This function returns a code indicating the status of the message queue associated with the caller.

#define INCL_WINMESSAGEMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND     hwndDesktop;  /*  Desktop-window handle. */
ULONG    flStatus;     /*  Status information. */

flStatus = WinQueryQueueStatus(hwndDesktop);