This function destroys the message queue.

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

HMQ     hmq;  /*  Message-queue handle. */
BOOL    rc;   /*  Queue-destroyed indicator. */

rc = WinDestroyMsgQueue(hmq);