Como: Usar Parallel. Invoke para executar operações paralelas

Artigo
08/01/2011

Este exemplo mostra como paralelizar as operações usando ParallelInvoke() na biblioteca paralela de tarefas. Três operações são executadas em uma fonte de dados compartilhados. Porque nenhuma das operações modifica a fonte, eles podem ser executados em paralelo de forma direta.

Observação

Esta documentação usa expressões lambda para definir os delegados na TPL.Se você não estiver familiarizado com as expressões lambda em C# ou Visual Basic, consulte Expressões lambda no PLINQ e TPL.

Exemplo

' How to: Use Parallel.Invoke to Execute Parallel Operations
Option Explicit On
Option Strict On

Imports System.Threading.Tasks
Imports System.Net

Module ParallelTasks

    Sub Main()
        ' Retrieve Darwin's "Origin of the Species" from Gutenberg.org.
        Dim words As String() = CreateWordArray("http://www.gutenberg.org/files/2009/2009.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, "species")
                '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 ""{0}"" occurs {1} times.", term, findWord.Count())
    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 {0}", longestWord)
        Return longestWord
    End Function


    ' An http request performed synchronously for simplicity.
    Function CreateWordArray(ByVal uri As String) As String()
        Console.WriteLine("Retrieving from {0}", 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


    ' Output (May vary on each execution):
    ' Retrieving from http://www.gutenberg.org/dirs/etext99/otoos610.txt
    ' Response stream received.
    ' Begin first task...
    ' Begin second task...
    ' Task 2 -- The most common words are:
    ' species
    ' selection
    ' varieties
    ' natural
    ' animals
    ' between
    ' different
    ' distinct
    ' several
    ' conditions
    '
    ' Begin third task...
    ' Task 1 -- The longest word is characteristically
    ' Task 3 -- The word "species" occurs 1927 times.
    ' Returned from Parallel.Invoke
    ' Press any key to exit 
    ' 
End Module

namespace ParallelTasks
{
    using System;
    using System.IO;
    using System.Linq;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    using System.Net;

    class ParallelInvoke
    {
        static void Main()
        {
            // Retrieve Darwin's "Origin of the Species" from Gutenberg.org.
            string[] words = CreateWordArray(@"http://www.gutenberg.org/files/2009/2009.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, "species");
                             } //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 ""{0}"" occurs {1} times.",
                term, findWord.Count());
        }

        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 {0}", longestWord);
            return longestWord;
        }


        // An http request performed synchronously for simplicity.
        static string[] CreateWordArray(string uri)
        {
            Console.WriteLine("Retrieving from {0}", 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
    }

    /* Output (May vary on each execution):
        Retrieving from http://www.gutenberg.org/dirs/etext99/otoos610.txt
        Response stream received.
        Begin first task...
        Begin second task...
        Task 2 -- The most common words are:
          species
          selection
          varieties
          natural
          animals
          between
          different
          distinct
          several
          conditions

        Begin third task...
        Task 1 -- The longest word is characteristically
        Task 3 -- The word "species" occurs 1927 times.
        Returned from Parallel.Invoke
        Press any key to exit  
     */
}

Observe que com Invoke(), simplesmente express que ações você deseja executar simultaneamente e o tempo de execução lida com todos os segmentos de agendamento de detalhes, incluindo o dimensionamento automaticamente para o número de núcleos no computador host.

Este exemplo parallelizes as operações, não os dados. Como uma abordagem alternativa, você pode paralelizar as consultas LINQ usando PLINQ e executar consultas seqüencialmente. Como alternativa, você poderia paralelizar os dados usando PLINQ. Outra opção é paralelizar as consultas e tarefas. Embora o resultante sobrecarga pode prejudicar o desempenho em computadores de host com relativamente poucas processadores, ele fosse capaz de crescer muito melhor em computadores com vários processadores.