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Création de threads et passage de données au démarrage

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Mise à jour : novembre 2007

Lors de la création d'un processus de système d'exploitation, le système d'exploitation injecte un thread pour exécuter du code dans ce processus, y compris tout domaine d'application d'origine. À partir de là, des domaines d'application peuvent être créés et détruits sans nécessairement créer ou détruire des threads de système d'exploitation. Si le code en cours d'exécution est du code géré, un objet Thread pour le thread s'exécutant dans le domaine d'application en cours peut être obtenu en récupérant la propriété statique CurrentThread de type Thread. Cette rubrique décrit la création de thread et présente des alternatives pour passer des données à la procédure de thread.

Création d'un thread

La création d'un objet Thread crée un thread managé. La classe Thread a des constructeurs qui prennent un délégué ThreadStart ou un délégué ParameterizedThreadStart ; le délégué encapsule la méthode qui est appelée par le nouveau thread lorsque vous appelez la méthode Start. Plusieurs appels Start entraînent la levée d'une ThreadStateException.

La méthode Start retourne immédiatement, souvent avant que le nouveau thread ait réellement commencé. Vous pouvez utiliser les propriétés ThreadState et IsAlive pour déterminer l'état du thread à tout moment, mais ces propriétés ne doivent jamais être utilisées pour synchroniser les activités de threads.

Remarque :

Une fois qu'un thread est démarré, il est inutile de conserver une référence à l'objet Thread. L'exécution du thread se poursuit jusqu'à ce que la procédure de thread soit terminée.

L'exemple de code suivant crée deux nouveaux threads pour appeler des méthodes statiques et d'instance sur un autre objet.

Imports System
Imports System.Threading

Public Class ServerClass

    ' The method that will be called when the thread is started.
    Public Sub InstanceMethod()
        Console.WriteLine( _
            "ServerClass.InstanceMethod is running on another thread.")

        ' Pause for a moment to provide a delay to make 
        ' threads more apparent.
        Thread.Sleep(3000) 
        Console.WriteLine( _
            "The instance method called by the worker thread has ended.")
    End Sub 'InstanceMethod

    Public Shared Sub StaticMethod()
        Console.WriteLine( _
            "ServerClass.StaticMethod is running on another thread.")

        ' Pause for a moment to provide a delay to make 
        ' threads more apparent.
        Thread.Sleep(5000) 
        Console.WriteLine( _
            "The static method called by the worker thread has ended.")
    End Sub 'StaticMethod
End Class 'ServerClass

Public Class Simple

    Public Shared Sub Main() 
        Console.WriteLine("Thread Simple Sample")

        Dim serverObject As New ServerClass()

        ' Create the thread object, passing in the 
        ' serverObject.InstanceMethod method using a
        ' ThreadStart delegate.
        Dim InstanceCaller As New Thread( _
            New ThreadStart(AddressOf serverObject.InstanceMethod))

        ' Start the thread.
        InstanceCaller.Start()

        Console.WriteLine("The Main() thread calls this after " _
            & "starting the new InstanceCaller thread.")

        ' Create the thread object, passing in the 
        ' serverObject.StaticMethod method using a 
        ' ThreadStart delegate.
        Dim StaticCaller As New Thread( _
            New ThreadStart(AddressOf ServerClass.StaticMethod))

        ' Start the thread.
        StaticCaller.Start()

        Console.WriteLine("The Main() thread calls this after " _
            & "starting the new StaticCaller thread.")

    End Sub 'Main
End Class 'Simple

using System;
using System.Threading;

public class ServerClass
{
    // The method that will be called when the thread is started.
    public void InstanceMethod()
    {
        Console.WriteLine(
            "ServerClass.InstanceMethod is running on another thread.");

        // Pause for a moment to provide a delay to make 
        // threads more apparent.
        Thread.Sleep(3000);
        Console.WriteLine(
            "The instance method called by the worker thread has ended.");
    }

    public static void StaticMethod()
    {
        Console.WriteLine(
            "ServerClass.StaticMethod is running on another thread.");

        // Pause for a moment to provide a delay to make 
        // threads more apparent.
        Thread.Sleep(5000);
        Console.WriteLine(
            "The static method called by the worker thread has ended.");
    }
}

public class Simple{
    public static int Main(String[] args)
    {
        Console.WriteLine("Thread Simple Sample");

