Interlocked.CompareExchange Interlocked.CompareExchange Interlocked.CompareExchange Interlocked.CompareExchange Method

定義

2 つの値が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two values for equality and, if they are equal, replaces the first value.

オーバーロード

CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double)

2 つの倍精度浮動小数点数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two double-precision floating point numbers for equality and, if they are equal, replaces the first value.

CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32)

2 つの 32 ビット符号付き整数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two 32-bit signed integers for equality and, if they are equal, replaces the first value.

CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64)

2 つの 64 ビット符号付き整数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two 64-bit signed integers for equality and, if they are equal, replaces the first value.

CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr)

2 つのプラットフォーム固有のハンドルまたはポインターが等しいかどうかを比較します。等しい場合は、最初の 1 つを置き換えます。Compares two platform-specific handles or pointers for equality and, if they are equal, replaces the first one.

CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object)

2 つのオブジェクトの参照が等値であるかどうかを比較します。等しい場合は、最初のオブジェクトを置き換えます。Compares two objects for reference equality and, if they are equal, replaces the first object.

CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single)

2 つの単精度浮動小数点数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two single-precision floating point numbers for equality and, if they are equal, replaces the first value.

CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T)

指定した参照型 T の 2 つのインスタンスの参照が等しいかどうかを比較します。等しい場合は、最初の 1 つを置き換えます。Compares two instances of the specified reference type T for reference equality and, if they are equal, replaces the first one.

CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double) CompareExchange(Double, Double, Double)

2 つの倍精度浮動小数点数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two double-precision floating point numbers for equality and, if they are equal, replaces the first value.

public:
 static double CompareExchange(double % location1, double value, double comparand);
public static double CompareExchange (ref double location1, double value, double comparand);
static member CompareExchange : double * double * double -> double
Public Shared Function CompareExchange (ByRef location1 As Double, value As Double, comparand As Double) As Double

パラメーター

location1
Double Double Double Double

値を comparand と比較し、場合によっては置き換える比較先。The destination, whose value is compared with comparand and possibly replaced.

value
Double Double Double Double

比較した結果が等しい場合に比較先の値を置き換える値。The value that replaces the destination value if the comparison results in equality.

comparand
Double Double Double Double

location1 にある値と比較する値。The value that is compared to the value at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

次のコード例は、実行中のDouble合計値を累積するスレッドセーフなメソッドを示しています。The following code example demonstrates a thread-safe method that accumulates a running total of Double values. 2つのスレッドは、 Doubleスレッドセーフなメソッドと通常の加算を使用して一連の値を追加し、スレッドが完了すると合計が比較されます。Two threads add a series of Double values using the thread-safe method and ordinary addition, and when the threads complete the totals are compared. デュアルプロセッサコンピューターでは、合計に大きな違いがあります。On a dual-processor computer, there is a significant difference in the totals.

スレッドセーフなメソッドでは、実行中の合計の初期値が保存されます。 CompareExchangeその後、メソッドを使用して、新しく計算された合計を古い合計と交換します。In the thread-safe method, the initial value of the running total is saved, and then the CompareExchange method is used to exchange the newly computed total with the old total. 戻り値が、実行中の合計の保存値と等しくない場合は、その間に別のスレッドによって合計が更新されます。If the return value is not equal to the saved value of the running total, then another thread has updated the total in the meantime. その場合は、実行中の合計を更新しようとする必要があります。In that case, the attempt to update the running total must be repeated.

