This example shows how to create, open, query, request, release, and close a Mutual exclusion (Mutex) semaphore.

#define INCL_DOSSEMAPHORES      /* Semaphore values */
#define INCL_DOSERRORS          /* DOS Error values */
#include <os2.h>
#include <stdio.h>

int main(VOID) {
HMTX    hmtx     = NULLHANDLE; /* Mutex semaphore handle */
PID     pidOwner = 0;          /* PID of current mutex semaphore owner */
TID     tidOwner = 0;          /* TID of current mutex semaphore owner */
ULONG   ulCount  = 0;          /* Request count for the semaphore */
APIRET  rc       = NO_ERROR;   /* Return code */

   rc = DosCreateMutexSem("\\SEM32\\MUTEX1",      /* Semaphore name */
                          &hmtx, 0, FALSE);       /* Handle returned */
   if (rc != NO_ERROR) {
      printf("DosOpenMutexSem error: return code = %u\n", rc);
      return 1;
    }
        /* This would normally be done by another unit of work */
   rc = DosOpenMutexSem("\\SEM32\\MUTEX1",      /* Semaphore name */
                        &hmtx);                 /* Handle returned */
   if (rc != NO_ERROR) {
      printf("DosOpenMutexSem error: return code = %u\n", rc);
      return 1;
    }

   rc = DosRequestMutexSem(hmtx,                     /* Handle of semaphore */
                           (ULONG) SEM_INDEFINITE_WAIT);  /* Timeout (none) */
   if (rc != NO_ERROR) {
      printf("DosRequestMutexSem error: return code = %u\n", rc);
      return 1;
   }
   rc = DosQueryMutexSem(hmtx,         /* Handle of semaphore */
                         &pidOwner,    /* Process ID of owner */
                         &tidOwner,    /* Thread ID of owner */
                         &ulCount);    /* Count */
   if (rc != NO_ERROR) {
      printf("DosQueryMutexSem error: return code = %u\n", rc);
      return 1;
   } else  {
      printf("Semaphore owned by PID %u, TID %u.", pidOwner, tidOwner);
      printf("  Request count is %u.\n", ulCount);
   } /* endif */

   rc = DosReleaseMutexSem(hmtx);        /* Relinquish ownership */
   if (rc != NO_ERROR) {
      printf("DosReleaseMutexSem error: return code = %u\n", rc);
      return 1;
    }

   rc = DosCloseMutexSem(hmtx);          /* Close mutex semaphore */
   if (rc != NO_ERROR) {
      printf("DosCloseMutexSem error: return code = %u\n", rc);
      return 1;
   }

return NO_ERROR;
}