Interlocked.Exchange Interlocked.Exchange Interlocked.Exchange Interlocked.Exchange Method

Definition

Sets a variable to a specified value as an atomic operation.

Overloads

Exchange(Single, Single) Exchange(Single, Single) Exchange(Single, Single) Exchange(Single, Single)

Sets a single-precision floating point number to a specified value and returns the original value, as an atomic operation.

Exchange(Object, Object) Exchange(Object, Object) Exchange(Object, Object) Exchange(Object, Object)

Sets an object to a specified value and returns a reference to the original object, as an atomic operation.

Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr)

Sets a platform-specific handle or pointer to a specified value and returns the original value, as an atomic operation.

Exchange(Double, Double) Exchange(Double, Double) Exchange(Double, Double) Exchange(Double, Double)

Sets a double-precision floating point number to a specified value and returns the original value, as an atomic operation.

Exchange(Int32, Int32) Exchange(Int32, Int32) Exchange(Int32, Int32) Exchange(Int32, Int32)

Sets a 32-bit signed integer to a specified value and returns the original value, as an atomic operation.

Exchange(Int64, Int64) Exchange(Int64, Int64) Exchange(Int64, Int64) Exchange(Int64, Int64)

Sets a 64-bit signed integer to a specified value and returns the original value, as an atomic operation.

Exchange<T>(T, T) Exchange<T>(T, T) Exchange<T>(T, T) Exchange<T>(T, T)

Sets a variable of the specified type T to a specified value and returns the original value, as an atomic operation.

Exchange(Single, Single) Exchange(Single, Single) Exchange(Single, Single) Exchange(Single, Single)

Sets a single-precision floating point number to a specified value and returns the original value, as an atomic operation.

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

The variable to set to the specified value.

value
Single Single Single Single

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Exchange(Object, Object) Exchange(Object, Object) Exchange(Object, Object) Exchange(Object, Object)

Sets an object to a specified value and returns a reference to the original object, as an atomic operation.

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

The variable to set to the specified value.

value
Object Object Object Object

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Remarks

Note

Beginning with .NET Framework version 2.0, the Exchange<T>(T, T) method overload provides a type-safe alternative for reference types.

Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr) Exchange(IntPtr, IntPtr)

Sets a platform-specific handle or pointer to a specified value and returns the original value, as an atomic operation.

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

The variable to set to the specified value.

value
IntPtr IntPtr IntPtr IntPtr

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Exchange(Double, Double) Exchange(Double, Double) Exchange(Double, Double) Exchange(Double, Double)

Sets a double-precision floating point number to a specified value and returns the original value, as an atomic operation.

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

The variable to set to the specified value.

value
Double Double Double Double

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Exchange(Int32, Int32) Exchange(Int32, Int32) Exchange(Int32, Int32) Exchange(Int32, Int32)

Sets a 32-bit signed integer to a specified value and returns the original value, as an atomic operation.

public:
 static int Exchange(int % location1, int value);
public static int Exchange (ref int location1, int value);
static member Exchange :  * int -> int
Public Shared Function Exchange (ByRef location1 As Integer, value As Integer) As Integer
Parameters
location1
Int32 Int32 Int32 Int32

The variable to set to the specified value.

value
Int32 Int32 Int32 Int32

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Examples

The following code example shows a thread-safe resource locking mechanism.

using namespace System;
using namespace System::Threading;

const int numThreads = 10;
const int numThreadIterations = 5;
ref class MyInterlockedExchangeExampleClass
{
public:
   static void MyThreadProc()
   {
      for ( int i = 0; i < numThreadIterations; i++ )
      {
         UseResource();
         
         //Wait 1 second before next attempt.
         Thread::Sleep( 1000 );

      }
   }


private:
   //A simple method that denies reentrancy.
   static bool UseResource()
   {
      
      //0 indicates that the method is not in use.
      if ( 0 == Interlocked::Exchange( usingResource, 1 ) )
      {
         Console::WriteLine( " {0} acquired the lock", Thread::CurrentThread->Name );
         
         //Code to access a resource that is not thread safe would go here.
         //Simulate some work
         Thread::Sleep( 500 );
         Console::WriteLine( " {0} exiting lock", Thread::CurrentThread->Name );
         
         //Release the lock
         Interlocked::Exchange( usingResource, 0 );
         return true;
      }
      else
      {
         Console::WriteLine( " {0} was denied the lock", Thread::CurrentThread->Name );
         return false;
      }
   }


   //0 for false, 1 for true.
   static int usingResource;
};

int main()
{
   Thread^ myThread;
   Random^ rnd = gcnew Random;
   for ( int i = 0; i < numThreads; i++ )
   {
      myThread = gcnew Thread( gcnew ThreadStart( MyInterlockedExchangeExampleClass::MyThreadProc ) );
      myThread->Name = String::Format( "Thread {0}", i + 1 );
      