// This example demonstrates a thread-safe method that adds to a
// running total.  
using System;
using System.Threading;

public class ThreadSafe
{
    // Field totalValue contains a running total that can be updated
    // by multiple threads. It must be protected from unsynchronized 
    // access.
    private double totalValue = 0.0;

    // The Total property returns the running total.
    public double Total { get { return totalValue; }}

    // AddToTotal safely adds a value to the running total.
    public double AddToTotal(double addend)
    {
        double initialValue, computedValue;
        do
        {
            // Save the current running total in a local variable.
            initialValue = totalValue;

            // Add the new value to the running total.
            computedValue = initialValue + addend;

            // CompareExchange compares totalValue to initialValue. If
            // they are not equal, then another thread has updated the
            // running total since this loop started. CompareExchange
            // does not update totalValue. CompareExchange returns the
            // contents of totalValue, which do not equal initialValue,
            // so the loop executes again.
        }
        while (initialValue != Interlocked.CompareExchange(ref totalValue, 
            computedValue, initialValue));
        // If no other thread updated the running total, then 
        // totalValue and initialValue are equal when CompareExchange
        // compares them, and computedValue is stored in totalValue.
        // CompareExchange returns the value that was in totalValue
        // before the update, which is equal to initialValue, so the 
        // loop ends.

        // The function returns computedValue, not totalValue, because
        // totalValue could be changed by another thread between
        // the time the loop ends and the function returns.
        return computedValue;
    }
}

public class Test
{
    // Create an instance of the ThreadSafe class to test.
    private static ThreadSafe ts = new ThreadSafe();
    private static double control;

    private static Random r = new Random();
    private static ManualResetEvent mre = new ManualResetEvent(false);

    public static void Main()
    {
        // Create two threads, name them, and start them. The
        // thread will block on mre.
        Thread t1 = new Thread(TestThread);
        t1.Name = "Thread 1";
        t1.Start();
        Thread t2 = new Thread(TestThread);
        t2.Name = "Thread 2";
        t2.Start();

        // Now let the threads begin adding random numbers to 
        // the total.
        mre.Set();
        
        // Wait until all the threads are done.
        t1.Join();
        t2.Join();

        Console.WriteLine("Thread safe: {0}  Ordinary Double: {1}", 
            ts.Total, control);
    }

    private static void TestThread()
    {
        // Wait until the signal.
        mre.WaitOne();

        for(int i = 1; i <= 1000000; i++)
        {
            // Add to the running total in the ThreadSafe instance, and
            // to an ordinary double.
            //
            double testValue = r.NextDouble();
            control += testValue;
            ts.AddToTotal(testValue);
        }
    }
}

/* On a dual-processor computer, this code example produces output 
   similar to the following:

Thread safe: 998068.049623744  Ordinary Double: 759775.417190589
 */
' This example demonstrates a thread-safe method that adds to a
' running total.  
Imports System.Threading

Public Class ThreadSafe
    ' Field totalValue contains a running total that can be updated
    ' by multiple threads. It must be protected from unsynchronized 
    ' access.
    Private totalValue As Double = 0.0

    ' The Total property returns the running total.
    Public ReadOnly Property Total As Double
        Get
            Return totalValue
        End Get
    End Property

    ' AddToTotal safely adds a value to the running total.
    Public Function AddToTotal(ByVal addend As Double) As Double
        Dim initialValue, computedValue As Double
        Do
            ' Save the current running total in a local variable.
            initialValue = totalValue

            ' Add the new value to the running total.
            computedValue = initialValue + addend

            ' CompareExchange compares totalValue to initialValue. If
            ' they are not equal, then another thread has updated the
            ' running total since this loop started. CompareExchange
            ' does not update totalValue. CompareExchange returns the
            ' contents of totalValue, which do not equal initialValue,
            ' so the loop executes again.
        Loop While initialValue <> Interlocked.CompareExchange( _
            totalValue, computedValue, initialValue)
        ' If no other thread updated the running total, then 
        ' totalValue and initialValue are equal when CompareExchange
        ' compares them, and computedValue is stored in totalValue.
        ' CompareExchange returns the value that was in totalValue
        ' before the update, which is equal to initialValue, so the 
        ' loop ends.

