كيفية القيام بما يلي: إضافة و أخذ العناصر بشكل فردي من BlockingCollection
يوضح هذا المثال كيفية إضافة وإزالة العناصر من BlockingCollection<T> في كلا الطريقتين الحظر و غير الحظر. لمزيد من المعلومات حول BlockingCollection<T> راجع نظرة عامة BlockingCollection.
للحصول على مثال عن كيفية تعداد BlockingCollection<T> حتى تصبح فارغة ولن يتم اضافة عناصر أخرى ، راجعكيفية القيام بما يلي: استخدم ForEach لإزالة عناصر في BlockingCollection
مثال
يوضح المثال الأول كيفية إضافة و التقاط العناصر كي تقوم العمليات بالحظر إذا كانت المجموعة فارغة بشكل مؤقت (اثناء التقاطها) أو عند وصولها للسعة القصوى (اثناء الإضافة) أو انقضاء مهلتها المحددة. لاحظ أن الحظر علي الحد الأقصى ممكّن فقط عندما يتم إنشاء BlockingCollection بحد أقصى تم تحديده في الدالة الانشائية.
Option Strict On
Option Explicit On
Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks
Module SimpleBlocking
Class Program
Shared Sub Main()
' Increase or decrease this value as desired.
Dim itemsToAdd As Integer = 500
' Preserve all the display output for Adds and Takes
Console.SetBufferSize(80, (itemsToAdd * 2) + 3)
' A bounded collection. Increase, decrease, or remove the
' maximum capacity argument to see how it impacts behavior.
Dim numbers = New BlockingCollection(Of Integer)(50)
' A simple blocking consumer with no cancellation.
Task.Factory.StartNew(Sub()
While numbers.IsCompleted = False
Dim i As Integer = numbers.Take()
Console.WriteLine("Take:{0} ", i)
' Simulate a slow consumer. This will cause
' collection to fill up fast and thus Adds wil block.
Thread.SpinWait(100000)
End While
Console.WriteLine(vbCrLf & "No more items to take. Press the Enter key to exit.")
End Sub)
' A simple blocking producer with no cancellation.
Task.Factory.StartNew(Sub()
For i As Integer = 0 To itemsToAdd
numbers.Add(i)
Console.WriteLine("Add:{0} Count={1}", i, numbers.Count)
Next
'See documentation for this method.
numbers.CompleteAdding()
End Sub)
'Keep the console window open in debug mode.
Console.ReadLine()
End Sub
End Class
End Module
namespace BCBlockingAccess
{
using System;
using System.Collections.Concurrent;
class Program
{
static void Main(string[] args)
{
// Increase or decrease this value as desired.
int itemsToAdd = 500;
// Preserve all the display output for Adds and Takes
Console.SetBufferSize(80, (itemsToAdd * 2) + 3);
// A bounded collection. Increase, decrease, or remove the
// maximum capacity argument to see how it impacts behavior.
BlockingCollection<int> numbers = new BlockingCollection<int>(50);
// A simple blocking consumer with no cancellation.
Task.Factory.StartNew(() =>
{
while (!numbers.IsCompleted)
{
int i = numbers.Take();
Console.WriteLine("Take:{0} ", i);
// Simulate a slow consumer. This will cause
// collection to fill up fast and thus Adds wil block.
Thread.SpinWait(100000);
}
Console.WriteLine("\r\nNo more items to take. Press the Enter key to exit.");
});
// A simple blocking producer with no cancellation.
Task.Factory.StartNew(() =>
{
for (int i = 0; i < itemsToAdd; i++)
{
numbers.Add(i);
Console.WriteLine("Add:{0} Count={1}", i, numbers.Count);
}
// See documentation for this method.
numbers.CompleteAdding();
});
// Keep the console display open in debug mode.
Console.ReadLine();
}
}
}
يوضح المثال الثاني كيفية إضافة وإلتقاط العناصر كي لا تقوم العمليات بالحظر. إذا لم يكن العنصر موجود أو تم بلوغ السعة القصوي للمجموعة المترابطة أو انقضت فترة المهلة له, فستقوم العملية TryAdd() أو TryTake() يإرجاع غير صحيح. وهذا يسمح لمؤشر الترابط بأن يقوم بأعمال أخرى مفيدة لبعض الوقت , ثم يحاول مرة أخرى لاحقاً أما استرداد عنصر جديد ,أو إضافة نفس العنصر الذي لم يستطع إضافته مسبقاً. كما يوضح البرنامج أيضا كيفية تطبيق الإلغاء عند الوصول إلى BlockingCollection<T>.
Option Strict On
Option Explicit On
Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks
Module NonBlockingBC
Class NonBlockingAccess
Shared inputs As Integer
Shared Sub Main()
' The token source for issuing the cancelation request.
Dim cts As CancellationTokenSource = New CancellationTokenSource()
' A blocking collection that can hold no more than 100 items at a time.
Dim numberCollection As BlockingCollection(Of Integer) = New BlockingCollection(Of Integer)(100)
' Set console buffer to hold our prodigious output.
Console.SetBufferSize(80, 2000)
' The simplest UI thread ever invented.
