Vytváření vláken a předávání dat při spuštění
Když se vytvoří proces operačního systému, operační systém vloží vlákno ke spuštění kódu v daném procesu, včetně jakékoli původní domény aplikace. Od tohoto okamžiku je možné vytvořit a zničit domény aplikace bez nutnosti vytvářet nebo zničit vlákna operačního systému. Pokud je spuštěný kód spravovaný kód, Thread lze získat objekt pro vlákno spuštěné v aktuální doméně aplikace načtením statické CurrentThread vlastnosti typu Thread. Toto téma popisuje vytvoření vlákna a popisuje alternativy pro předávání dat do procedury vlákna.
Vytvoření vlákna
Vytvoření nového Thread objektu vytvoří nové spravované vlákno. Třída Thread má konstruktory, které přebírají ThreadStart delegáta nebo ParameterizedThreadStart delegáta; delegát zabalí metodu, která je vyvolána novým vláknem při volání Start metody. Volání Start více než jednou způsobí ThreadStateException vyvolání.
Metoda Start se vrátí okamžitě, často předtím, než se nové vlákno skutečně spustilo. Pomocí vlastností IsAlive můžete ThreadState určit stav vlákna v libovolném okamžiku, ale tyto vlastnosti by se nikdy neměly používat pro synchronizaci aktivit vláken.
Poznámka:
Po spuštění vlákna není nutné zachovat odkaz na Thread objekt. Vlákno bude pokračovat v provádění až do konce procedury vlákna.
Následující příklad kódu vytvoří dvě nová vlákna pro volání instance a statických metod v jiném objektu.
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.
Předávání dat do vláken
Delegát ParameterizedThreadStart poskytuje snadný způsob, jak předat objekt obsahující data do vlákna při volání Thread.Start(Object). Podívejte se ParameterizedThreadStart na příklad kódu.
Použití delegáta ParameterizedThreadStart není typově bezpečný způsob předávání dat, protože Thread.Start(Object) metoda přijímá jakýkoli objekt. Alternativou je zapouzdření procedury vlákna a dat v pomocné třídě a použití delegáta ThreadStart ke spuštění procedury vlákna. Následující příklad ukazuje tuto techniku:
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.
ParameterizedThreadStart Ani ThreadStart delegát nemá návratovou hodnotu, protože neexistuje žádné místo pro vrácení dat z asynchronního volání. Pokud chcete načíst výsledky metody vlákna, můžete použít metodu zpětného volání, jak je znázorněno v další části.
Načítání dat z vláken pomocí metod zpětného volání
Následující příklad ukazuje metodu zpětného volání, která načítá data z vlákna. Konstruktor pro třídu, která obsahuje data a vlákno metoda také přijímá delegát představující metodu zpětného volání; před ukončením metody vlákna vyvolá delegát zpětného volání.
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.
Viz také
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