        ' The function returns computedValue, not totalValue, because
        ' totalValue could be changed by another thread between
        ' the time the loop ends and the function returns.
        Return computedValue
    End Function
End Class

Public Class Test
    ' Create an instance of the ThreadSafe class to test.
    Private Shared ts As New ThreadSafe()
    Private Shared control As Double

    Private Shared r As New Random()
    Private Shared mre As New ManualResetEvent(false)

    <MTAThread> _
    Public Shared Sub Main()
        ' Create two threads, name them, and start them. The
        ' threads will block on mre.
        Dim t1 As New Thread(AddressOf TestThread)
        t1.Name = "Thread 1"
        t1.Start()
        Dim t2 As New Thread(AddressOf TestThread)
        t2.Name = "Thread 2"
        t2.Start()

        ' Now let the threads begin adding random numbers to 
        ' the total.
        mre.Set()
        
        ' Wait until all the threads are done.
        t1.Join()
        t2.Join()

        Console.WriteLine("Thread safe: {0}  Ordinary Double: {1}", ts.Total, control)
    End Sub

    Private Shared Sub TestThread()
        ' Wait until the signal.
        mre.WaitOne()

        For i As Integer = 1 to 1000000
            ' Add to the running total in the ThreadSafe instance, and
            ' to an ordinary double.
            '
            Dim testValue As Double = r.NextDouble
            control += testValue
            ts.AddToTotal(testValue)
        Next
    End Sub
End Class

' On a dual-processor computer, this code example produces output 
' similar to the following:
'
'Thread safe: 998068.049623744  Ordinary Double: 759775.417190589

注釈

comparandlocation1値が等しい場合、 valueはにlocation1格納されます。If comparand and the value in location1 are equal, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. の戻り値はCompareExchange 、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

こちらもご覧ください

CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32) CompareExchange(Int32, Int32, Int32)

2 つの 32 ビット符号付き整数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two 32-bit signed integers for equality and, if they are equal, replaces the first value.

public:
 static int CompareExchange(int % location1, int value, int comparand);
public static int CompareExchange (ref int location1, int value, int comparand);
static member CompareExchange : int * int * int -> int
Public Shared Function CompareExchange (ByRef location1 As Integer, value As Integer, comparand As Integer) As Integer

パラメーター

location1
Int32 Int32 Int32 Int32

値を comparand と比較し、場合によっては置き換える比較先。The destination, whose value is compared with comparand and possibly replaced.

value
Int32 Int32 Int32 Int32

比較した結果が等しい場合に比較先の値を置き換える値。The value that replaces the destination value if the comparison results in equality.

comparand
Int32 Int32 Int32 Int32

location1 にある値と比較する値。The value that is compared to the value at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

次のコード例は、実行中の合計を累積したスレッドセーフなメソッドを示しています。The following code example demonstrates a thread-safe method that accumulates a running total. 実行中の合計の初期値が保存されます。 CompareExchangeその後、メソッドを使用して、新しく計算された合計を古い合計と交換します。The initial value of the running total is saved, and then the CompareExchange method is used to exchange the newly computed total with the old total. 戻り値が、実行中の合計の保存値と等しくない場合は、その間に別のスレッドによって合計が更新されます。If the return value is not equal to the saved value of the running total, then another thread has updated the total in the meantime. その場合は、実行中の合計を更新しようとする必要があります。In that case, the attempt to update the running total must be repeated.

注意

.NET Framework Addのバージョン2.0 で導入されたメソッドは、整数のスレッドセーフな実行合計を累積するためのより便利な方法を提供します。The Add method, introduced in version 2.0 of the .NET Framework, provides a more convenient way to accumulate thread-safe running totals for integers.

// This example demonstrates a thread-safe method that adds to a
// running total.  It cannot be run directly.  You can compile it
// as a library, or add the class to a project.
#using <system.dll>

using namespace System::Threading;
public ref class ThreadSafe
{
private:

   // totalValue contains a running total that can be updated
   // by multiple threads. It must be protected from unsynchronized 
   // access.
   int totalValue;

public:

   property int Total 
   {

      // The Total property returns the running total.
      int get()
      {
         return totalValue;
      }

   }

   // AddToTotal safely adds a value to the running total.
   int AddToTotal( int addend )
   {
      int initialValue;
      int computedValue;
      do
      {
         
         // Save the current running total in a local variable.
         initialValue = totalValue;
         
