Creazione di thread e passaggio di dati all'avvio

Quando viene creato un processo del sistema operativo, il sistema operativo inserisce un thread per eseguire il codice in tale processo, inclusi i domini dell'applicazione originali. Da quel momento, i domini dell'applicazione possono essere creati ed eliminati definitivamente senza dover creare o eliminare definitivamente i thread del sistema operativo. Se il codice eseguito è codice gestito, si può ottenere un oggetto Thread per il thread in esecuzione nel dominio dell'applicazione corrente recuperando la proprietà statica CurrentThread di tipo Thread. Questo argomento descrive la creazione dei thread e illustra le alternative per passare i dati alla routine del thread.

Creazione di un thread

La creazione di un nuovo oggetto Thread crea un nuovo thread gestito. La classe Thread ha costruttori che accettano un delegato ThreadStart o un delegato ParameterizedThreadStart. Il delegato esegue il wrapping del metodo richiamato dal nuovo thread quando si chiama il metodo Start. Se si chiama Start più di una volta, viene generata un'eccezione ThreadStateException.

Il metodo Start restituisce il controllo immediatamente, spesso prima che il nuovo thread sia stato effettivamente avviato. È possibile usare le proprietà ThreadState e IsAlive per determinare lo stato del thread in qualsiasi momento, ma è consigliabile non usare mai queste proprietà per la sincronizzazione delle attività dei thread.

L'esempio di codice seguente crea due nuovi thread per chiamare metodi di istanza e statici su un altro oggetto.

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.");
    }
};

public ref class Simple
{
public:
    static void Main()
    {
        ServerClass^ serverObject = gcnew ServerClass();

        // Create the thread object, passing in the
        // serverObject.InstanceMethod method using a
        // ThreadStart delegate.
        Thread^ InstanceCaller = gcnew Thread(
            gcnew ThreadStart(serverObject, &ServerClass::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 = gcnew Thread(
            gcnew ThreadStart(&ServerClass::StaticMethod));

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

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

int main()
{
    Simple::Main();
}
// The example displays output like the following:
//       The Main() thread calls this after starting the new InstanceCaller thread.
//       The Main() thread calls this after starting the new StaticCaller thread.
//       ServerClass.StaticMethod is running on another thread.
//       ServerClass.InstanceMethod is running on another thread.
//       The instance method called by the worker thread has ended.
//       The static method called by the worker thread has ended.

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 void Main()
    {
        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.");
    }
}
// The example displays the output like the following:
//    The Main() thread calls this after starting the new InstanceCaller thread.
//    The Main() thread calls this after starting the new StaticCaller thread.
//    ServerClass.StaticMethod is running on another thread.
//    ServerClass.InstanceMethod is running on another thread.
//    The instance method called by the worker thread has ended.
//    The static method called by the worker thread has ended.

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

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

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

Public class Simple
    Public Shared Sub Main()
        Dim serverObject As New ServerClass()

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

        ' Start the thread.
        SharedCaller.Start()

        Console.WriteLine("The Main() thread calls this after " _
            + "starting the new SharedCaller thread.")
    End Sub
End Class
' The example displays output like the following:
'    The Main() thread calls this after starting the new InstanceCaller thread.
'    The Main() thread calls this after starting the new StaticCaller thread.
'    ServerClass.StaticMethod is running on another thread.
'    ServerClass.InstanceMethod is running on another thread.
'    The instance method called by the worker thread has ended.
'    The static method called by the worker thread has ended.

Passaggio di dati ai thread

L’ora di inizio ParameterizedThreadStart fornisce un modo semplice per passare un oggetto contenente dati a un thread quando si chiama Thread.Start(Object). Per un esempio di codice, vedere ParameterizedThreadStart.

L'uso del delegato ParameterizedThreadStart non è un modo indipendente dai tipi per passare i dati, perché il metodo Thread.Start(Object) accetta qualsiasi oggetto. In alternativa è possibile incapsulare la routine del thread e i dati in una classe helper e usare il delegato ThreadStart per eseguire la routine del thread. L'esempio che segue illustra questa tecnica:

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 numberValue;

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

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

// Entry point for the example.
//
public ref class Example
{
public:
    static 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.");
    }
};

int main()
{
    Example::Main();
}
// This example displays the following output:
//       Main thread does some work, then waits.
//       This report displays the number 42.
//       Independent task has completed; main thread ends.

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 numberValue;

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

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

// 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.");
    }
}
// The example displays the following output:
//       Main thread does some work, then waits.
//       This report displays the number 42.
//       Independent task has completed; main thread ends.

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 numberValue As Integer

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

    ' The thread procedure performs the task, such as formatting
    ' and printing a document.
    Public Sub ThreadProc()
        Console.WriteLine(boilerplate, numberValue)
    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(New ThreadStart(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
' The example displays the following output:
'       Main thread does some work, then waits.
'       This report displays the number 42.
'       Independent task has completed; main thread ends.

Nessuno dei due delegati, ThreadStart e ParameterizedThreadStart, ha un valore restituito, perché non è possibile restituire i dati da una chiamata asincrona. Per recuperare i risultati di un metodo di thread, è possibile usare un metodo di callback, come illustrato nella sezione successiva.

Recupero dei dati dai thread con i metodi di callback

L'esempio seguente illustra un metodo di callback che recupera i dati da un thread. Il costruttore della classe che contiene i dati e il metodo del thread accetta anche un delegato che rappresenta il metodo di callback. Prima che il metodo del thread termini, richiama il delegato di callback.

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 numberValue;

    // 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;
        numberValue = 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, numberValue);
        if (callback != nullptr)
        {
            callback(1);
        }
    }
};

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

        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.");
    }

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

int main()
{
    Example::Main();
}
// The example displays the following output:
//       Main thread does some work, then waits.
//       This report displays the number 42.
//       Independent task printed 1 lines.
//       Independent task has completed; main thread ends.

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 numberValue;

    // 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;
        numberValue = 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, numberValue);
        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);
    }
}
// The example displays the following output:
//       Main thread does some work, then waits.
//       This report displays the number 42.
//       Independent task printed 1 lines.
//       Independent task has completed; main thread ends.

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 numberValue 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(text As String, number As Integer, _
        callbackDelegate As ExampleCallback)
        boilerplate = text
        numberValue = 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, numberValue)
        If Not (callback Is Nothing) Then
            callback(1)
        End If
    End Sub
End Class

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

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, _
            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

    Public Shared Sub ResultCallback(lineCount As Integer)
        Console.WriteLine( _
            "Independent task printed {0} lines.", lineCount)
    End Sub
End Class
' The example displays the following output:
'       Main thread does some work, then waits.
'       This report displays the number 42.
'       Independent task printed 1 lines.
'       Independent task has completed; main thread ends.

Vedi anche

• Thread
• ThreadStart
• ParameterizedThreadStart
• Thread.Start
• Threading
• Utilizzo di thread e threading