Interlocked.CompareExchange Método

Definición

Compara dos valores para comprobar si son iguales y, si lo son, reemplaza el primer valor.Compares two values for equality and, if they are equal, replaces the first value.

Sobrecargas

CompareExchange(UInt64, UInt64, UInt64)

Compara los dos enteros sin signo de 64 bits para determinar si son iguales y, si lo son, reemplaza el primer valor.Compares two 64-bit unsigned integers for equality and, if they are equal, replaces the first value.

CompareExchange(UInt32, UInt32, UInt32)

Compara los dos enteros sin signo de 32 bits para determinar si son iguales y, si lo son, reemplaza el primer valor.Compares two 32-bit unsigned integers for equality and, if they are equal, replaces the first value.

CompareExchange(Single, Single, Single)

Compara dos números de punto flotante de precisión sencilla para comprobar si son iguales y, si lo son, reemplaza el primero de los valores.Compares two single-precision floating point numbers for equality and, if they are equal, replaces the first value.

CompareExchange(Object, Object, Object)

Compara dos objetos en términos de igualdad de referencia y, si son iguales, reemplaza el primero.Compares two objects for reference equality and, if they are equal, replaces the first object.

CompareExchange(Int64, Int64, Int64)

Compara dos enteros de 64 bits con signo para comprobar si son iguales y, si lo son, reemplaza el primer valor.Compares two 64-bit signed integers for equality and, if they are equal, replaces the first value.

CompareExchange(Int32, Int32, Int32)

Compara dos enteros de 32 bits con signo para comprobar si son iguales y, si lo son, reemplaza el primer valor.Compares two 32-bit signed integers for equality and, if they are equal, replaces the first value.

CompareExchange(Double, Double, Double)

Compara dos números de punto flotante de precisión doble para comprobar si son iguales y, si lo son, reemplaza el primero de los valores.Compares two double-precision floating point numbers for equality and, if they are equal, replaces the first value.

CompareExchange(IntPtr, IntPtr, IntPtr)

Compara dos identificadores o punteros específicos de la plataforma en términos de igualdad y, si son iguales, reemplaza el primero.Compares two platform-specific handles or pointers for equality and, if they are equal, replaces the first one.

CompareExchange<T>(T, T, T)

Compara dos instancias del tipo de referencia especificado T para comprobar si las referencias son iguales y, si lo son, reemplaza la primera.Compares two instances of the specified reference type T for reference equality and, if they are equal, replaces the first one.

CompareExchange(UInt64, UInt64, UInt64)

Compara los dos enteros sin signo de 64 bits para determinar si son iguales y, si lo son, reemplaza el primer valor.Compares two 64-bit unsigned integers for equality and, if they are equal, replaces the first value.

public:
 static System::UInt64 CompareExchange(System::UInt64 % location1, System::UInt64 value, System::UInt64 comparand);
public static ulong CompareExchange (ref ulong location1, ulong value, ulong comparand);
static member CompareExchange : uint64 * uint64 * uint64 -> uint64
Public Shared Function CompareExchange (ByRef location1 As ULong, value As ULong, comparand As ULong) As ULong

Parámetros

location1
UInt64

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
UInt64

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
UInt64

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

UInt64

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero null.The address of location1 is a null pointer.

Se aplica a

CompareExchange(UInt32, UInt32, UInt32)

Compara los dos enteros sin signo de 32 bits para determinar si son iguales y, si lo son, reemplaza el primer valor.Compares two 32-bit unsigned integers for equality and, if they are equal, replaces the first value.

public:
 static System::UInt32 CompareExchange(System::UInt32 % location1, System::UInt32 value, System::UInt32 comparand);
public static uint CompareExchange (ref uint location1, uint value, uint comparand);
static member CompareExchange : uint32 * uint32 * uint32 -> uint32
Public Shared Function CompareExchange (ByRef location1 As UInteger, value As UInteger, comparand As UInteger) As UInteger

Parámetros

location1
UInt32

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
UInt32

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
UInt32

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

UInt32

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero null.The address of location1 is a null pointer.

Se aplica a

CompareExchange(Single, Single, Single)

Compara dos números de punto flotante de precisión sencilla para comprobar si son iguales y, si lo son, reemplaza el primero de los valores.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

Parámetros

location1
Single

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
Single

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
Single

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

Single

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Ejemplos

En el ejemplo de código siguiente se muestra un método seguro para subprocesos que acumula un total de valores en ejecución Single .The following code example demonstrates a thread-safe method that accumulates a running total of Single values. Dos subprocesos agregan una serie de Single valores mediante el método seguro para subprocesos y la adición ordinaria, y cuando los subprocesos completan los totales se comparan.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. En un equipo con doble procesador, existe una diferencia significativa en los totales.On a dual-processor computer, there is a significant difference in the totals.