        ServerClass serverObject = new ServerClass();

        // Create the thread object, passing in the 
        // serverObject.InstanceMethod method using a 
        // ThreadStart delegate.
        Thread InstanceCaller = new Thread(
            new ThreadStart(serverObject.InstanceMethod));

        // Start the thread.
        InstanceCaller.Start();

        Console.WriteLine("The Main() thread calls this after " 
            + "starting the new InstanceCaller thread.");

        // Create the thread object, passing in the 
        // serverObject.StaticMethod method using a 
        // ThreadStart delegate.
        Thread StaticCaller = new Thread(
            new ThreadStart(ServerClass.StaticMethod));

        // Start the thread.
        StaticCaller.Start();

        Console.WriteLine("The Main() thread calls this after "
            + "starting the new StaticCaller thread.");

        return 0;
    }
}

using namespace System;
using namespace System::Threading;

public ref class ServerClass
{
public:

    // The method that will be called when the thread is started.
    void InstanceMethod()
    {
        Console::WriteLine(
            "ServerClass->InstanceMethod is running on another thread.");

        // Pause for a moment to provide a delay to make 
        // threads more apparent.
        Thread::Sleep(3000);
        Console::WriteLine(
            "The instance method called by the worker thread has ended.");
    }

    static void StaticMethod()
    {
        Console::WriteLine(
            "ServerClass::StaticMethod is running on another thread.");

        // Pause for a moment to provide a delay to make 
        // threads more apparent.
        Thread::Sleep(5000);
        Console::WriteLine(
            "The static method called by the worker thread has ended.");
    }
};

void main()
{
    Console::WriteLine("Thread Simple Sample");

    ServerClass^ serverObject = gcnew ServerClass();

    // Create the thread object, passing in a ThreadStart delegate
    // representing an instance of ServerClass and the 
    // ServerClass::InstanceMethod method.
    Thread^ InstanceCaller = gcnew Thread(
        gcnew ThreadStart(serverObject, &ServerClass::InstanceMethod));

    // Start the thread.
    InstanceCaller->Start();

    Console::WriteLine("The main thread has " 
        + "started the new InstanceMethod thread.");

    // Create the thread object, passing in a ThreadStart delegate 
    // representing the static ServerClass::StaticMethod method.
    Thread^ StaticCaller = gcnew Thread(
        gcnew ThreadStart(&ServerClass::StaticMethod));

    // Start the thread.
    StaticCaller->Start();

    Console::WriteLine("The main thread has called "
        + "the new StaticMethod thread.");
}

Passage de données aux threads et récupération de données à partir de threads

Dans le .NET Framework version 2.0, le délégué ParameterizedThreadStart offre un moyen facile de passer un objet contenant des données à un thread lorsque vous appelez la surcharge de méthode Thread.Start. Consultez ParameterizedThreadStart pour obtenir un exemple de code.

L'utilisation du délégué ParameterizedThreadStart n'est pas une manière sécurisée de passer des données parce que la surcharge de méthode Thread.Start accepte n'importe quel objet. Une alternative consiste à encapsuler la procédure de thread et les données dans une classe d'assistance et à utiliser le délégué ThreadStart pour exécuter la procédure de thread. Cette technique est montrée dans les deux exemples de code qui suivent.

Aucun de ces délégués n'a de valeur de retour parce qu'il n'y a pas de place pour retourner les données provenant d'un appel asynchrone. Pour récupérer les résultats d'une méthode de thread, vous pouvez utiliser une méthode de rappel comme démontré dans le deuxième exemple de code.

Imports System
Imports System.Threading

' The ThreadWithState class contains the information needed for
' a task, and the method that executes the task.
'
Public Class ThreadWithState
    ' State information used in the task.
    Private boilerplate As String
    Private value As Integer

    ' The constructor obtains the state information.
    Public Sub New(ByVal text As String, ByVal number As Integer)
        boilerplate = text
        value = number
    End Sub

    ' The thread procedure performs the task, such as formatting 
    ' and printing a document.
    Public Sub ThreadProc()
        Console.WriteLine(boilerplate, value) 
    End Sub
End Class

' Entry point for the example.
'
Public Class Example
    Public Shared Sub Main()