Task.Factory.StartNew(Sub()
If Console.ReadKey.KeyChar() = "c"c Then
cts.Cancel()
End If
End Sub)
' Start one producer and one consumer.
Task.Factory.StartNew(Sub() NonBlockingConsumer(numberCollection, cts.Token))
Task.Factory.StartNew(Sub() NonBlockingProducer(numberCollection, cts.Token))
Console.WriteLine("Press the Enter key to exit.")
Console.ReadLine()
End Sub
Shared Sub NonBlockingConsumer(ByVal bc As BlockingCollection(Of Integer), ByVal ct As CancellationToken)
' IsCompleted is equivalent to (IsAddingCompleted And Count = 0)
While bc.IsCompleted = False
Dim nextItem As Integer = 0
Try
If bc.TryTake(nextItem, 0, ct) Then
Console.WriteLine(" Take Blocked.")
Else
Console.WriteLine(" Take: {0}", nextItem)
End If
Catch ex As OperationCanceledException
Console.WriteLine("Taking canceled.")
Exit While
End Try
'Slow down consumer just a little to cause
' collection to fill up faster, and lead to "AddBlocked"
Thread.SpinWait(500000)
End While
Console.WriteLine(vbCrLf & "No more items to take. Press the Enter key to exit.")
End Sub
Shared Sub NonBlockingProducer(ByVal bc As BlockingCollection(Of Integer), ByVal ct As CancellationToken)
Dim itemToAdd As Integer = 0
Dim success As Boolean = False
Do While itemToAdd < inputs
'Cancellation causes OCE. We know how to handle it.
Try
success = bc.TryAdd(itemToAdd, 2, ct)
Catch ex As OperationCanceledException
Console.WriteLine("Add loop canceled.")
' Let other threads know we're done in case
' they aren't monitoring the cancellation token.
bc.CompleteAdding()
Exit Do
End Try
If success = True Then
Console.WriteLine(" Add:{0}", itemToAdd)
itemToAdd = itemToAdd + 1
Else
Console.Write(" AddBlocked:{0} Count = {1}", itemToAdd.ToString(), bc.Count)
' Don't increment nextItem. Try again on next iteration
' Do something else useful instead.
UpdateProgress(itemToAdd)
End If
Loop
End Sub
Shared Sub UpdateProgress(ByVal i As Integer)
Dim percent As Double = (CType(i, Double) / inputs) * 100
Console.WriteLine("Percent complete: {0}", percent)
End Sub
End Class
End Module
namespace BCNonBlockingWithCancellation
{
using System;
using System.Collections.Concurrent;
class ProgramWithCancellation
{
static int inputs = 2000;
static void Main(string[] args)
{
// The token source for issuing the cancelation request.
CancellationTokenSource cts = new CancellationTokenSource();
// A blocking collection that can hold no more than 100 items at a time.
BlockingCollection<int> numberCollection = new BlockingCollection<int>(100);
// Set console buffer to hold our prodigious output.
Console.SetBufferSize(80, 2000);
// The simplest UI thread ever invented.
Task.Factory.StartNew(() =>
{
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Start one producer and one consumer.
Task.Factory.StartNew(() => NonBlockingConsumer(numberCollection, cts.Token));
Task.Factory.StartNew(() => NonBlockingProducer(numberCollection, cts.Token));
Console.WriteLine("Press the Enter key to exit.");
Console.ReadLine();
}
static void NonBlockingConsumer(BlockingCollection<int> bc, CancellationToken ct)
{
// IsCompleted == (IsAddingCompleted && Count == 0)
while (!bc.IsCompleted)
{
int nextItem = 0;
try
{
if (!bc.TryTake(out nextItem, 0, ct))
{
Console.WriteLine(" Take Blocked");
}
else
Console.WriteLine(" Take:{0}", nextItem);
}
catch (OperationCanceledException)
{
Console.WriteLine("Taking canceled.");
break;
}
// Slow down consumer just a little to cause
// collection to fill up faster, and lead to "AddBlocked"
Thread.SpinWait(500000);
}
Console.WriteLine("\r\nNo more items to take. Press the Enter key to exit.");
}
static void NonBlockingProducer(BlockingCollection<int> bc, CancellationToken ct)
{
int itemToAdd = 0;
bool success = false;
do
{
// Cancellation causes OCE. We know how to handle it.
try
{
// A shorter timeout causes more failures.
success = bc.TryAdd(itemToAdd, 2, ct);
}
catch (OperationCanceledException)
{
Console.WriteLine("Add loop canceled.");
// Let other threads know we're done in case
// they aren't monitoring the cancellation token.
bc.CompleteAdding();
break;
}
if (success)
{
Console.WriteLine(" Add:{0}", itemToAdd);
itemToAdd++;
}
else
{
Console.Write(" AddBlocked:{0} Count = {1}", itemToAdd.ToString(), bc.Count);
// Don't increment nextItem. Try again on next iteration.
//Do something else useful instead.
UpdateProgress(itemToAdd);
}
} while (itemToAdd < inputs);
// No lock required here because only one producer.
bc.CompleteAdding();
}
static void UpdateProgress(int i)
{
double percent = ((double)i / inputs) * 100;
Console.WriteLine("Percent complete: {0}", percent);
}
}
}