オペレーティング システム プロセスが作成されると、元のアプリケーション ドメインを含め、そのプロセスでコードを実行するスレッドがオペレーティング システムによって挿入されます。 その時点から、オペレーティング システム スレッドが必ずしも作成または破棄されることなく、アプリケーション ドメインを作成および破棄できます。 実行中のコードがマネージド コードの場合、現在のアプリケーション ドメインで実行されているスレッドのThread オブジェクトを取得するには、CurrentThread型の静的Thread プロパティを取得します。 このトピックでは、スレッドの作成について説明し、スレッド プロシージャにデータを渡すための代替方法について説明します。
新しい Thread オブジェクトを作成すると、新しいマネージド スレッドが作成されます。
Thread クラスには、ThreadStart デリゲートまたはParameterizedThreadStart デリゲートを受け取るコンストラクターがあります。デリゲートは、Start メソッドを呼び出すときに新しいスレッドによって呼び出されるメソッドをラップします。
Startを1回以上呼び出すと、ThreadStateExceptionがスローされます。
Start メソッドは、多くの場合、新しいスレッドが実際に開始される前に、直ちに戻ります。
ThreadStateプロパティとIsAliveプロパティを使用して、いつでもスレッドの状態を判断できますが、これらのプロパティはスレッドのアクティビティの同期には使用しないでください。
注意
スレッドが開始されたら、 Thread オブジェクトへの参照を保持する必要はありません。 スレッドは、スレッド プロシージャが終了するまで引き続き実行されます。
次のコード例では、インスタンスと静的メソッドを別のオブジェクトで呼び出す 2 つの新しいスレッドを作成します。
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(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(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.
ParameterizedThreadStart デリゲートを使用すると、Thread.Start(Object)を呼び出すときに、データを含むオブジェクトをスレッドに簡単に渡すことができます。 コード例については、 ParameterizedThreadStart を参照してください。
ParameterizedThreadStart デリゲートを使用することは、Thread.Start(Object) メソッドが任意のオブジェクトを受け入れるため、データを渡すタイプ セーフな方法ではありません。 代わりに、スレッド プロシージャとデータをヘルパー クラスにカプセル化し、 ThreadStart デリゲートを使用してスレッド プロシージャを実行することもできます。 この手法の例を次に示します。
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("This report displays the number {0}.", 42);
// Create a thread to execute the task, and then
// start the thread.
Thread t = new(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.
非同期呼び出しからデータを返す場所がないため、 ThreadStart デリゲートも ParameterizedThreadStart デリゲートにも戻り値はありません。 スレッド メソッドの結果を取得するには、次のセクションに示すようにコールバック メソッドを使用します。
コールバック メソッドを使用してスレッドからデータを取得する
次の例は、スレッドからデータを取得するコールバック メソッドを示しています。 データとスレッド メソッドを含むクラスのコンストラクターは、コールバック メソッドを表すデリゲートも受け入れます。スレッド メソッドが終了する前に、コールバック デリゲートを呼び出します。
using System;
using System.Threading;
// The ThreadWithState2 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 ThreadWithState2
{
// 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 ThreadWithState2(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);
_callback?.Invoke(1);
}
}
// Delegate that defines the signature for the callback method.
public delegate void ExampleCallback(int lineCount);
// Entry point for the example.
public class Example2
{
public static void Main()
{
// Supply the state information required by the task.
ThreadWithState2 tws = new(
"This report displays the number {0}.",
42,
new ExampleCallback(ResultCallback)
);
Thread t = new(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 {lineCount} lines.");
}
}
// 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.