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Como: usar Parallel.Invoke para executar operações paralelas

  • Artigo

Este exemplo mostra como paralelizar operações usando Invoke na Biblioteca de paralelismo de tarefas. Três operações são executadas em uma fonte de dados compartilhada. As operações podem ser executadas em paralelo de uma maneira simples, pois nenhuma delas modifica a fonte.

Observação

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

Exemplo

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

Com Invoke, basta você expressar quais ações quer executar simultaneamente; o runtime manipula todos os detalhes de agendamento do thread, inclusive o dimensionamento automático para o número de núcleos no computador host.

Este exemplo paraleliza as operações, não os dados. Como uma abordagem alternativa, você pode paralelizar as consultas do LINQ usando PLINQ e executar as consultas em sequência. Como alternativa, você poderia paralelizar os dados usando o PLINQ. Outra opção é paralelizar as consultas e as tarefas. Embora a sobrecarga resultante possa degradar o desempenho em computadores host com relativamente poucos processadores, o dimensionamento é muito melhor em computadores com vários processadores.

Compile o código

Copie e cole o exemplo inteiro em um projeto do Microsoft Visual Studio e pressione F5.

Confira também