WinThreadAssocQueue associates the thread of a debug application with, or disassociates it from, the message queue of the program that is being debugged.

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

HAB     hab;      /*  Anchor-block handle. */
HMQ     hmq;      /*  Message-queue handle. */
BOOL    Success;  /*  Success indicator. */

Success = WinThreadAssocQueue(hab, hmq);