         // Add the new value to the running total.
         computedValue = initialValue + addend;
         
         // CompareExchange compares totalValue to initialValue. If
         // they are not equal, then another thread has updated the
         // running total since this loop started. CompareExchange
         // does not update totalValue. CompareExchange returns the
         // contents of totalValue, which do not equal initialValue,
         // so the loop executes again.
      }
      while ( initialValue != Interlocked::CompareExchange( totalValue, computedValue, initialValue ) );

      
      // If no other thread updated the running total, then 
      // totalValue and initialValue are equal when CompareExchange
      // compares them, and computedValue is stored in totalValue.
      // CompareExchange returns the value that was in totalValue
      // before the update, which is equal to initialValue, so the 
      // loop ends.
      // The function returns computedValue, not totalValue, because
      // totalValue could be changed by another thread between
      // the time the loop ends and the function returns.
      return computedValue;
   }

};

// This example demonstrates a thread-safe method that adds to a
// running total.  It cannot be run directly.  You can compile it
// as a library, or add the class to a project.
using System.Threading;

public class ThreadSafe {
    // totalValue contains a running total that can be updated
    // by multiple threads. It must be protected from unsynchronized 
    // access.
    private int totalValue = 0;

    // The Total property returns the running total.
    public int Total {
        get { return totalValue; }
    }

    // AddToTotal safely adds a value to the running total.
    public int AddToTotal(int addend) {
        int initialValue, computedValue;
        do {
            // Save the current running total in a local variable.
            initialValue = totalValue;

            // Add the new value to the running total.
            computedValue = initialValue + addend;

            // CompareExchange compares totalValue to initialValue. If
            // they are not equal, then another thread has updated the
            // running total since this loop started. CompareExchange
            // does not update totalValue. CompareExchange returns the
            // contents of totalValue, which do not equal initialValue,
            // so the loop executes again.
        } while (initialValue != Interlocked.CompareExchange(
            ref totalValue, computedValue, initialValue));
        // If no other thread updated the running total, then 
        // totalValue and initialValue are equal when CompareExchange
        // compares them, and computedValue is stored in totalValue.
        // CompareExchange returns the value that was in totalValue
        // before the update, which is equal to initialValue, so the 
        // loop ends.

        // The function returns computedValue, not totalValue, because
        // totalValue could be changed by another thread between
        // the time the loop ends and the function returns.
        return computedValue;
    }
}
' This example demonstrates a thread-safe method that adds to a
' running total.  It cannot be run directly.  You can compile it
' as a library, or add the class to a project.
Imports System.Threading

Public Class ThreadSafe
    ' Field totalValue contains a running total that can be updated
    ' by multiple threads. It must be protected from unsynchronized 
    ' access.
    Private totalValue As Integer = 0

    ' The Total property returns the running total.
    Public ReadOnly Property Total As Integer
        Get
            Return totalValue
        End Get
    End Property

    ' AddToTotal safely adds a value to the running total.
    Public Function AddToTotal(ByVal addend As Integer) As Integer
        Dim initialValue, computedValue As Integer
        Do
            ' Save the current running total in a local variable.
            initialValue = totalValue

            ' Add the new value to the running total.
            computedValue = initialValue + addend

            ' CompareExchange compares totalValue to initialValue. If
            ' they are not equal, then another thread has updated the
            ' running total since this loop started. CompareExchange
            ' does not update totalValue. CompareExchange returns the
            ' contents of totalValue, which do not equal initialValue,
            ' so the loop executes again.
        Loop While initialValue <> Interlocked.CompareExchange( _
            totalValue, computedValue, initialValue)
        ' If no other thread updated the running total, then 
        ' totalValue and initialValue are equal when CompareExchange
        ' compares them, and computedValue is stored in totalValue.
        ' CompareExchange returns the value that was in totalValue
        ' before the update, which is equal to initialValue, so the 
        ' loop ends.

