STA in COM

STA in COM

COM now has five types of Apartment:
1. Legacy
2. STA
3. Free
4. Both
5. Neutral

I'll discuss the Apartment in this article.

COM Objects living in Apartment will be protected by COM, any other calls for this object will be serialized by the COM. If there are concurrent threading in your application and you also don't want to the complicated multi-thread concurrency, you may get to love the Apartment model.

Here are some points of the Apartment modle:
1. Each Single Apartment only contains one thread.
2. Each thread should call ::CoInitializeEx(NULL, COINIT_APARTMENTTHREADED); to join the STA.
3. If  you want to call the STA COM object living in other STA, you need to marshal your pointer.
4. Each STA may contain more than one COM objects.
5. At one time a STA allows only one thread running.

The code for COM object is simple. Here is I just list the code snippet for the client.

#include  < iostream >
using   namespace  std;

#import  " CarDemo.dll "  no_namespace



void  ThreadFunc( void   * );
// IFreeCar * pCar;
// IFreeCar * pCar;
ICar  *  pCar;
int  _tmain( int  argc, _TCHAR *  argv[])
{
    ::CoInitializeEx(NULL, COINIT_MULTITHREADED);
    {
        ICar  *  pCar;
        ::CoCreateInstance(__uuidof(Car) , NULL, CLSCTX_INPROC_SERVER  , __uuidof(ICar) , ( void ** ) & pCar);
        IStream *  interfaceStream1;
        IStream *  interfaceStream2;
        CoMarshalInterThreadInterfaceInStream(__uuidof(ICar), pCar,  & interfaceStream1);
        CoMarshalInterThreadInterfaceInStream(__uuidof(ICar), pCar,  & interfaceStream2);
        HANDLE hThread[ 2 ];
        hThread[ 0 ]  =  (HANDLE)::_beginthread(ThreadFunc,  0 , ( void * )interfaceStream1);
        hThread[ 1 ]  =  (HANDLE)::_beginthread(ThreadFunc,  0 , ( void * )interfaceStream2);
        ::WaitForMultipleObjects( 2 , hThread,  true , INFINITE);

        pCar -> Release();

    }
     int  iVal;
    cin >> iVal;

    ::CoUninitialize();
     return   0 ;
}

void  ThreadFunc(LPVOID lpParameter)
{
    ::CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
    {
        IStream *  pStream  =  reinterpret_cast < IStream *> (lpParameter);
        ICar  *  pCar;
        CoGetInterfaceAndReleaseStream(pStream, __uuidof(ICar), reinterpret_cast < void **> ( & pCar));
        pCar -> Drive( 3 );
        pCar -> Release();
    }
    ::CoUninitialize();
}

Here is some helpful links for you to understand the STA better:
http://support.microsoft.com/default.aspx?scid=kb;en-us;172314
http://support.microsoft.com/kb/206076