Interlocked.CompareExchange メソッド
2 つの値が等しいかどうかを比較します。等しい場合は、それらの値のいずれかを置き換えます。
オーバーロードの一覧
2 つの 32 ビット符号付き整数が等しいかどうかを比較します。等しい場合は、それらの値のいずれかを置き換えます。
.NET Compact Framework でもサポート。
[Visual Basic] Overloads Public Shared Function CompareExchange(ByRef Integer, Integer, Integer) As Integer
[JScript] public static function CompareExchange(int, int, int) : int;
2 つのオブジェクトが等しいかどうかを比較します。等しい場合は、オブジェクトのいずれかを置き換えます。
.NET Compact Framework でもサポート。
[Visual Basic] Overloads Public Shared Function CompareExchange(ByRef Object, Object, Object) As Object
[C#] public static object CompareExchange(ref object, object, object);
[C++] public: static Object* CompareExchange(Object**, Object**, Object**);
[JScript] public static function CompareExchange(Object, Object, Object) : Object;
2 つの単精度浮動小数点数が等しいかどうかを比較します。等しい場合は、それらの値のいずれかを置き換えます。
[Visual Basic] Overloads Public Shared Function CompareExchange(ByRef Single, Single, Single) As Single
[C#] public static float CompareExchange(ref float, float, float);
[C++] public: static float CompareExchange(float*, float*, float*);
[JScript] public static function CompareExchange(float, float, float) : float;
使用例
[Visual Basic, C#, C++] メモ ここでは、CompareExchange のオーバーロード形式のうちの 1 つだけについて、使用例を示します。その他の例については、各オーバーロード形式のトピックを参照してください。
' 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
[C#]
// 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;
}
}
[C++]
// 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 <mscorlib.dll>
#using <system.dll>
using namespace System::Threading;
public __gc class ThreadSafe
{
// totalValue contains a running total that can be updated
// by multiple threads. It must be protected from unsynchronized
// access.
private:
int totalValue;
// The Total property returns the running total.
public:
__property int get_Total()
{
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(&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;
}
};
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