        ' The function returns computedValue, not totalValue, because
        ' totalValue could be changed by another thread between
        ' the time the loop ends and the function returns.
        Return computedValue
    End Function
End Class

注釈

comparandlocation1値が等しい場合、 valueはにlocation1格納されます。If comparand and the value in location1 are equal, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. の戻り値はCompareExchange 、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

こちらもご覧ください

CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64) CompareExchange(Int64, Int64, Int64)

2 つの 64 ビット符号付き整数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two 64-bit signed integers for equality and, if they are equal, replaces the first value.

public:
 static long CompareExchange(long % location1, long value, long comparand);
public static long CompareExchange (ref long location1, long value, long comparand);
static member CompareExchange : int64 * int64 * int64 -> int64
Public Shared Function CompareExchange (ByRef location1 As Long, value As Long, comparand As Long) As Long

パラメーター

location1
Int64 Int64 Int64 Int64

値を comparand と比較し、場合によっては置き換える比較先。The destination, whose value is compared with comparand and possibly replaced.

value
Int64 Int64 Int64 Int64

比較した結果が等しい場合に比較先の値を置き換える値。The value that replaces the destination value if the comparison results in equality.

comparand
Int64 Int64 Int64 Int64

location1 にある値と比較する値。The value that is compared to the value at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

注釈

comparandlocation1値が等しい場合、 valueはにlocation1格納されます。If comparand and the value in location1 are equal, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. の戻り値はCompareExchange 、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

こちらもご覧ください

CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr) CompareExchange(IntPtr, IntPtr, IntPtr)

2 つのプラットフォーム固有のハンドルまたはポインターが等しいかどうかを比較します。等しい場合は、最初の 1 つを置き換えます。Compares two platform-specific handles or pointers for equality and, if they are equal, replaces the first one.

public:
 static IntPtr CompareExchange(IntPtr % location1, IntPtr value, IntPtr comparand);
public static IntPtr CompareExchange (ref IntPtr location1, IntPtr value, IntPtr comparand);
static member CompareExchange : nativeint * nativeint * nativeint -> nativeint
Public Shared Function CompareExchange (ByRef location1 As IntPtr, value As IntPtr, comparand As IntPtr) As IntPtr

パラメーター

location1
IntPtr IntPtr IntPtr IntPtr

値を comparand の値と比較し、場合によっては value によって置き換える、比較先の IntPtrThe destination IntPtr, whose value is compared with the value of comparand and possibly replaced by value.

value
IntPtr IntPtr IntPtr IntPtr

比較した結果が等しい場合に比較先の値を置き換える IntPtrThe IntPtr that replaces the destination value if the comparison results in equality.

comparand
IntPtr IntPtr IntPtr IntPtr

location1 にある値と比較する IntPtrThe IntPtr that is compared to the value at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

注釈

comparandlocation1値が等しい場合、 valueはにlocation1格納されます。If comparand and the value in location1 are equal, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. このメソッドの戻り値は、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of this method is the original value in location1, whether or not the exchange takes place.

注意

IntPtrはプラットフォーム固有の型です。IntPtr is a platform-specific type.

こちらもご覧ください

CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object) CompareExchange(Object, Object, Object)

2 つのオブジェクトの参照が等値であるかどうかを比較します。等しい場合は、最初のオブジェクトを置き換えます。Compares two objects for reference equality and, if they are equal, replaces the first object.

public:
 static System::Object ^ CompareExchange(System::Object ^ % location1, System::Object ^ value, System::Object ^ comparand);
public static object CompareExchange (ref object location1, object value, object comparand);
static member CompareExchange : obj * obj * obj -> obj
Public Shared Function CompareExchange (ByRef location1 As Object, value As Object, comparand As Object) As Object

パラメーター

location1
Object Object Object Object

参照によって comparand と比較し、場合によっては置き換える比較先のオブジェクト。The destination object that is compared by reference with comparand and possibly replaced.

value
Object Object Object Object

参照の比較の結果が等しい場合に比較先のオブジェクトを置き換えるオブジェクト。The object that replaces the destination object if the reference comparison results in equality.

comparand
Object Object Object Object

location1 にあるオブジェクトと、参照によって比較されるオブジェクト。The object that is compared by reference to the object at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