      //Wait a random amount of time before starting next thread.
      Thread::Sleep( rnd->Next( 0, 1000 ) );
      myThread->Start();

   }
}

using System;
using System.Threading;

namespace InterlockedExchange_Example
{
    class MyInterlockedExchangeExampleClass
    {
        //0 for false, 1 for true.
        private static int usingResource = 0;

        private const int numThreadIterations = 5;
        private const int numThreads = 10;

        static void Main()
        {
            Thread myThread;
            Random rnd = new Random();

            for(int i = 0; i < numThreads; i++)
            {
                myThread = new Thread(new ThreadStart(MyThreadProc));
                myThread.Name = String.Format("Thread{0}", i + 1);
            
                //Wait a random amount of time before starting next thread.
                Thread.Sleep(rnd.Next(0, 1000));
                myThread.Start();
            }
        }

        private static void MyThreadProc()
        {
            for(int i = 0; i < numThreadIterations; i++)
            {
                UseResource();
            
                //Wait 1 second before next attempt.
                Thread.Sleep(1000);
            }
        }

        //A simple method that denies reentrancy.
        static bool UseResource()
        {
            //0 indicates that the method is not in use.
            if(0 == Interlocked.Exchange(ref usingResource, 1))
            {
                Console.WriteLine("{0} acquired the lock", Thread.CurrentThread.Name);
            
                //Code to access a resource that is not thread safe would go here.
            
                //Simulate some work
                Thread.Sleep(500);

                Console.WriteLine("{0} exiting lock", Thread.CurrentThread.Name);
            
                //Release the lock
                Interlocked.Exchange(ref usingResource, 0);
                return true;
            }
            else
            {
                Console.WriteLine("   {0} was denied the lock", Thread.CurrentThread.Name);
                return false;
            }
        }

    }
}  
Imports System
Imports System.Threading

Namespace InterlockedExchange_Example
    Class MyInterlockedExchangeExampleClass
        '0 for false, 1 for true.
        Private Shared usingResource As Integer = 0

        Private Const numThreadIterations As Integer = 5
        Private Const numThreads As Integer = 10

        <MTAThread> _
        Shared Sub Main()
            Dim myThread As Thread
            Dim rnd As New Random()

            Dim i As Integer
            For i = 0 To numThreads - 1
                myThread = New Thread(AddressOf MyThreadProc)
                myThread.Name = String.Format("Thread{0}", i + 1)

                'Wait a random amount of time before starting next thread.
                Thread.Sleep(rnd.Next(0, 1000))
                myThread.Start()
            Next i
        End Sub 'Main

        Private Shared Sub MyThreadProc()
            Dim i As Integer
            For i = 0 To numThreadIterations - 1
                UseResource()

                'Wait 1 second before next attempt.
                Thread.Sleep(1000)
            Next i
        End Sub 

        'A simple method that denies reentrancy.
        Shared Function UseResource() As Boolean
            '0 indicates that the method is not in use.
            If 0 = Interlocked.Exchange(usingResource, 1) Then
                Console.WriteLine("{0} acquired the lock", Thread.CurrentThread.Name)

                'Code to access a resource that is not thread safe would go here.
                'Simulate some work
                Thread.Sleep(500)

                Console.WriteLine("{0} exiting lock", Thread.CurrentThread.Name)

                'Release the lock
                Interlocked.Exchange(usingResource, 0)
                Return True
            Else
                Console.WriteLine("   {0} was denied the lock", Thread.CurrentThread.Name)
                Return False
            End If
        End Function 
    End Class 
End Namespace 

Exchange(Int64, Int64) Exchange(Int64, Int64) Exchange(Int64, Int64) Exchange(Int64, Int64)

Sets a 64-bit signed integer to a specified value and returns the original value, as an atomic operation.

public:
 static long Exchange(long % location1, long value);
public static long Exchange (ref long location1, long value);
static member Exchange :  * int64 -> int64
Public Shared Function Exchange (ByRef location1 As Long, value As Long) As Long
Parameters
location1
Int64 Int64 Int64 Int64

The variable to set to the specified value.

value
Int64 Int64 Int64 Int64

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Exchange<T>(T, T) Exchange<T>(T, T) Exchange<T>(T, T) Exchange<T>(T, T)

Sets a variable of the specified type T to a specified value and returns the original value, as an atomic operation.

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

The type to be used for location1 and value. This type must be a reference type.

Parameters
location1

The variable to set to the specified value. This is a reference parameter (ref in C#, ByRef in Visual Basic).

value

The value to which the location1 parameter is set.

Returns

The original value of location1.

Exceptions

Remarks

This method only supports reference types. There are overloads of the Exchange method for the Int32, Int64, IntPtr, Single, and Double value types, but there is no support for other value types.

Note

This method overload is preferable to the Exchange(Object, Object) method overload, because the latter requires late-bound access to the destination object .

Applies to