En el método seguro para subprocesos, el valor inicial del total en ejecución se guarda y, a continuación, el CompareExchange método se usa para intercambiar el total calculado recientemente con el total anterior.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. Si el valor devuelto no es igual al valor guardado del total acumulado, otro subproceso ha actualizado el total mientras tanto.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. En ese caso, se debe repetir el intento de actualizar el total en ejecución.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

Comentarios

Si comparand y el valor de location1 son iguales, value se almacena en location1 .If comparand and the value in location1 are equal, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de CompareExchange es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Consulte también

Se aplica a

CompareExchange(Object, Object, Object)

Compara dos objetos en términos de igualdad de referencia y, si son iguales, reemplaza el primero.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

Parámetros

location1
Object

Objeto de destino que se compara por referencia con comparand y que posiblemente se reemplace.The destination object that is compared by reference with comparand and possibly replaced.

value
Object

Objeto que reemplaza el objeto de destino si la comparación de referencia da como resultado la igualdad de ambos parámetros.The object that replaces the destination object if the reference comparison results in equality.

comparand
Object

Objeto que se compara por referencia con el objeto que hay en location1.The object that is compared by reference to the object at location1.

Devoluciones

Object

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero null.The address of location1 is a null pointer.

La dirección de location1 es un puntero null.The address of location1 is a null pointer.

Comentarios

Importante

A partir de .NET Framework 2.0, la sobrecarga del método CompareExchange<T>(T, T, T) proporciona una alternativa de seguridad de tipos para tipos de referencia.Beginning with .NET Framework 2.0, the CompareExchange<T>(T, T, T) method overload provides a type-safe alternative for reference types. Se recomienda llamarlo en lugar de esta sobrecarga.We recommend that you call it instead of this overload.

Si comparand y el objeto de location1 son iguales por referencia, value se almacena en location1 .If comparand and the object in location1 are equal by reference, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de CompareExchange es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Nota

Los objetos se comparan para la igualdad de referencia en lugar de la igualdad de valores.The objects are compared for reference equality rather than value equality. Como resultado, dos instancias de conversión boxing del mismo tipo de valor (por ejemplo, el entero 3) siempre parecen ser diferentes y no se realiza ninguna operación.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. No utilice esta sobrecarga con tipos de valor.Do not use this overload with value types.

Consulte también

Se aplica a

CompareExchange(Int64, Int64, Int64)

Compara dos enteros de 64 bits con signo para comprobar si son iguales y, si lo son, reemplaza el primer valor.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

Parámetros

location1
Int64

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
Int64

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
Int64

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

Int64

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Comentarios

Si comparand y el valor de location1 son iguales, value se almacena en location1 .If comparand and the value in location1 are equal, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de CompareExchange es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Consulte también

Se aplica a

CompareExchange(Int32, Int32, Int32)

Compara dos enteros de 32 bits con signo para comprobar si son iguales y, si lo son, reemplaza el primer valor.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

Parámetros

location1
Int32

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
Int32

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
Int32

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

Int32

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Ejemplos

En el ejemplo de código siguiente se muestra un método seguro para subprocesos que acumula un total en ejecución.The following code example demonstrates a thread-safe method that accumulates a running total. Se guarda el valor inicial del total acumulado y, a continuación, CompareExchange se usa el método para intercambiar el total calculado recientemente con el total anterior.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. Si el valor devuelto no es igual al valor guardado del total acumulado, otro subproceso ha actualizado el total mientras tanto.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. En ese caso, se debe repetir el intento de actualizar el total en ejecución.In that case, the attempt to update the running total must be repeated.

Nota

El Add método, que se presentó en la versión 2,0 del .NET Framework, proporciona una manera más cómoda de acumular totales de ejecución seguros para subprocesos para enteros.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

Comentarios

Si comparand y el valor de location1 son iguales, value se almacena en location1 .If comparand and the value in location1 are equal, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de CompareExchange es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Consulte también

Se aplica a

CompareExchange(Double, Double, Double)

Compara dos números de punto flotante de precisión doble para comprobar si son iguales y, si lo son, reemplaza el primero de los valores.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

Parámetros

location1
Double

Destino, cuyo valor se compara con comparand y que posiblemente se reemplace.The destination, whose value is compared with comparand and possibly replaced.

value
Double

Valor que reemplaza el valor de destino si la comparación da como resultado una igualdad.The value that replaces the destination value if the comparison results in equality.

comparand
Double

Valor que se compara con el valor que hay en location1.The value that is compared to the value at location1.

