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

Definizione

Confronta due valori per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.Compares two values for equality and, if they are equal, replaces the first value.

Overload

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

Confronta due numeri a virgola mobile e precisione doppia per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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)

Confronta due interi con segno a 32 bit per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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)

Confronta due interi con segno a 64 bit per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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)

Confronta due puntatori o handle specifici della piattaforma per verificarne l'uguaglianza. Se sono uguali, sostituisce il primo elemento.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)

Confronta due oggetti per verificarne l'uguaglianza dei riferimenti. Se sono uguali, sostituisce il primo oggetto.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)

Confronta due numeri a virgola mobile e precisione singola per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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)

Confronta due istanze del tipo di riferimento T specificato per verificarne l'uguaglianza dei riferimenti. Se sono uguali, sostituisce la prima istanza.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)

Confronta due numeri a virgola mobile e precisione doppia per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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

Parametri

location1
Double Double Double Double

Destinazione il cui valore viene confrontato con comparand ed eventualmente sostituito.The destination, whose value is compared with comparand and possibly replaced.

value
Double Double Double Double

Valore che sostituisce il valore di destinazione se il confronto rileva l'uguaglianza.The value that replaces the destination value if the comparison results in equality.

comparand
Double Double Double Double

Valore confrontato con il valore in corrispondenza di location1.The value that is compared to the value at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Esempi

Nell'esempio di codice seguente viene illustrato un metodo thread-safe che accumula un totale parziale Double di valori.The following code example demonstrates a thread-safe method that accumulates a running total of Double values. Due thread aggiungono una serie Double di valori usando il metodo thread-safe e l'aggiunta ordinaria e, quando i thread completano i totali, vengono confrontati.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. In un computer a doppio processore esiste una differenza significativa nei totali.On a dual-processor computer, there is a significant difference in the totals.

Nel metodo thread-safe il valore iniziale del totale parziale viene salvato, quindi il CompareExchange metodo viene usato per scambiare il totale appena calcolato con il totale precedente.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. Se il valore restituito non è uguale al valore salvato del totale parziale, un altro thread ha aggiornato il totale nel frattempo.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. In tal caso, è necessario ripetere il tentativo di aggiornamento del totale parziale.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

Commenti

Se comparand e il valore in location1 sono uguali, value viene archiviato in location1.If comparand and the value in location1 are equal, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di CompareExchange è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Vedi anche

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

Confronta due interi con segno a 32 bit per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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

Parametri

location1
Int32 Int32 Int32 Int32

Destinazione il cui valore viene confrontato con comparand ed eventualmente sostituito.The destination, whose value is compared with comparand and possibly replaced.

value
Int32 Int32 Int32 Int32

Valore che sostituisce il valore di destinazione se il confronto rileva l'uguaglianza.The value that replaces the destination value if the comparison results in equality.

comparand
Int32 Int32 Int32 Int32

Valore confrontato con il valore in corrispondenza di location1.The value that is compared to the value at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Esempi

Nell'esempio di codice riportato di seguito viene illustrato un metodo thread-safe che accumula un totale parziale.The following code example demonstrates a thread-safe method that accumulates a running total. Il valore iniziale del totale parziale viene salvato, quindi il CompareExchange metodo viene usato per scambiare il totale appena calcolato con il totale precedente.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. Se il valore restituito non è uguale al valore salvato del totale parziale, un altro thread ha aggiornato il totale nel frattempo.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. In tal caso, è necessario ripetere il tentativo di aggiornamento del totale parziale.In that case, the attempt to update the running total must be repeated.

Nota

Il Add metodo, introdotto nella versione 2,0 della .NET Framework, fornisce un modo più pratico per accumulare i totali di esecuzione thread-safe per i numeri interi.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

Commenti

Se comparand e il valore in location1 sono uguali, value viene archiviato in location1.If comparand and the value in location1 are equal, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di CompareExchange è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Vedi anche

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

Confronta due interi con segno a 64 bit per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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

Parametri

location1
Int64 Int64 Int64 Int64

Destinazione il cui valore viene confrontato con comparand ed eventualmente sostituito.The destination, whose value is compared with comparand and possibly replaced.

value
Int64 Int64 Int64 Int64

Valore che sostituisce il valore di destinazione se il confronto rileva l'uguaglianza.The value that replaces the destination value if the comparison results in equality.

comparand
Int64 Int64 Int64 Int64

Valore confrontato con il valore in corrispondenza di location1.The value that is compared to the value at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Commenti

Se comparand e il valore in location1 sono uguali, value viene archiviato in location1.If comparand and the value in location1 are equal, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di CompareExchange è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Vedi anche

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

Confronta due puntatori o handle specifici della piattaforma per verificarne l'uguaglianza. Se sono uguali, sostituisce il primo elemento.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

Parametri

location1
IntPtr IntPtr IntPtr IntPtr

IntPtr di destinazione, il cui valore viene confrontato con il valore di comparand e, se possibile, sostituito da value.The destination IntPtr, whose value is compared with the value of comparand and possibly replaced by value.

value
IntPtr IntPtr IntPtr IntPtr

IntPtr che sostituisce il valore di destinazione se il confronto rileva l'uguaglianza.The IntPtr that replaces the destination value if the comparison results in equality.

comparand
IntPtr IntPtr IntPtr IntPtr

IntPtr da confrontare al valore in corrispondenza di location1.The IntPtr that is compared to the value at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Commenti

Se comparand e il valore in location1 sono uguali, value viene archiviato in location1.If comparand and the value in location1 are equal, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di questo metodo è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of this method is the original value in location1, whether or not the exchange takes place.

Nota

IntPtrè un tipo specifico della piattaforma.IntPtr is a platform-specific type.

