当 For() 循环的循环体很小时，它的执行速度可能比等效的顺序循环更慢。 对数据进行分区所涉及的开销以及调用每个循环迭代上的委托的开销导致了性能降低。 为了解决类似情况，Partitioner 类提供 Create 方法，该方法使您可以为委托体提供顺序循环，以便每个分区只调用一次委托，而不是每个迭代调用一次委托。 有关更多信息，请参见 PLINQ 和 TPL 的自定义分区程序。
示例
Imports System.Threading.Tasks
Imports System.Collections.Concurrent
Module PartitionDemo
Sub Main()
' Source must be array or IList.
Dim source = Enumerable.Range(0, 100000).ToArray()
' Partition the entire source array.
' Let the partitioner size the ranges.
Dim rangePartitioner = Partitioner.Create(0, source.Length)
Dim results(source.Length - 1) As Double
' Loop over the partitions in parallel. The Sub is invoked
' once per partition.
Parallel.ForEach(rangePartitioner, Sub(range, loopState)
' Loop over each range element without a delegate invocation.
For i As Integer = range.Item1 To range.Item2 - 1
results(i) = source(i) * Math.PI
Next
End Sub)
Console.WriteLine("Operation complete. Print results? y/n")
Dim input As Char = Console.ReadKey().KeyChar
If input = "y"c Or input = "Y"c Then
For Each d As Double In results
Console.Write("{0} ", d)
Next
End If
End Sub
End Module
using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
class Program
{
static void Main()
{
// Source must be array or IList.
var source = Enumerable.Range(0, 100000).ToArray();
// Partition the entire source array.
var rangePartitioner = Partitioner.Create(0, source.Length);
double[] results = new double[source.Length];
// Loop over the partitions in parallel.
Parallel.ForEach(rangePartitioner, (range, loopState) =>
{
// Loop over each range element without a delegate invocation.
for (int i = range.Item1; i < range.Item2; i++)
{
results[i] = source[i] * Math.PI;
}
});
Console.WriteLine("Operation complete. Print results? y/n");
char input = Console.ReadKey().KeyChar;
if (input == 'y' || input == 'Y')
{
foreach(double d in results)
{
Console.Write("{0} ", d);
}
}
}
}
本示例中演示的方法在循环执行极少量工作时非常有用。 当工作变为需要消耗更大量计算资源时，通过将 For 或 ForEach 循环与默认分区程序一起使用可能会获得相同或者更好的性能。