如何:在 PLINQ 中指定合并选项
此示例展示了如何指定应用于 PLINQ 查询中所有后续运算符的合并选项。 虽然无需显式设置合并选项,但这样做可以提升性能。 若要详细了解合并选项,请参阅 PLINQ 中的合并选项。
警告
本示例旨在演示用法,运行速度可能不如等效的顺序 LINQ to Objects 查询快。 若要详细了解加速,请参阅了解 PLINQ 中的加速。
示例
下面的示例展示了合并选项在基本方案中的行为,此方案包含无序源,并将高成本函数应用于每个元素。
namespace MergeOptions
{
using System;
using System.Diagnostics;
using System.Linq;
using System.Threading;
class Program
{
static void Main(string[] args)
{
var nums = Enumerable.Range(1, 10000);
// Replace NotBuffered with AutoBuffered
// or FullyBuffered to compare behavior.
var scanLines = from n in nums.AsParallel()
.WithMergeOptions(ParallelMergeOptions.NotBuffered)
where n % 2 == 0
select ExpensiveFunc(n);
Stopwatch sw = Stopwatch.StartNew();
foreach (var line in scanLines)
{
Console.WriteLine(line);
}
Console.WriteLine("Elapsed time: {0} ms. Press any key to exit.",
sw.ElapsedMilliseconds);
Console.ReadKey();
}
// A function that demonstrates what a fly
// sees when it watches television :-)
static string ExpensiveFunc(int i)
{
Thread.SpinWait(2000000);
return string.Format("{0} *****************************************", i);
}
}
}
Class MergeOptions2
Sub DoMergeOptions()
Dim nums = Enumerable.Range(1, 10000)
' Replace NotBuffered with AutoBuffered
' or FullyBuffered to compare behavior.
Dim scanLines = From n In nums.AsParallel().WithMergeOptions(ParallelMergeOptions.NotBuffered)
Where n Mod 2 = 0
Select ExpensiveFunc(n)
Dim sw = Stopwatch.StartNew()
For Each line In scanLines
Console.WriteLine(line)
Next
Console.WriteLine("Elapsed time: {0} ms. Press any key to exit.")
Console.ReadKey()
End Sub
' A function that demonstrates what a fly
' sees when it watches television :-)
Function ExpensiveFunc(ByVal i As Integer) As String
Threading.Thread.SpinWait(2000000)
Return String.Format("{0} *****************************************", i)
End Function
End Class
如果 AutoBuffered 选项在第一个元素生成前导致不利延迟发生,请尝试使用 NotBuffered 选项,更快更顺畅地生成结果元素。