Java threads blocking when accessing COM objects (232368)

SYMPTOMS

When using COM objects in a multi-threaded Java application, calls on apartment-threaded COM objects are serialized, even when the objects are created on their own threads. COM rules state that only one thread may exist in a Single Threaded Apartment (STA), and all calls to any object in that apartment must be serviced by the apartment's one and only thread.

This behavior, by design, serializes calls on objects in the apartment from other threads calling across apartment boundaries. However, in Java, even when apartment-model objects are created on their own Java threads and in what would seem to be their own individual STAs, calls on the objects from other threads are serialized and blocking may occur. In the Microsoft virtual machine, unless steps are taken to avoid the default behavior, calls on apartment-threaded objects are in fact being serviced by the same thread, regardless of the Java thread that created them.

package tutorial.sample;

public class STA extends Thread {
   /** 
    *Hosted COM object
    */ 
   private Object comObject = null;
   /**
    *   The returned object will be a proxy to the hosted COM object.
    *   The Microsoft VM will automatically take care of any thread
    *   marshaling requirements, allowing the returned object to be
    *   used like any other Java object.
    */ 
   public Object getHostedCOMObject( ){
      return com.ms.com.ComLib.makeProxyRef(comObject);
   }
   
   public void run(){
      com.ms.com.ComLib.declareMessagePumpThread();
      comObject = new SomeJCWClass();
      com.ms.win32.MSG msg = new com.ms.win32.MSG();
         while (com.ms.win32.User32.GetMessage(msg, 0, 0, 0)) {
            com.ms.win32.User32.TranslateMessage(msg);
              com.ms.win32.User32.DispatchMessage(msg);
      }
   }
}