PRB: COM Objects are not Being Released in Java (179062)

The information in this article applies to:

Microsoft SDK for Java 1.51
Microsoft SDK for Java 2.0
Microsoft SDK for Java 2.01
Microsoft SDK for Java 2.02
Microsoft SDK for Java 3.0
Microsoft SDK for Java 3.1
Microsoft SDK for Java 3.2
Microsoft Visual J++ 1.0
Microsoft Visual J++ 1.1

This article was previously published under Q179062

SYMPTOMS

When setting a COM object reference to null and possibly attempting to force garbage collection by calling gc(), COM objects may not be released in a timely or predictable fashion.

CAUSE

If you do not call ComLib.release, normal garbage-collection will attempt to perform the release for you. However, this mechanism is not guaranteed due to the threading limitations of many COM objects. That is, many COM objects can be called only on the thread on which they were created. Because garbage collection occurs at unpredictable times, the required thread may have expired or may be no longer responding to messages by the time garbage-collection reclaims the object. In addition, this unpredictability can obscure true memory leaks and/or tie up important system resources.

RESOLUTION

It is recommended that you use explicit releases by calling ComLib.release in order to free COM objects in a timely and predictable fashion.

MORE INFORMATION

For example, if you have the following code that creates a COM object in Java:

import excel8.*;
import com.ms.com.*;

_Global globXL=null;
_Application appXL=null;

try
{
   globXL = (_Global)new Global();
   appXL = (_Application)globXL.getApplication();
}
catch (ComFailException e)
{
   System.out.println(e.getMessage());
}

You would use this to release these COM objects (note all references to COM objects should be released):

try
{
   ComLib.release(appXL);
   appXL=null;
   ComLib.release(globXL);
   globXL=null;
}
catch (ComFailException e)
{
   System.out.println(e.getMessage());
}

REFERENCES

For more information (available in the Microsoft SDK for Java documentation), visit the following Microsoft Web site:

http://www.microsoft.com/mscorp/java/

For support information about Visual J++ and the SDK for Java, visit the following Microsoft Web site:

http://www.microsoft.com/java

Modification Type:	Major	Last Reviewed:	6/14/2006
Keywords:	kbprb KB179062