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

Определение

Сравнивает два значения на равенство и, если они равны, заменяет первое.Compares two values for equality and, if they are equal, replaces the first value.

Перегрузки

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

Сравнивает два числа с плавающей запятой двойной точности на равенство и заменяет первое значение, если они равны.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)

Сравнивает два 32-разрядных целых числа со знаком на равенство и заменяет первое, если они равны.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)

Сравнивает два 64-разрядных целых числа со знаком на равенство и заменяет первое, если они равны.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)

Сравнивает два зависящих от платформы обработчика или указателя на равенство и заменяет первое из значений, если они равны.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)

Сравнивает два объекта на равенство ссылок и заменяет первый объект, если они равны.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)

Сравнивает два числа с плавающей запятой с обычной точностью на равенство и, если они равны, заменяет первое значение.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)

Сравнивает два экземпляра указанного ссылочного типа T на равенство ссылок. Если они равны, заменяет первый экземпляр.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)

Сравнивает два числа с плавающей запятой двойной точности на равенство и заменяет первое значение, если они равны.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

Параметры

location1
Double Double Double Double

Целевой объект, который нужно сравнить с объектом comparand и, возможно, заменить.The destination, whose value is compared with comparand and possibly replaced.

value
Double Double Double Double

Значение, которым будет заменено целевое значение, если проверка покажет равенство.The value that replaces the destination value if the comparison results in equality.

comparand
Double Double Double Double

Значение, которое сравнивается со значением в позиции location1.The value that is compared to the value at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Примеры

В следующем примере кода демонстрируется поточно-ориентированный метод, выполняющий накопленное Double итоговое значение.The following code example demonstrates a thread-safe method that accumulates a running total of Double values. Два потока добавляют ряд Double значений с помощью потокобезопасного метода и обычного сложения, а также при сравнении потоков с итогами.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. На компьютере с двумя процессорами значительная разница в итогах.On a dual-processor computer, there is a significant difference in the totals.

В поточно-ориентированном методе сохраняется начальное значение итогового значения, а затем CompareExchange метод используется для обмена только что вычисленным итогом со старым итогом.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. Если возвращаемое значение не равно сохраненному значению итогового значения, то другой поток в то же время обновил итог.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. В этом случае попытка обновления итогового значения должна быть повторена.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

Комментарии

Если comparand и значение в location1 равны, то value хранится в location1.If comparand and the value in location1 are equal, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение CompareExchange является исходным значением в location1, независимо от того, происходит ли обмен.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Дополнительно

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

Сравнивает два 32-разрядных целых числа со знаком на равенство и заменяет первое, если они равны.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

Параметры

location1
Int32 Int32 Int32 Int32

Целевой объект, который нужно сравнить с объектом comparand и, возможно, заменить.The destination, whose value is compared with comparand and possibly replaced.

value
Int32 Int32 Int32 Int32

Значение, которым будет заменено целевое значение, если проверка покажет равенство.The value that replaces the destination value if the comparison results in equality.

comparand
Int32 Int32 Int32 Int32

Значение, которое сравнивается со значением в позиции location1.The value that is compared to the value at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Примеры

В следующем примере кода демонстрируется потокобезопасный метод, который накапливает итоговое значение.The following code example demonstrates a thread-safe method that accumulates a running total. Исходное значение итогового значения сохраняется, а затем CompareExchange метод используется для обмена только что вычисленным итогом со старым итогом.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. Если возвращаемое значение не равно сохраненному значению итогового значения, то другой поток в то же время обновил итог.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. В этом случае попытка обновления итогового значения должна быть повторена.In that case, the attempt to update the running total must be repeated.

Примечание

Add Метод, представленный в версии 2,0 .NET Framework, предоставляет более удобный способ накопления поточно-ориентированных итогов для целых чисел.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

Комментарии

Если comparand и значение в location1 равны, то value хранится в location1.If comparand and the value in location1 are equal, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение CompareExchange является исходным значением в location1, независимо от того, происходит ли обмен.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Дополнительно

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

Сравнивает два 64-разрядных целых числа со знаком на равенство и заменяет первое, если они равны.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

Параметры

location1
Int64 Int64 Int64 Int64

Целевой объект, который нужно сравнить с объектом comparand и, возможно, заменить.The destination, whose value is compared with comparand and possibly replaced.

value
Int64 Int64 Int64 Int64

Значение, которым будет заменено целевое значение, если проверка покажет равенство.The value that replaces the destination value if the comparison results in equality.

comparand
Int64 Int64 Int64 Int64

Значение, которое сравнивается со значением в позиции location1.The value that is compared to the value at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Комментарии

Если comparand и значение в location1 равны, то value хранится в location1.If comparand and the value in location1 are equal, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение CompareExchange является исходным значением в location1, независимо от того, происходит ли обмен.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Дополнительно

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

Сравнивает два зависящих от платформы обработчика или указателя на равенство и заменяет первое из значений, если они равны.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

Параметры

location1
IntPtr IntPtr IntPtr IntPtr

Целевое значение IntPtr, которое будет сравниваться со значением параметра comparand и, возможно, будет заменено value.The destination IntPtr, whose value is compared with the value of comparand and possibly replaced by value.

value
IntPtr IntPtr IntPtr IntPtr

Значение IntPtr, которое заменит целевое значение, если результатом сравнения будет равенство.The IntPtr that replaces the destination value if the comparison results in equality.

comparand
IntPtr IntPtr IntPtr IntPtr

Значение IntPtr, которое сравнивается со значением location1.The IntPtr that is compared to the value at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Комментарии

Если comparand и значение в location1 равны, то value хранится в location1.If comparand and the value in location1 are equal, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение этого метода является исходным значением в location1, независимо от того, происходит ли обмен.The return value of this method is the original value in location1, whether or not the exchange takes place.