注釈

重要

.NET Framework 2.0 より、CompareExchange<T>(T, T, T) メソッド オーバーロードから参照型に対してタイプ セーフの代替が提供されます。Beginning with .NET Framework 2.0, the CompareExchange<T>(T, T, T) method overload provides a type-safe alternative for reference types. このオーバーロードの代わりに呼び出すことをお勧めします。We recommend that you call it instead of this overload.

comparandlocation1オブジェクトが参照によってvalue等しい場合、はにlocation1格納されます。If comparand and the object in location1 are equal by reference, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. の戻り値はCompareExchange 、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

注意

オブジェクトは、値の等価性ではなく、参照の等価性が比較されます。The objects are compared for reference equality rather than value equality. その結果、同じ値の型の2つのボックス化されたインスタンス (たとえば、整数 3) は常に等しくないように見え、操作は実行されません。As a result, two boxed instances of the same value type (for example, the integer 3) always appear to be unequal and no operation is performed. 値型では、このオーバーロードを使用しないでください。Do not use this overload with value types.

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CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single) CompareExchange(Single, Single, Single)

2 つの単精度浮動小数点数が等しいかどうかを比較します。等しい場合は、最初の値を置き換えます。Compares two single-precision floating point numbers for equality and, if they are equal, replaces the first value.

public:
 static float CompareExchange(float % location1, float value, float comparand);
public static float CompareExchange (ref float location1, float value, float comparand);
static member CompareExchange : single * single * single -> single
Public Shared Function CompareExchange (ByRef location1 As Single, value As Single, comparand As Single) As Single

パラメーター

location1
Single Single Single Single

値を comparand と比較し、場合によっては置き換える比較先。The destination, whose value is compared with comparand and possibly replaced.

value
Single Single Single Single

比較した結果が等しい場合に比較先の値を置き換える値。The value that replaces the destination value if the comparison results in equality.

comparand
Single Single Single Single

location1 にある値と比較する値。The value that is compared to the value at location1.

戻り値

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

次のコード例は、実行中のSingle合計値を累積するスレッドセーフなメソッドを示しています。The following code example demonstrates a thread-safe method that accumulates a running total of Single values. 2つのスレッドは、 Singleスレッドセーフなメソッドと通常の加算を使用して一連の値を追加し、スレッドが完了すると合計が比較されます。Two threads add a series of Single values using the thread-safe method and ordinary addition, and when the threads complete the totals are compared. デュアルプロセッサコンピューターでは、合計に大きな違いがあります。On a dual-processor computer, there is a significant difference in the totals.

スレッドセーフなメソッドでは、実行中の合計の初期値が保存されます。 CompareExchangeその後、メソッドを使用して、新しく計算された合計を古い合計と交換します。In the thread-safe method, the initial value of the running total is saved, and then the CompareExchange method is used to exchange the newly computed total with the old total. 戻り値が、実行中の合計の保存値と等しくない場合は、その間に別のスレッドによって合計が更新されます。If the return value is not equal to the saved value of the running total, then another thread has updated the total in the meantime. その場合は、実行中の合計を更新しようとする必要があります。In that case, the attempt to update the running total must be repeated.

// This example demonstrates a thread-safe method that adds to a
// running total.  
using System;
using System.Threading;

public class ThreadSafe
{
    // Field totalValue contains a running total that can be updated
    // by multiple threads. It must be protected from unsynchronized 
    // access.
    private float totalValue = 0.0F;

    // The Total property returns the running total.
    public float Total { get { return totalValue; }}

    // AddToTotal safely adds a value to the running total.
    public float AddToTotal(float addend)
    {
        float initialValue, computedValue;
        do
        {
            // Save the current running total in a local variable.
            initialValue = totalValue;

            // Add the new value to the running total.
            computedValue = initialValue + addend;

            // CompareExchange compares totalValue to initialValue. If
            // they are not equal, then another thread has updated the
            // running total since this loop started. CompareExchange
            // does not update totalValue. CompareExchange returns the
            // contents of totalValue, which do not equal initialValue,
            // so the loop executes again.
        }
        while (initialValue != Interlocked.CompareExchange(ref totalValue, 
            computedValue, initialValue));
        // If no other thread updated the running total, then 
        // totalValue and initialValue are equal when CompareExchange
        // compares them, and computedValue is stored in totalValue.
        // CompareExchange returns the value that was in totalValue
        // before the update, which is equal to initialValue, so the 
        // loop ends.