        ' Supply the state information required by the task.
        Dim tws As New ThreadWithState( _
            "This report displays the number {0}.", 42)

        ' Create a thread to execute the task, and then
        ' start the thread.
        Dim t As New Thread(AddressOf tws.ThreadProc)
        t.Start()
        Console.WriteLine("Main thread does some work, then waits.")
        t.Join()
        Console.WriteLine( _
            "Independent task has completed; main thread ends.")  
    End Sub
End Class

using System;
using System.Threading;

// The ThreadWithState class contains the information needed for
// a task, and the method that executes the task.
//
public class ThreadWithState {
    // State information used in the task.
    private string boilerplate;
    private int value;

    // The constructor obtains the state information.
    public ThreadWithState(string text, int number) 
    {
        boilerplate = text;
        value = number;
    }

    // The thread procedure performs the task, such as formatting 
    // and printing a document.
    public void ThreadProc() 
    {
        Console.WriteLine(boilerplate, value); 
    }
}

// Entry point for the example.
//
public class Example {
    public static void Main() 
    {
        // Supply the state information required by the task.
        ThreadWithState tws = new ThreadWithState(
            "This report displays the number {0}.", 42);

        // Create a thread to execute the task, and then
        // start the thread.
        Thread t = new Thread(new ThreadStart(tws.ThreadProc));
        t.Start();
        Console.WriteLine("Main thread does some work, then waits.");
        t.Join();
        Console.WriteLine(
            "Independent task has completed; main thread ends.");  
    }
}

using namespace System;
using namespace System::Threading;

// The ThreadWithState class contains the information needed for
// a task, and the method that executes the task.
//
public ref class ThreadWithState 
{
private:
    // State information used in the task.
    String^ boilerplate;
    int value;

public:
    // The constructor obtains the state information.
    ThreadWithState(String^ text, int number) 
    {
        boilerplate = text;
        value = number;
    }

    // The thread procedure performs the task, such as formatting 
    // and printing a document.
    void ThreadProc() 
    {
        Console::WriteLine(boilerplate, value); 
    }
};

// Entry point for the example.
//
void main() 
{
    // Supply the state information required by the task.
    ThreadWithState^ tws = gcnew ThreadWithState(
        "This report displays the number {0}.", 42);

    // Create a thread to execute the task, and then
    // start the thread.
    Thread^ t = gcnew Thread(
        gcnew ThreadStart(tws, &ThreadWithState::ThreadProc));
    t->Start();
    Console::WriteLine("Main thread does some work, then waits.");
    t->Join();
    Console::WriteLine(
        "Independent task has completed; main thread ends.");  
}

Récupération de données avec les méthodes de rappel

L'exemple suivant illustre une méthode de rappel qui récupère des données d'un thread. Le constructeur de la classe qui contient les données et la méthode de thread accepte également un délégué représentant la méthode de rappel ; avant la fin de la méthode de thread, il appelle le délégué de rappel.

Imports System
Imports System.Threading

' The ThreadWithState class contains the information needed for
' a task, the method that executes the task, and a delegate
' to call when the task is complete.
'
Public Class ThreadWithState
    ' State information used in the task.
    Private boilerplate As String
    Private value As Integer

    ' Delegate used to execute the callback method when the
    ' task is complete.
    Private callback As ExampleCallback

    ' The constructor obtains the state information and the
    ' callback delegate.
    Public Sub New(ByVal text As String, ByVal number As Integer, _
                   ByVal callbackDelegate As ExampleCallback)
        boilerplate = text
        value = number
        callback = callbackDelegate
    End Sub

    ' The thread procedure performs the task, such as
    ' formatting and printing a document, and then invokes
    ' the callback delegate with the number of lines printed.
    Public Sub ThreadProc()
        Console.WriteLine(boilerplate, value) 
        If Not callback Is Nothing Then callback(1)
    End Sub
End Class

' Delegate that defines the signature for the callback method.
'
Public Delegate Sub ExampleCallback(ByVal lineCount As Integer)

' Entry point for the example.
'
Public Class Example
    Public Shared Sub Main()
        ' Supply the state information required by the task.
        Dim tws As New ThreadWithState( _
            "This report displays the number {0}.", _
            42, _
            New ExampleCallback(AddressOf ResultCallback) _
        )

