This function obtains the process identity and thread identity of the thread that created a window.

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

HWND    hwnd;  /*  Window handle. */
PPID    ppid;  /*  Process identity of the thread that created the window. */
PTID    ptid;  /*  Thread identity of the thread that created the window. */
BOOL    rc;    /*  Success indicator. */

rc = WinQueryWindowProcess(hwnd, ppid, ptid);