is done adding: {1} items", ID, additions)
End Sub
Shared Sub RunConsumer()
' GetConsumingEnumerable returns the enumerator for the
' underlying collection.
Dim subtractions As Integer = 0
For Each item In collection.GetConsumingEnumerable
subtractions = subtractions + 1
Console.WriteLine("Consuming tick value {0} : item# {1} : current count = {2}",
item.ToString("D18"), subtractions, collection.Count)
Next
Console.WriteLine("Total added: {0} Total consumed: {1} Current count: {2} ",
totalAdditions, subtractions, collection.Count())
sw.Stop()
Console.WriteLine("Press any key to exit.")
End Sub
End Class
End Module
namespace EnumerateBlockingCollection
{
using System;
using System.Collections.Concurrent;
using System.Diagnostics;
class Program
{
// Limit the collection size to 2000 items
// at any given time. Set itemsToProduce to >500
// to hit the limit.
const int upperLimit = 1000;
// Adjust this number to see how it impacts
// the producing-consuming pattern.
const int itemsToProduce = 100;
static BlockingCollection<long> collection = new BlockingCollection<long>(upperLimit);
// Variables for diagnostic output only.
static Stopwatch sw = new Stopwatch();
static int totalAdditions = 0;
// Counter for synchronizing producers.
static int producersStillRunning = 2;
static void Main(string[] args)
{
// Start the stopwatch.
sw.Start();
// Queue the Producer threads. Store in an array
// for use with ContinueWhenAll
Task[] producers = new Task[2];
producers[0] = Task.Factory.StartNew(() => RunProducer("A", 0));
producers[1] = Task.Factory.StartNew(() => RunProducer("B", itemsToProduce));
// Create a cleanup task that will call CompleteAdding after
// all producers are done adding items.
Task cleanup = Task.Factory.ContinueWhenAll(producers, (p) => collection.CompleteAdding());
// Queue the Consumer thread. Put this call
// before Parallel.Invoke to begin consuming as soon as
// the producers add items.
Task.Factory.StartNew(() => RunConsumer());
// Keep the console window open while the
// consumer thread completes its output.
Console.ReadKey();
}
static void RunProducer(string ID, int start)
{
int additions = 0;
for (int i = start; i < start + itemsToProduce; i++)
{
// The data that is added to the collection.
long ticks = sw.ElapsedTicks;
// Display additions and subtractions.
Console.WriteLine("{0} adding tick value {1}. item# {2}", ID, ticks, i);
if(!collection.IsAddingCompleted)
collection.Add(ticks);
// Counter for demonstration purposes only.
additions++;
// Uncomment this line to
// slow down the producer threads ing.
Thread.SpinWait(100000);
}
Interlocked.Add(ref totalAdditions, additions);
Console.WriteLine("{0} is done adding: {1} items", ID, additions);
}
static void RunConsumer()
{
// GetConsumingEnumerable returns the enumerator for the
// underlying collection.
int subtractions = 0;
foreach (var item in collection.GetConsumingEnumerable())
{
Console.WriteLine("Consuming tick value {0} : item# {1} : current count = {2}",
item.ToString("D18"), subtractions++, collection.Count);
}
Console.WriteLine("Total added: {0} Total consumed: {1} Current count: {2} ",
totalAdditions, subtractions, collection.Count());
sw.Stop();
Console.WriteLine("Press any key to exit");
}
}
}
System.Collections.Concurrent.BlockingCollection<T> يحدد الحد الأقصى لعدد العناصر الموجودة في المجموعة في أي وقت. تعداد المجموعة مع foreach ( For Each في Visual Basic) يحظر الدالة الخيطية الخاصة بالمستهلك إذا لم تتوفر أية عناصر. يستخدم هذا المثال foreach تكرار حلقي مع الأسلوب BlockingCollection<T>.GetConsumingEnumerable في الدالة الخيطية المستهلكة. هذا النوع من التكرار الحلقي يتوقف إذا كانت المجموعة فارغة. في هذا المثال الحظر ليس مهماً لأن الدالة الخيطية المنتجة تضيف العناصر أسرع مما يمكن استهلاكها.
ليس هناك أي ضمان بأن يتم تعداد العناصر بنفس الترتيب الذي تمت إضافتها به بواسطة الدوال الخيطية المنتجة.