William Ferrell
f5a5e9653b
Passed *every* piece of source in this project through indent. I'm setting things up with ctags soon and am actually going to *gasp* use a nice programming environment to continue development in. :)
158 lines
3.2 KiB
C
158 lines
3.2 KiB
C
/*
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* lcd_sem.c -- semaphore code written for lcdtime and meter to mediate
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* access to the parallel port.
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*
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* Written by Benjamin Tse (blt@mundil.cs.mu.edu.au); August,October 1995
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*
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* Functions in this file:
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* getkey returns the key for the semaphore
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* sem_get create the semaphore (and initialise) if one doesn't exist
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* otherwise return its key
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* sem_wait wait on the semaphore
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* sem_signal signal on the semaphore
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* sem_remove remove the semaphore
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*
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* Legal stuff: At no stage was this program written, assembled or compiled on
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* any computer at the University of Melbourne, Australia. This program is
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* Copyright (C) 1995 Benjamin Tse (blt@mundil.cs.mu.oz.au) and covered by
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* GNU's GPL. In particular, this program is free software and comes WITHOUT
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* ANY WARRANTY.
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*
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* $Id$
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h> /* for semaphore functions */
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#include <sys/ipc.h>
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#include <sys/sem.h>
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#include <errno.h>
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#include "lcd_sem.h"
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#define SEMAPHORE "portctrl"
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#define SEMKEY 0x706f7274 /* semaphore key */
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#define SEMCOUNT 1 /* number of semaphores to create */
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#define WMODE 0660 /* access permissions */
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#define SEM_SIGNAL 0,1,SEM_UNDO
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#define SEM_WAIT 0,-1,SEM_UNDO
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/* functions local to this file */
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static key_t getkey (register char *p);
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/* global variables */
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static struct sembuf semaphore_wait = { SEM_WAIT };
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static struct sembuf semaphore_signal = { SEM_SIGNAL };
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static char rcsId[] = "$Id$";
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/*
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* getkey returns the key for the semaphore
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*/
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static key_t
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getkey (register char *p)
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{
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return ((key_t) SEMKEY);
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}
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/*
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* create the semaphore if one doesn't exist and initialise it to 1, else
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* return the semaphore set id
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*/
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int
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sem_get (void)
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{
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int semid;
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union semun semval;
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if ((semid = semget (getkey (SEMAPHORE), SEMCOUNT, IPC_CREAT | IPC_EXCL | WMODE)) < 0) {
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switch (errno) {
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case EEXIST:
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/* semaphore set exists, get id and return it */
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if ((semid = semget (getkey (SEMAPHORE), SEMCOUNT, IPC_EXCL | WMODE)) < 0) {
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perror ("semget");
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exit (1);
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}
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return semid;
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break;
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case EACCES:
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/* don't have permissions for semaphore, need to change key */
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perror ("semget, can't get permissions for semaphore");
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exit (1);
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break;
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default:
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perror ("semget");
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exit (1);
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break;
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}
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} else {
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/* initialise semaphore to 1 */
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semval.val = 1;
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if (semctl (semid, 0, SETVAL, semval) < 0) {
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perror ("setval, can't initialise semaphore");
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exit (1);
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}
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}
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return semid;
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}
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/*
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* wait on the semaphore
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*/
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int
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sem_wait (int sid)
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{
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if (semop (sid, &semaphore_wait, 1) < -1) {
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perror (SEMAPHORE);
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exit (1);
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}
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return 0;
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}
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/*
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* signal on the semaphore
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*/
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int
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sem_signal (int sid)
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{
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if (semop (sid, &semaphore_signal, 1) < -1) {
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perror (SEMAPHORE);
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exit (1);
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}
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return 0;
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}
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/*
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* remove the semaphore
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*/
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int
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sem_remove (int sid)
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{
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int i;
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union semun dummy;
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if ((i = semctl (sid, 0, IPC_RMID, dummy)) < 0) {
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switch (i) {
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case EIDRM:
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/* semaphore removed */
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return 0;
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break;
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default:
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perror ("semctl, removing semaphore");
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exit (1);
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}
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}
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return 0;
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}
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