This documentation is archived and is not being maintained.

Marshal.ReleaseComObject Method

Decrements the reference count of the supplied runtime callable wrapper.

[Visual Basic]
Public Shared Function ReleaseComObject( _
   ByVal o As Object _
) As Integer
public static int ReleaseComObject(
 object o
public: static int ReleaseComObject(
 Object* o
public static function ReleaseComObject(
   o : Object
) : int;


The COM object to release.

Return Value

The new value of the reference count of the runtime callable wrapper associated with o. This value is typically zero since the runtime callable wrapper keeps just one reference to the wrapped COM object regardless of the number of managed clients calling it.


Exception Type Condition
InvalidCastException o is not a valid COM object.
NullReferenceException o is a null reference (Nothing in Visual Basic).


Every time a COM interface pointer enters the common language runtime, it is wrapped in an runtime callable wrapper. If you are unfamiliar with the features of this wrapper, see Runtime Callable Wrapper.

This method is used to explicitly control the lifetime of a COM object used from managed code. You should use this method to free the underlying COM object that holds references to resources in a timely manner or when objects must be freed in a specific order.

The runtime callable wrapper has a reference count that is incremented every time a COM interface pointer is mapped to it. The ReleaseComObject method decrements the reference count of a runtime callable wrapper. When the reference count reached zero, the runtime releases all its references on the unmanaged COM object, and throws a System.NullReferenceException if you attempt to use the object further. If the same COM interface is passed more than once from unmanaged to managed code, the reference count on the wrapper is incremented every time and calling ReleaseComObject returns the number of remaining references.

Note   To ensure that the runtime callable wrapper and the original COM object are released, construct a loop from which you call this method until the returned reference count reaches zero.
Note   This method uses SecurityAction.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.


Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

.NET Framework Security: 

See Also

Marshal Class | Marshal Members | System.Runtime.InteropServices Namespace | NullReferenceException