Fix signal handling.

[mLib] / lock.c

/* -*-c-*-
 *
 * $Id: lock.c,v 1.3 1999/06/06 01:23:00 mdw Exp $
 *
 * Simplified POSIX locking interface
 *
 * (c) 1997 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * mLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with mLib; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------*
 *
 * $Log: lock.c,v $
 * Revision 1.3  1999/06/06 01:23:00  mdw
 * Fix signal handling.
 *
 * Revision 1.2  1999/05/26 20:53:40  mdw
 * Fixes for stupid bugs.
 *
 * Revision 1.1  1999/05/15 10:33:53  mdw
 * Add simplified locking code.
 *
 */

/*----- Header files ------------------------------------------------------*/

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

#include "lock.h"

/*----- Tunable constants -------------------------------------------------*/

#define LOCK_TIMEOUT 10			/* Maximum time in seconds to wait */

/*----- Main code ---------------------------------------------------------*/

/* --- @lock_alarm@ --- *
 *
 * Arguments:	@int sig@ = signal number
 *
 * Returns:	---
 *
 * Use:		Makes sure that a @SIGALRM@ signal interrupts system calls.
 */

static void lock_alarm(int sig) { ; }

/* --- @lock_file@ --- *
 *
 * Arguments:	@int fd@ = file descriptor to lock
 *		@unsigned how@ = type of lock required
 *
 * Returns:	0 if OK, -1 if it failed.
 *
 * Use:		Acquires a lock on the given file.  The value @how@
 *		specifies the type of lock to acquire: @LOCK_EXCL@ gets
 *		an exclusive (write) lock; @LOCK_NONEXCL@ gets a non-
 *		exclusive (read) lock and @LOCK_UNLOCK@ releases any locks.
 *		Acquiring a lock gets timed out after a while with an
 *		error.
 */

int lock_file(int fd, unsigned how)
{
  struct flock fk;
  struct sigaction sa, oldsa;
  int e;

  /* --- Fill in the easy bits --- */

  fk.l_whence = SEEK_SET;
  fk.l_start = 0;
  fk.l_len = 0;

  /* --- Unlocking is really easy --- */

  if (how == LOCK_UNLOCK) {
    fk.l_type = F_UNLCK;
    return (fcntl(fd, F_SETLK, &fk));
  }

  /* --- Decide how to do the locking --- */

  if (how == LOCK_EXCL)
    fk.l_type = F_WRLCK;
  else if (how == LOCK_NONEXCL)
    fk.l_type = F_RDLCK;
  else {
    errno = EINVAL;
    return (-1);
  }

  /* --- Set up the alarm --- */

  sa.sa_handler = lock_alarm;
  sa.sa_flags = 0;
  sigemptyset(&sa.sa_mask);
  if (sigaction(SIGALRM, &sa, &oldsa))
    return (-1);

  /* --- Do it --- */

  alarm(LOCK_TIMEOUT);
  if ((e = fcntl(fd, F_SETLKW, &fk)) != 0) {
    if (errno == EINTR)
      errno = EAGAIN;
  }

  /* --- Remove the alarm handling --- */

  alarm(0);
  sigaction(SIGALRM, &oldsa, 0);
  return (e);
}

/*----- That's all, fokls -------------------------------------------------*/