Creación de subprocesos y análisis los datos en el inicio

Cuando se crea un proceso de sistema operativo, el sistema operativo inserta un subproceso para ejecutar el código en dicho proceso, incluido cualquier dominio de aplicación original. Desde ese momento, los dominios de aplicación se pueden crear y destruir sin que se cree o destruya necesariamente ningún subproceso del sistema operativo. Si el código ejecutado es código administrado, se puede obtener un objeto Thread para el subproceso que se ejecuta en el dominio de aplicación actual mediante la recuperación de la propiedad CurrentThread estática de tipo Thread. En este tema se describe la creación de subprocesos y se analizan las alternativas para pasar datos al procedimiento de los subprocesos.

Creación de un subproceso

Al crear un objeto Thread, se crea un subproceso administrado. La clase Thread tiene constructores que adoptan un delegado ThreadStart o un delegado ParameterizedThreadStart; el delegado ajusta el método invocado por el nuevo subproceso cuando llama al método Start. Al llamar a Start más de una vez, se inicia ThreadStateException.

El método Start se devuelve inmediatamente, a menudo antes de que se haya iniciado realmente el nuevo subproceso. Puede usar las propiedades ThreadState y IsAlive para determinar el estado del subproceso en cualquier momento, pero estas propiedades nunca deben utilizarse para sincronizar las actividades de los subprocesos.

Nota

Una vez que se inicia un subproceso, no es necesario conservar una referencia al objeto Thread. El subproceso continúa ejecutándose hasta que finaliza el procedimiento del subproceso.

En el ejemplo de código siguiente se crean dos subprocesos para llamar a métodos estáticos e instancias en otro objeto.

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.

Paso de datos a subprocesos

El delegado ParameterizedThreadStart ofrece una forma sencilla de pasar un objeto que contiene datos a un subproceso al llamar a Thread.Start(Object). Vea ParameterizedThreadStart para obtener código muestra.

El uso del delegado ParameterizedThreadStart no es una forma con seguridad de tipos de pasar datos, porque el método Thread.Start(Object) acepta cualquier objeto. Una alternativa consiste en encapsular el procedimiento de subprocesos y los datos en una clase del asistente y utilizar el delegado ThreadStart para ejecutar el procedimiento de subprocesos. En el siguiente ejemplo se muestra esta técnica:

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.

Ninguno de estos delegados, ThreadStart ni ParameterizedThreadStart, tiene un valor devuelto, porque no hay ningún lugar para devolver los datos de una llamada asincrónica. Para recuperar los resultados de un método de subproceso, puede utilizar un método de devolución de llamada, como se muestra en la siguiente sección.

Recuperación de datos de subprocesos con métodos de devolución de llamada

En el ejemplo siguiente se muestra un método de devolución de llamada que recupera datos de un subproceso. El constructor de la clase que contiene los datos y el método del subproceso también acepta a un delegado que representa el método de devolución de llamada; antes de que finalice el método del subproceso, invoca al delegado de devolución de llamada.

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.

Vea también