Interlocked.Exchange Method

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

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

Overloads

Exchange(UInt32, UInt32)	Sets a 32-bit unsigned integer to a specified value and returns the original value, as an atomic operation.
Exchange(Single, Single)	Sets a single-precision floating point number to a specified value and returns the original value, as an atomic operation.
Exchange(UIntPtr, UIntPtr)	Sets a platform-specific handle or pointer to a specified value and returns the original value, as an atomic operation.
Exchange(UInt64, UInt64)	Sets a 64-bit unsigned integer to a specified value and returns the original value, as an atomic operation.
Exchange(IntPtr, IntPtr)	Sets a platform-specific handle or pointer to a specified value and returns the original value, as an atomic operation.
Exchange(Int64, Int64)	Sets a 64-bit signed integer to a specified value and returns the original value, as an atomic operation.
Exchange(Int32, Int32)	Sets a 32-bit signed integer to a specified value and returns the original value, as an atomic operation.
Exchange(Double, Double)	Sets a double-precision floating point number to a specified value and returns the original value, as an atomic operation.
Exchange(Object, Object)	Sets an object to a specified value and returns a reference to the original object, as an atomic operation.
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(UInt32, UInt32)

Source:

Interlocked.cs

Important

This API is not CLS-compliant.

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

public:
 static System::UInt32 Exchange(System::UInt32 % location1, System::UInt32 value);

[System.CLSCompliant(false)]
public static uint Exchange (ref uint location1, uint value);

[<System.CLSCompliant(false)>]
static member Exchange : uint32 * uint32 -> uint32

Public Shared Function Exchange (ByRef location1 As UInteger, value As UInteger) As UInteger

Parameters

location1

UInt32

The variable to set to the specified value.

value

UInt32

The value to which the location1 parameter is set.

Returns

UInt32

The original value of location1.

Attributes

CLSCompliantAttribute

Exceptions

NullReferenceException

The address of location1 is a null pointer.

Exchange(Single, Single)

Source:

Interlocked.cs

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 -> single

Public Shared Function Exchange (ByRef location1 As Single, value As Single) As Single

Parameters

location1

Single

The variable to set to the specified value.

value

Single

The value to which the location1 parameter is set.

Returns

Single

The original value of location1.

Exceptions

NullReferenceException

The address of location1 is a null pointer.

See also

• Managed Threading
• Overview of synchronization primitives

Exchange(UIntPtr, UIntPtr)

Source:

Interlocked.cs

Important

This API is not CLS-compliant.

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

public:
 static UIntPtr Exchange(UIntPtr % location1, UIntPtr value);

[System.CLSCompliant(false)]
public static UIntPtr Exchange (ref UIntPtr location1, UIntPtr value);

[<System.CLSCompliant(false)>]
static member Exchange : unativeint * unativeint -> unativeint

Public Shared Function Exchange (ByRef location1 As UIntPtr, value As UIntPtr) As UIntPtr

Parameters

location1

UIntPtr

unativeint

The variable to set to the specified value.

value

UIntPtr

unativeint

The value to which the location1 parameter is set.

Returns

UIntPtr

unativeint

The original value of location1.

Attributes

CLSCompliantAttribute

Exceptions

NullReferenceException

The address of location1 is a null pointer.

Exchange(UInt64, UInt64)

Source:

Interlocked.cs

Important

This API is not CLS-compliant.

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

public:
 static System::UInt64 Exchange(System::UInt64 % location1, System::UInt64 value);

[System.CLSCompliant(false)]
public static ulong Exchange (ref ulong location1, ulong value);

[<System.CLSCompliant(false)>]
static member Exchange : uint64 * uint64 -> uint64

Public Shared Function Exchange (ByRef location1 As ULong, value As ULong) As ULong

Parameters

location1

UInt64

The variable to set to the specified value.

value

UInt64

The value to which the location1 parameter is set.

Returns

UInt64

The original value of location1.

Attributes

CLSCompliantAttribute

Exceptions

NullReferenceException

The address of location1 is a null pointer.

Exchange(IntPtr, IntPtr)

Source:

Interlocked.cs

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 -> nativeint

Public Shared Function Exchange (ByRef location1 As IntPtr, value As IntPtr) As IntPtr

Parameters

location1

IntPtr

nativeint

The variable to set to the specified value.

value

IntPtr

nativeint

The value to which the location1 parameter is set.

Returns

IntPtr

nativeint

The original value of location1.

Exceptions

NullReferenceException

The address of location1 is a null pointer.

See also

• Managed Threading
• Overview of synchronization primitives

Exchange(Int64, Int64)

Source:

Interlocked.cs

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 -> int64

Public Shared Function Exchange (ByRef location1 As Long, value As Long) As Long

Parameters

location1

Int64

The variable to set to the specified value.

value

Int64

The value to which the location1 parameter is set.

Returns

Int64

The original value of location1.

Exceptions

NullReferenceException

The address of location1 is a null pointer.

See also

• Managed Threading
• Overview of synchronization primitives

Exchange(Int32, Int32)

Source:

Interlocked.cs

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 -> int

Public Shared Function Exchange (ByRef location1 As Integer, value As Integer) As Integer

Parameters

location1

Int32

The variable to set to the specified value.

value

Int32

The value to which the location1 parameter is set.

Returns

Int32

The original value of location1.

Exceptions

ArgumentNullException

The address of location1 is a null pointer.

NullReferenceException

The address of location1 is a null pointer.

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.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

        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

See also

• Managed Threading
• Overview of synchronization primitives

Exchange(Double, Double)

Source:

Interlocked.cs

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 -> double

Public Shared Function Exchange (ByRef location1 As Double, value As Double) As Double

Parameters

location1

Double

The variable to set to the specified value.

value

Double

The value to which the location1 parameter is set.

Returns

Double

The original value of location1.

Exceptions

NullReferenceException

The address of location1 is a null pointer.

See also

• Managed Threading
• Overview of synchronization primitives

Exchange(Object, Object)

Source:

Interlocked.cs

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 -> obj

Public Shared Function Exchange (ByRef location1 As Object, value As Object) As Object

Parameters

location1

Object

The variable to set to the specified value.

value

Object

The value to which the location1 parameter is set.

Returns

Object

The original value of location1.

Exceptions

ArgumentNullException

The address of location1 is a null pointer.

NullReferenceException

The address of location1 is a null pointer.

Remarks

Important

Beginning with .NET Framework 2.0, the Exchange<T>(T, T) method overload provides a type-safe alternative for reference types. We recommend that you call it instead of this overload.

See also

• Managed Threading
• Overview of synchronization primitives

Exchange<T>(T, T)

Source:

Interlocked.CoreCLR.cs

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);

public static T Exchange<T> (ref T location1, T value) where T : class;

static member Exchange : 'T * '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

T

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

value

T

The value to which the location1 parameter is set.

Returns

T

The original value of location1.

Exceptions

NullReferenceException

The address of location1 is a null pointer.

NotSupportedException

An unsupported T is specified.

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 .