        // The function returns computedValue, not totalValue, because
        // totalValue could be changed by another thread between
        // the time the loop ends and the function returns.
        return computedValue;
    }
}

public class Test
{
    // Create an instance of the ThreadSafe class to test.
    private static ThreadSafe ts = new ThreadSafe();
    private static float control;

    private static Random r = new Random();
    private static ManualResetEvent mre = new ManualResetEvent(false);

    public static void Main()
    {
        // Create two threads, name them, and start them. The
        // thread will block on mre.
        Thread t1 = new Thread(TestThread);
        t1.Name = "Thread 1";
        t1.Start();
        Thread t2 = new Thread(TestThread);
        t2.Name = "Thread 2";
        t2.Start();

        // Now let the threads begin adding random numbers to 
        // the total.
        mre.Set();
        
        // Wait until all the threads are done.
        t1.Join();
        t2.Join();

        Console.WriteLine("Thread safe: {0}  Ordinary float: {1}", 
            ts.Total, control);
    }

    private static void TestThread()
    {
        // Wait until the signal.
        mre.WaitOne();

        for(int i = 1; i <= 1000000; i++)
        {
            // Add to the running total in the ThreadSafe instance, and
            // to an ordinary float.
            //
            float testValue = (float) r.NextDouble();
            control += testValue;
            ts.AddToTotal(testValue);
        }
    }
}

/* On a dual-processor computer, this code example produces output 
   similar to the following:

Thread safe: 17039.57  Ordinary float: 15706.44
 */
' This example demonstrates a thread-safe method that adds to a
' running total.  
Imports System.Threading

Public Class ThreadSafe
    ' Field totalValue contains a running total that can be updated
    ' by multiple threads. It must be protected from unsynchronized 
    ' access.
    Private totalValue As Single = 0.0

    ' The Total property returns the running total.
    Public ReadOnly Property Total As Single
        Get
            Return totalValue
        End Get
    End Property

    ' AddToTotal safely adds a value to the running total.
    Public Function AddToTotal(ByVal addend As Single) As Single
        Dim initialValue, computedValue As Single
        Do
            ' Save the current running total in a local variable.
            initialValue = totalValue

            ' Add the new value to the running total.
            computedValue = initialValue + addend

            ' CompareExchange compares totalValue to initialValue. If
            ' they are not equal, then another thread has updated the
            ' running total since this loop started. CompareExchange
            ' does not update totalValue. CompareExchange returns the
            ' contents of totalValue, which do not equal initialValue,
            ' so the loop executes again.
        Loop While initialValue <> Interlocked.CompareExchange( _
            totalValue, computedValue, initialValue)
        ' If no other thread updated the running total, then 
        ' totalValue and initialValue are equal when CompareExchange
        ' compares them, and computedValue is stored in totalValue.
        ' CompareExchange returns the value that was in totalValue
        ' before the update, which is equal to initialValue, so the 
        ' loop ends.

        ' The function returns computedValue, not totalValue, because
        ' totalValue could be changed by another thread between
        ' the time the loop ends and the function returns.
        Return computedValue
    End Function
End Class

Public Class Test
    ' Create an instance of the ThreadSafe class to test.
    Private Shared ts As New ThreadSafe()
    Private Shared control As Single

    Private Shared r As New Random()
    Private Shared mre As New ManualResetEvent(false)

    <MTAThread> _
    Public Shared Sub Main()
        ' Create two threads, name them, and start them. The
        ' threads will block on mre.
        Dim t1 As New Thread(AddressOf TestThread)
        t1.Name = "Thread 1"
        t1.Start()
        Dim t2 As New Thread(AddressOf TestThread)
        t2.Name = "Thread 2"
        t2.Start()

