Understanding The COM Single-Threaded Apartment Part 1

#define _WIN32_WINNT 0x0400
#include <windows.h>
#include <stdio.h>

#import "..\..\..\..\SimpleCOMObject2\Debug\SimpleCOMObject2.dll"
using namespace SIMPLECOMOBJECT2Lib;





// Simple function that displays the current thread ID.
void DisplayCurrentThreadId()
{
  TCHAR szMessage[256];

  sprintf (szMessage, "Thread ID : 0x%X", GetCurrentThreadId());

  ::MessageBox(NULL, szMessage, "TestMethod1()", MB_OK);
}





DWORD WINAPI ThreadFunc(LPVOID lpvParameter)
{
  ::CoInitializeEx(NULL, COINIT_MULTITHREADED);

  DisplayCurrentThreadId();

  if (1)
  {
    ISimpleCOMObject2Ptr spISimpleCOMObject2A;
	ISimpleCOMObject2Ptr spISimpleCOMObject2B;

    spISimpleCOMObject2A.CreateInstance(__uuidof(SimpleCOMObject2));
	spISimpleCOMObject2B.CreateInstance(__uuidof(SimpleCOMObject2));

	spISimpleCOMObject2A -> TestMethod1();
	spISimpleCOMObject2B -> TestMethod1();
  }

  ::CoUninitialize();

  return 0;
}





int main()
{
  HANDLE hThread = NULL;
  DWORD  dwThreadId = 0;

  ::CoInitializeEx(NULL, COINIT_MULTITHREADED);

  DisplayCurrentThreadId();

  if (1)
  {
    ISimpleCOMObject2Ptr spISimpleCOMObject2;

    spISimpleCOMObject2.CreateInstance(__uuidof(SimpleCOMObject2));

    spISimpleCOMObject2 -> TestMethod1();

    hThread = CreateThread
    (
      (LPSECURITY_ATTRIBUTES)NULL, // SD
      (SIZE_T)0,                       // initial stack size
      (LPTHREAD_START_ROUTINE)ThreadFunc,    // thread function
      (LPVOID)NULL,                       // thread argument
      (DWORD)0,                    // creation option
      (LPDWORD)&dwThreadId                        // thread identifier
    );

    WaitForSingleObject(hThread, INFINITE);

	spISimpleCOMObject2 -> TestMethod1();
  }

  ::CoUninitialize();

  return 0;
}