Примечание

IntPtr— Это тип, зависящий от платформы.IntPtr is a platform-specific type.

Дополнительно

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

Сравнивает два объекта на равенство ссылок и заменяет первый объект, если они равны.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

Параметры

location1
Object Object Object Object

Целевой объект, который будет сравниваться по ссылке со значением параметра comparand и, возможно, будет заменен.The destination object that is compared by reference with comparand and possibly replaced.

value
Object Object Object Object

Объект, который заменит целевой объект, если результатом сравнения по ссылке будет равенство.The object that replaces the destination object if the reference comparison results in equality.

comparand
Object Object Object Object

Объект, который сравнивается по ссылке с объектом в location1.The object that is compared by reference to the object at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Комментарии

Важно!

Начиная с .NET Framework 2.0 перегрузка метода CompareExchange<T>(T, T, T) предоставляет типобезопасную альтернативу для ссылочных типов.Beginning with .NET Framework 2.0, the CompareExchange<T>(T, T, T) method overload provides a type-safe alternative for reference types. Рекомендуется вызывать его вместо этой перегрузки.We recommend that you call it instead of this overload.

Если comparand и объект в location1 равны по ссылке, то value хранится в location1.If comparand and the object in location1 are equal by reference, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение CompareExchange является исходным значением в location1, независимо от того, происходит ли обмен.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Примечание

Объекты сравниваются на равенство ссылок, а не на равенство значений.The objects are compared for reference equality rather than value equality. В результате два упакованных экземпляра одного и того же типа значения (например, целое число 3) всегда выглядят неравными и никакие операции не выполняются.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. Не используйте эту перегрузку с типами значений.Do not use this overload with value types.

Дополнительно

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

Сравнивает два числа с плавающей запятой с обычной точностью на равенство и, если они равны, заменяет первое значение.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

Параметры

location1
Single Single Single Single

Целевой объект, который нужно сравнить с объектом comparand и, возможно, заменить.The destination, whose value is compared with comparand and possibly replaced.

value
Single Single Single Single

Значение, которым будет заменено целевое значение, если проверка покажет равенство.The value that replaces the destination value if the comparison results in equality.

comparand
Single Single Single Single

Значение, которое сравнивается со значением в позиции location1.The value that is compared to the value at location1.

Возвраты

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Примеры

В следующем примере кода демонстрируется поточно-ориентированный метод, выполняющий накопленное Single итоговое значение.The following code example demonstrates a thread-safe method that accumulates a running total of Single values. Два потока добавляют ряд Single значений с помощью потокобезопасного метода и обычного сложения, а также при сравнении потоков с итогами.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. На компьютере с двумя процессорами значительная разница в итогах.On a dual-processor computer, there is a significant difference in the totals.

В поточно-ориентированном методе сохраняется начальное значение итогового значения, а затем CompareExchange метод используется для обмена только что вычисленным итогом со старым итогом.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. Если возвращаемое значение не равно сохраненному значению итогового значения, то другой поток в то же время обновил итог.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. В этом случае попытка обновления итогового значения должна быть повторена.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

Комментарии

Если comparand и значение в location1 равны, то value хранится в location1.If comparand and the value in location1 are equal, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Операции сравнения и обмена выполняются в виде атомарной операции.The compare and exchange operations are performed as an atomic operation. Возвращаемое значение CompareExchange является исходным значением в location1, независимо от того, происходит ли обмен.The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

Дополнительно

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

Сравнивает два экземпляра указанного ссылочного типа T на равенство ссылок. Если они равны, заменяет первый экземпляр.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

Параметры типа

T

Тип, используемый для location1, value, и comparand.The type to be used for location1, value, and comparand. Этот тип должен быть ссылочным типом.This type must be a reference type.

Параметры

location1
T T T T

Целевой объект, значение которого сравнивается по ссылке с объектом comparand и, возможно, будет заменено.The destination, whose value is compared by reference with comparand and possibly replaced. Это ссылочный параметр (ref в C#, ByRef в Visual Basic).This is a reference parameter (ref in C#, ByRef in Visual Basic).

value
T T T T

Значение, которым будет заменено целевое значение, если результатом сравнения по ссылке будет равенство.The value that replaces the destination value if the comparison by reference results in equality.

comparand
T T T T

Значение, которое сравнивается по ссылке со значением в позиции location1.The value that is compared by reference to the value at location1.

Возвраты

T T T T

Исходное значение в позиции location1.The original value in location1.

Исключения

Адрес location1 является пустым указателем.The address of location1 is a null pointer.

Комментарии

Если comparand и значение в location1 равны по ссылке, то value хранится в location1.If comparand and the value in location1 are equal by reference, then value is stored in location1. В противном случае операция не выполняется.Otherwise, no operation is performed. Сравнение и обмен выполняются как атомарная операция.The comparison and the exchange are performed as an atomic operation. Возвращаемое значение этого метода является исходным значением в location1, независимо от того, происходит ли обмен.The return value of this method is the original value in location1, whether or not the exchange takes place.

Этот метод поддерживает только ссылочные типы.This method only supports reference types. Существуют перегрузки CompareExchange метода для типов Single Int64 Int32значений, IntPtr,, и Double, но отсутствует поддержка других типов значений.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.

Примечание

Этот перегруженный метод является предпочтительным для CompareExchange(Object, Object, Object) перегрузки метода, так как последний требует, чтобы целевой объект осуществлял доступ с поздней привязкой.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.

Применяется к