        Dim t As New Thread(AddressOf tws.ThreadProc)
        t.Start()
        Console.WriteLine("Main thread does some work, then waits.")
        t.Join()
        Console.WriteLine( _
            "Independent task has completed; main thread ends.")  
    End Sub

    ' The callback method must match the signature of the
    ' callback delegate.
    '
    Public Shared Sub ResultCallback(ByVal lineCount As Integer)
        Console.WriteLine("Independent task printed {0} lines.", _
            lineCount)  
    End Sub
End Class

using System;
using System.Threading;

// The ThreadWithState class contains the information needed for
// a task, the method that executes the task, and a delegate
// to call when the task is complete.
//
public class ThreadWithState {
    // State information used in the task.
    private string boilerplate;
    private int value;

    // Delegate used to execute the callback method when the
    // task is complete.
    private ExampleCallback callback;

    // The constructor obtains the state information and the
    // callback delegate.
    public ThreadWithState(string text, int number, 
        ExampleCallback callbackDelegate) 
    {
        boilerplate = text;
        value = number;
        callback = callbackDelegate;
    }
    
    // The thread procedure performs the task, such as
    // formatting and printing a document, and then invokes
    // the callback delegate with the number of lines printed.
    public void ThreadProc() 
    {
        Console.WriteLine(boilerplate, value);
        if (callback != null)
            callback(1);
    }
}

// Delegate that defines the signature for the callback method.
//
public delegate void ExampleCallback(int lineCount);

// Entry point for the example.
//
public class Example 
{
    public static void Main() 
    {
        // Supply the state information required by the task.
        ThreadWithState tws = new ThreadWithState(
            "This report displays the number {0}.",
            42,
            new ExampleCallback(ResultCallback)
        );

        Thread t = new Thread(new ThreadStart(tws.ThreadProc));
        t.Start();
        Console.WriteLine("Main thread does some work, then waits.");
        t.Join();
        Console.WriteLine(
            "Independent task has completed; main thread ends."); 
    }

    // The callback method must match the signature of the
    // callback delegate.
    //
    public static void ResultCallback(int lineCount) 
    {
        Console.WriteLine(
            "Independent task printed {0} lines.", lineCount);
    }
}

using namespace System;
using namespace System::Threading;

// Delegate that defines the signature for the callback method.
//
public delegate void ExampleCallback(int lineCount);

// The ThreadWithState class contains the information needed for
// a task, the method that executes the task, and a delegate
// to call when the task is complete.
//
public ref class ThreadWithState 
{
private:
    // State information used in the task.
    String^ boilerplate;
    int value;

    // Delegate used to execute the callback method when the
    // task is complete.
    ExampleCallback^ callback;

public:
    // The constructor obtains the state information and the
    // callback delegate.
    ThreadWithState(String^ text, int number, 
        ExampleCallback^ callbackDelegate)  
    {
        boilerplate = text;
        value = number;
        callback = callbackDelegate;
    }

    // The thread procedure performs the task, such as
    // formatting and printing a document, and then invokes
    // the callback delegate with the number of lines printed.
    void ThreadProc() 
    {
        Console::WriteLine(boilerplate, value); 
        if (callback != nullptr)
            callback(1);
    }
};

public ref class Example
{
public:
    static void Demo()
    {
        // Supply the state information required by the task.
        ThreadWithState^ tws = gcnew ThreadWithState(
            "This report displays the number {0}.",
            42,
            gcnew ExampleCallback(&Example::ResultCallback)
        );

        // Create a thread to execute the task, and then
        // start the thread.
        Thread^ t = gcnew Thread(
            gcnew ThreadStart(tws, &ThreadWithState::ThreadProc));
        t->Start();
        Console::WriteLine("Main thread does some work, then waits.");
        t->Join();
        Console::WriteLine(
            "Independent task has completed; main thread ends.");  
    }

private:
    // The callback method must match the signature of the
    // callback delegate.
    //
    static void ResultCallback(int lineCount) 
    {
        Console::WriteLine(
            "Independent task printed {0} lines.", lineCount);
    }
};

// Entry point for the example.
//
void main() 
{
    Example::Demo();
}

Voir aussi

Référence

Thread

ThreadStart

ParameterizedThreadStart

Thread.Start

Autres ressources

Threading managé

Utilisation des threads et du threading