        ' Now let the threads begin adding random numbers to 
        ' the total.
        mre.Set()
        
        ' Wait until all the threads are done.
        t1.Join()
        t2.Join()

        Console.WriteLine("Thread safe: {0}  Ordinary Single: {1}", ts.Total, control)
    End Sub

    Private Shared Sub TestThread()
        ' Wait until the signal.
        mre.WaitOne()

        For i As Integer = 1 to 1000000
            ' Add to the running total in the ThreadSafe instance, and
            ' to an ordinary Single.
            '
            Dim testValue As Single = r.NextDouble()
            control += testValue
            ts.AddToTotal(testValue)
        Next
    End Sub
End Class

' On a dual-processor computer, this code example produces output 
' similar to the following:
'
'Thread safe: 17039.57  Ordinary Single: 15706.44

注釈

comparandlocation1値が等しい場合、 valueはにlocation1格納されます。If comparand and the value in location1 are equal, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較操作と交換操作は、分割不可能な操作として実行されます。The compare and exchange operations are performed as an atomic operation. の戻り値はCompareExchange 、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

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CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T) CompareExchange<T>(T, T, T)

指定した参照型 T の 2 つのインスタンスの参照が等しいかどうかを比較します。等しい場合は、最初の 1 つを置き換えます。Compares two instances of the specified reference type T for reference equality and, if they are equal, replaces the first one.

public:
generic <typename T>
 where T : class static T CompareExchange(T % location1, T value, T comparand);
[System.Runtime.InteropServices.ComVisible(false)]
public static T CompareExchange<T> (ref T location1, T value, T comparand) where T : class;
static member CompareExchange : 'T * 'T * 'T -> 'T (requires 'T : null)
Public Shared Function CompareExchange(Of T As Class) (ByRef location1 As T, value As T, comparand As T) As T

型パラメーター

T

location1value、および comparand に使用する型。The type to be used for location1, value, and comparand. この型は、参照型である必要があります。This type must be a reference type.

パラメーター

location1
T T T T

参照によって値を comparand と比較し、場合によっては置き換える比較先。The destination, whose value is compared by reference with comparand and possibly replaced. これは参照パラメーターです (C# では ref、Visual Basic では ByRef)。This is a reference parameter (ref in C#, ByRef in Visual Basic).

value
T T T T

参照によって比較した結果が等しい場合に比較先の値を置き換える値。The value that replaces the destination value if the comparison by reference results in equality.

comparand
T T T T

location1 にある値と参照によって比較される値。The value that is compared by reference to the value at location1.

戻り値

T T T T

location1 の元の値。The original value in location1.

例外

location1 のアドレスは null ポインターです。The address of location1 is a null pointer.

注釈

comparandlocation1値が参照によってvalue等しい場合、はにlocation1格納されます。If comparand and the value in location1 are equal by reference, then value is stored in location1. それ以外の場合は演算が実行されません。Otherwise, no operation is performed. 比較と交換は、分割不可能な操作として実行されます。The comparison and the exchange are performed as an atomic operation. このメソッドの戻り値は、交換が行われるlocation1かどうかにかかわらず、の元の値です。The return value of this method is the original value in location1, whether or not the exchange takes place.

このメソッドは、参照型のみをサポートします。This method only supports reference types. CompareExchange値型IntPtr 、、Double、 、およびのメソッドのオーバーロードがありますが、その他の値型はサポートされていません。Single Int32 Int64There are overloads of the CompareExchange method for the value types Int32, Int64, IntPtr, Single, and Double, but there is no support for other value types.

注意

後者では、変換先のCompareExchange(Object, Object, Object)オブジェクトに遅延バインディングでアクセスする必要があるため、このメソッドオーバーロードはメソッドのオーバーロードに適しています。This method overload is preferable to the CompareExchange(Object, Object, Object) method overload, because the latter requires the destination object to be accessed late-bound.

適用対象