How to: Use Parallel.Invoke to Execute Parallel Operations
This example shows how to parallelize operations by using Invoke in the Task Parallel Library. Three operations are performed on a shared data source. The operations can be executed in parallel in a straightforward manner, because none of them modifies the source.
Note
This documentation uses lambda expressions to define delegates in TPL. If you aren't familiar with lambda expressions in C# or Visual Basic, see Lambda Expressions in PLINQ and TPL.
Example
namespace ParallelTasks
{
using System;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
class ParallelInvoke
{
static void Main()
{
// Retrieve Goncharov's "Oblomov" from Gutenberg.org.
string[] words = CreateWordArray(@"http://www.gutenberg.org/files/54700/54700-0.txt");
#region ParallelTasks
// Perform three tasks in parallel on the source array
Parallel.Invoke(
() =>
{
Console.WriteLine("Begin first task...");
GetLongestWord(words);
}, // close first Action
() =>
{
Console.WriteLine("Begin second task...");
GetMostCommonWords(words);
}, //close second Action
() =>
{
Console.WriteLine("Begin third task...");
GetCountForWord(words, "sleep");
} //close third Action
); //close parallel.invoke
Console.WriteLine("Returned from Parallel.Invoke");
#endregion
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
#region HelperMethods
private static void GetCountForWord(string[] words, string term)
{
var findWord = from word in words
where word.ToUpper().Contains(term.ToUpper())
select word;
Console.WriteLine($@"Task 3 -- The word ""{term}"" occurs {findWord.Count()} times.");
}
private static void GetMostCommonWords(string[] words)
{
var frequencyOrder = from word in words
where word.Length > 6
group word by word into g
orderby g.Count() descending
select g.Key;
var commonWords = frequencyOrder.Take(10);
StringBuilder sb = new StringBuilder();
sb.AppendLine("Task 2 -- The most common words are:");
foreach (var v in commonWords)
{
sb.AppendLine(" " + v);
}
Console.WriteLine(sb.ToString());
}
private static string GetLongestWord(string[] words)
{
var longestWord = (from w in words
orderby w.Length descending
select w).First();
Console.WriteLine($"Task 1 -- The longest word is {longestWord}.");
return longestWord;
}
// An http request performed synchronously for simplicity.
static string[] CreateWordArray(string uri)
{
Console.WriteLine($"Retrieving from {uri}");
// Download a web page the easy way.
string s = new WebClient().DownloadString(uri);
// Separate string into an array of words, removing some common punctuation.
return s.Split(
new char[] { ' ', '\u000A', ',', '.', ';', ':', '-', '_', '/' },
StringSplitOptions.RemoveEmptyEntries);
}
#endregion
}
}
// The example displays output like the following:
// Retrieving from http://www.gutenberg.org/files/54700/54700-0.txt
// Begin first task...
// Begin second task...
// Begin third task...
// Task 2 -- The most common words are:
// Oblomov
// himself
// Schtoltz
// Gutenberg
// Project
// another
// thought
// Oblomov's
// nothing
// replied
//
// Task 1 -- The longest word is incomprehensible.
// Task 3 -- The word "sleep" occurs 57 times.
// Returned from Parallel.Invoke
// Press any key to exit
Imports System.Net
Imports System.Threading.Tasks
Module ParallelTasks
Sub Main()
' Retrieve Goncharov's "Oblomov" from Gutenberg.org.
Dim words As String() = CreateWordArray("http://www.gutenberg.org/files/54700/54700-0.txt")
'#Region "ParallelTasks"
' Perform three tasks in parallel on the source array
Parallel.Invoke(Sub()
Console.WriteLine("Begin first task...")
GetLongestWord(words)
' close first Action
End Sub,
Sub()
Console.WriteLine("Begin second task...")
GetMostCommonWords(words)
'close second Action
End Sub,
Sub()
Console.WriteLine("Begin third task...")
GetCountForWord(words, "sleep")
'close third Action
End Sub)
'close parallel.invoke
Console.WriteLine("Returned from Parallel.Invoke")
'#End Region
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
#Region "HelperMethods"
Sub GetCountForWord(ByVal words As String(), ByVal term As String)
Dim findWord = From word In words
Where word.ToUpper().Contains(term.ToUpper())
Select word
Console.WriteLine($"Task 3 -- The word ""{term}"" occurs {findWord.Count()} times.")
End Sub
Sub GetMostCommonWords(ByVal words As String())
Dim frequencyOrder = From word In words
Where word.Length > 6
Group By word
Into wordGroup = Group, Count()
Order By wordGroup.Count() Descending
Select wordGroup
Dim commonWords = From grp In frequencyOrder
Select grp
Take (10)
Dim s As String
s = "Task 2 -- The most common words are:" & vbCrLf
For Each v In commonWords
s = s & v(0) & vbCrLf
Next
Console.WriteLine(s)
End Sub
Function GetLongestWord(ByVal words As String()) As String
Dim longestWord = (From w In words
Order By w.Length Descending
Select w).First()
Console.WriteLine($"Task 1 -- The longest word is {longestWord}.")
Return longestWord
End Function
' An http request performed synchronously for simplicity.
Function CreateWordArray(ByVal uri As String) As String()
Console.WriteLine($"Retrieving from {uri}")
' Download a web page the easy way.
Dim s As String = New WebClient().DownloadString(uri)
' Separate string into an array of words, removing some common punctuation.
Return s.Split(New Char() {" "c, ControlChars.Lf, ","c, "."c, ";"c, ":"c,
"-"c, "_"c, "/"c}, StringSplitOptions.RemoveEmptyEntries)
End Function
#End Region
End Module
' The example displays output like the following:
' Retrieving from http://www.gutenberg.org/files/54700/54700-0.txt
' Begin first task...
' Begin second task...
' Begin third task...
' Task 2 -- The most common words are:
' Oblomov
' himself
' Schtoltz
' Gutenberg
' Project
' another
' thought
' Oblomov's
' nothing
' replied
'
' Task 1 -- The longest word is incomprehensible.
' Task 3 -- The word "sleep" occurs 57 times.
' Returned from Parallel.Invoke
' Press any key to exit
With Invoke, you simply express which actions you want to run concurrently, and the runtime handles all thread scheduling details, including scaling automatically to the number of cores on the host computer.
This example parallelizes the operations, not the data. As an alternate approach, you can parallelize the LINQ queries by using PLINQ and run the queries sequentially. Alternatively, you could parallelize the data by using PLINQ. Another option is to parallelize both the queries and the tasks. Although the resulting overhead might degrade performance on host computers with relatively few processors, it scales better on computers with many processors.
Compile the Code
Copy and paste the entire example into a Microsoft Visual Studio project and press F5.
See also
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