DosReleaseRamSem releases a RAM semaphore. This is used at the exit from a range of code which must not be executed simultaneously in multiple threads.

#define INCL_DOSSEMAPHORES
#include <os2.h>

PRAMSEM    pramsem;  /*  Pointer to the RAM semaphore structure. */
ULONG      flag;     /*  Release flag. */
APIRET     rc;       /*  Return code. */

rc = DosReleaseRamSem(pramsem, flag);