Vedi anche

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

Confronta due oggetti per verificarne l'uguaglianza dei riferimenti. Se sono uguali, sostituisce il primo oggetto.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

Parametri

location1
Object Object Object Object

Oggetto di destinazione confrontato per riferimento con comparand ed eventualmente sostituito.The destination object that is compared by reference with comparand and possibly replaced.

value
Object Object Object Object

Oggetto che sostituisce l'oggetto di destinazione se il confronto dei riferimenti rileva l'uguaglianza.The object that replaces the destination object if the reference comparison results in equality.

comparand
Object Object Object Object

Oggetto confrontato per riferimento con l'oggetto in location1.The object that is compared by reference to the object at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Commenti

Importante

A partire da .NET Framework 2.0, l'overload del metodo CompareExchange<T>(T, T, T) offre un'alternativa indipendente dai tipi per i tipo di riferimento.Beginning with .NET Framework 2.0, the CompareExchange<T>(T, T, T) method overload provides a type-safe alternative for reference types. È consigliabile chiamarlo invece di questo overload.We recommend that you call it instead of this overload.

Se comparand e l'oggetto in location1 sono value uguali per riferimento, viene archiviato in location1.If comparand and the object in location1 are equal by reference, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di CompareExchange è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Nota

Gli oggetti vengono confrontati per l'uguaglianza dei riferimenti anziché per l'uguaglianza dei valori.The objects are compared for reference equality rather than value equality. Di conseguenza, due istanze boxed dello stesso tipo di valore, ad esempio il numero intero 3, sembrano sempre non uguali e non viene eseguita alcuna operazione.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. Non usare questo overload con i tipi di valore.Do not use this overload with value types.

Vedi anche

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

Confronta due numeri a virgola mobile e precisione singola per verificarne l'uguaglianza; se sono uguali, sostituisce il primo valore.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

Parametri

location1
Single Single Single Single

Destinazione il cui valore viene confrontato con comparand ed eventualmente sostituito.The destination, whose value is compared with comparand and possibly replaced.

value
Single Single Single Single

Valore che sostituisce il valore di destinazione se il confronto rileva l'uguaglianza.The value that replaces the destination value if the comparison results in equality.

comparand
Single Single Single Single

Valore confrontato con il valore in corrispondenza di location1.The value that is compared to the value at location1.

Restituisce

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Esempi

Nell'esempio di codice seguente viene illustrato un metodo thread-safe che accumula un totale parziale Single di valori.The following code example demonstrates a thread-safe method that accumulates a running total of Single values. Due thread aggiungono una serie Single di valori usando il metodo thread-safe e l'aggiunta ordinaria e, quando i thread completano i totali, vengono confrontati.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. In un computer a doppio processore esiste una differenza significativa nei totali.On a dual-processor computer, there is a significant difference in the totals.

Nel metodo thread-safe il valore iniziale del totale parziale viene salvato, quindi il CompareExchange metodo viene usato per scambiare il totale appena calcolato con il totale precedente.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. Se il valore restituito non è uguale al valore salvato del totale parziale, un altro thread ha aggiornato il totale nel frattempo.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. In tal caso, è necessario ripetere il tentativo di aggiornamento del totale parziale.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

Commenti

Se comparand e il valore in location1 sono uguali, value viene archiviato in location1.If comparand and the value in location1 are equal, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Le operazioni di confronto e scambio vengono eseguite come operazione atomica.The compare and exchange operations are performed as an atomic operation. Il valore restituito di CompareExchange è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Vedi anche

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

Confronta due istanze del tipo di riferimento T specificato per verificarne l'uguaglianza dei riferimenti. Se sono uguali, sostituisce la prima istanza.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

Parametri di tipo

T

Tipo da utilizzare per location1, value e comparand.The type to be used for location1, value, and comparand. Questo tipo deve essere un tipo di riferimento.This type must be a reference type.

Parametri

location1
T T T T

Destinazione il cui valore viene confrontato per riferimento con comparand ed eventualmente sostituito.The destination, whose value is compared by reference with comparand and possibly replaced. Questo rappresenta un parametro di riferimento (ref in C#, ByRef in Visual Basic).This is a reference parameter (ref in C#, ByRef in Visual Basic).

value
T T T T

Valore che sostituisce il valore di destinazione se il confronto dei riferimenti rileva l'uguaglianza.The value that replaces the destination value if the comparison by reference results in equality.

comparand
T T T T

Valore confrontato per riferimento con il valore in location1.The value that is compared by reference to the value at location1.

Restituisce

T T T T

Valore originale in location1.The original value in location1.

Eccezioni

L'indirizzo di location1 è un puntatore Null.The address of location1 is a null pointer.

Commenti

Se comparand e il valore in location1 sono value uguali per riferimento, viene archiviato in location1.If comparand and the value in location1 are equal by reference, then value is stored in location1. In caso contrario, non viene eseguita alcuna operazione.Otherwise, no operation is performed. Il confronto e lo scambio vengono eseguiti come operazione atomica.The comparison and the exchange are performed as an atomic operation. Il valore restituito di questo metodo è il valore originale in location1, indipendentemente dal fatto che lo scambio avvenga o meno.The return value of this method is the original value in location1, whether or not the exchange takes place.

Questo metodo supporta solo i tipi di riferimento.This method only supports reference types. Sono disponibili overload del CompareExchange metodo per i tipi Int32di valore, Single Int64 IntPtr,, e Double, ma non è disponibile alcun supporto per altri tipi di valore.There 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.

Nota

Questo overload del metodo è preferibile CompareExchange(Object, Object, Object) all'overload del metodo, perché quest'ultimo richiede l'accesso ad associazione tardiva all'oggetto di destinazione.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.

Si applica a