Devoluciones

Double

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Ejemplos

En el ejemplo de código siguiente se muestra un método seguro para subprocesos que acumula un total de valores en ejecución Double .The following code example demonstrates a thread-safe method that accumulates a running total of Double values. Dos subprocesos agregan una serie de Double valores mediante el método seguro para subprocesos y la adición ordinaria, y cuando los subprocesos completan los totales se comparan.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. En un equipo con doble procesador, existe una diferencia significativa en los totales.On a dual-processor computer, there is a significant difference in the totals.

En el método seguro para subprocesos, el valor inicial del total en ejecución se guarda y, a continuación, el CompareExchange método se usa para intercambiar el total calculado recientemente con el total anterior.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. Si el valor devuelto no es igual al valor guardado del total acumulado, otro subproceso ha actualizado el total mientras tanto.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. En ese caso, se debe repetir el intento de actualizar el total en ejecución.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

Comentarios

Si comparand y el valor de location1 son iguales, value se almacena en location1 .If comparand and the value in location1 are equal, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de CompareExchange es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Consulte también

Se aplica a

CompareExchange(IntPtr, IntPtr, IntPtr)

Compara dos identificadores o punteros específicos de la plataforma en términos de igualdad y, si son iguales, reemplaza el primero.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

Parámetros

location1
IntPtr

Estructura IntPtr de destino, cuyo valor se compara con el valor de comparand y que posiblemente se reemplace por value.The destination IntPtr, whose value is compared with the value of comparand and possibly replaced by value.

value
IntPtr

Estructura IntPtr que reemplaza el valor de destino si la comparación da como resultado una igualdad.The IntPtr that replaces the destination value if the comparison results in equality.

comparand
IntPtr

Estructura IntPtr que se compara con el valor que hay en location1.The IntPtr that is compared to the value at location1.

Devoluciones

IntPtr

Valor original de location1.The original value in location1.

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Comentarios

Si comparand y el valor de location1 son iguales, value se almacena en location1 .If comparand and the value in location1 are equal, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. Las operaciones de comparación e intercambio se realizan como una operación atómica.The compare and exchange operations are performed as an atomic operation. El valor devuelto de este método es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of this method is the original value in location1, whether or not the exchange takes place.

Nota

IntPtr es un tipo específico de la plataforma.IntPtr is a platform-specific type.

Consulte también

Se aplica a

CompareExchange<T>(T, T, T)

Compara dos instancias del tipo de referencia especificado T para comprobar si las referencias son iguales y, si lo son, reemplaza la primera.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);
public static T CompareExchange<T> (ref T location1, T value, T comparand) where T : class;
[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)
[<System.Runtime.InteropServices.ComVisible(false)>]
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

Parámetros de tipo

T

Tipo que se va a utilizar para location1, value y comparand.The type to be used for location1, value, and comparand. Este tipo debe ser un tipo de referencia.This type must be a reference type.

Parámetros

location1
T

Destino cuyo valor se compara por referencia con comparand y que posiblemente se reemplace.The destination, whose value is compared by reference with comparand and possibly replaced. Este es un parámetro de referencia (ref en C#, ByRef en Visual Basic).This is a reference parameter (ref in C#, ByRef in Visual Basic).

value
T

Valor que reemplaza el valor de destino si la comparación por referencia da como resultado una igualdad.The value that replaces the destination value if the comparison by reference results in equality.

comparand
T

Valor que se compara por referencia con el que hay en location1.The value that is compared by reference to the value at location1.

Devoluciones

T

Valor original de location1.The original value in location1.

Atributos

Excepciones

La dirección de location1 es un puntero nulo.The address of location1 is a null pointer.

Comentarios

Si comparand y el valor de location1 son iguales por referencia, value se almacena en location1 .If comparand and the value in location1 are equal by reference, then value is stored in location1. De lo contrario, no se realiza ninguna operación.Otherwise, no operation is performed. La comparación y el intercambio se realizan como una operación atómica.The comparison and the exchange are performed as an atomic operation. El valor devuelto de este método es el valor original de location1 , tanto si el intercambio tiene lugar como si no.The return value of this method is the original value in location1, whether or not the exchange takes place.

Este método solo admite tipos de referencia.This method only supports reference types. Existen sobrecargas del CompareExchange método para los tipos de valor,,, Int32 Int64 IntPtr Single y Double , pero no se admiten otros tipos de valor.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

Esta sobrecarga del método es preferible a la CompareExchange(Object, Object, Object) sobrecarga del método, ya que el último requiere que se tenga acceso al objeto de destino en tiempo de ejecución.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.

Se aplica a