Interlocked::Decrement Method (Int32%)
Decrements a specified variable and stores the result, as an atomic operation.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- location
- Type: System::Int32%
The variable whose value is to be decremented.
| Exception | Condition |
|---|---|
| ArgumentNullException | The address of location is a null pointer. |
This method handles an overflow condition by wrapping: If location = Int32::MinValue, location - 1 = Int32::MaxValue. No exception is thrown.
The following code example shows a thread-safe way to increment and decrement an integer value. SafeInstanceCount will always be zero. However, UnsafeInstanceCount will not necessarily be zero because a race condition occurs between incrementing and decrementing the count. This effect is especially marked on a multiprocessor computer.
Note |
|---|
The C++ example does not follow the IDisposable::Dispose pattern. (See Destructors and Finalizers in Visual C++.) The finalizer is used to decrement the counters, so that garbage collection causes decrementing. |
using namespace System; using namespace System::Threading; ref class CountClass { private: static int unsafeInstanceCount; static int safeInstanceCount; public: static property int UnsafeInstanceCount { int get() { return unsafeInstanceCount; } } static property int SafeInstanceCount { int get() { return safeInstanceCount; } } CountClass() { unsafeInstanceCount++; Interlocked::Increment( safeInstanceCount ); } // Destructor and finalizer. The finalizer is used to decrement the // count, so garbage collection enforces decrementing. ~CountClass() { this->!CountClass(); } !CountClass() { unsafeInstanceCount--; Interlocked::Decrement( safeInstanceCount ); } }; ref class Test { public: static void ThreadMethod() { CountClass^ cClass; // Create 100,000 instances of CountClass. for ( int i = 0; i < 100000; i++ ) { cClass = gcnew CountClass; } } }; int main() { Thread^ thread1 = gcnew Thread( gcnew ThreadStart( &Test::ThreadMethod ) ); Thread^ thread2 = gcnew Thread( gcnew ThreadStart( &Test::ThreadMethod ) ); thread1->Start(); thread2->Start(); thread1->Join(); thread2->Join(); // Have the garbage collector run the finalizer for each // instance of CountClass and wait for it to finish. GC::Collect(); GC::WaitForPendingFinalizers(); Console::WriteLine( "UnsafeInstanceCount: {0}" "\nSafeCountInstances: {1}", CountClass::UnsafeInstanceCount.ToString(), CountClass::SafeInstanceCount.ToString() ); }
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Note