[mLib] / lock.c

/* -*-c-*-
 *
 * $Id: lock.c,v 1.2 1999/05/26 20:53:40 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 1.2  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;
  void (*alrm)(int);
  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));
  }

  /* --- Set an alarm handler --- */

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

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

/*----- That's all, fokls -------------------------------------------------*/
Commit	Line	Data
edb89af3	1	/* --c--
edb89af3	2	*
898dd094	3	* $Id: lock.c,v 1.2 1999/05/26 20:53:40 mdw Exp $
edb89af3	4	*
	5	* Simplified POSIX locking interface
	6	*
	7	* (c) 1997 Straylight/Edgeware
	8	*/
	9
	10	/----- Licensing notice --------------------------------------------------
	11	*
	12	* This file is part of the mLib utilities library.
	13	*
	14	* mLib is free software; you can redistribute it and/or modify
	15	* it under the terms of the GNU Library General Public License as
	16	* published by the Free Software Foundation; either version 2 of the
	17	* License, or (at your option) any later version.
	18	*
	19	* mLib is distributed in the hope that it will be useful,
	20	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	21	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	22	* GNU Library General Public License for more details.
	23	*
	24	* You should have received a copy of the GNU Library General Public
	25	* License along with mLib; if not, write to the Free
	26	* Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
	27	* MA 02111-1307, USA.
	28	*/
	29
	30	/----- Revision history --------------------------------------------------
	31	*
	32	* $Log: lock.c,v $
898dd094	33	* Revision 1.2 1999/05/26 20:53:40 mdw
	34	* Fixes for stupid bugs.
	35	*
edb89af3	36	* Revision 1.1 1999/05/15 10:33:53 mdw
	37	* Add simplified locking code.
	38	*
	39	*/
	40
	41	/----- Header files ------------------------------------------------------/
	42
	43	#include <errno.h>
	44	#include <signal.h>
	45	#include <stdio.h>
	46	#include <stdlib.h>
	47	#include <string.h>
	48	#include <time.h>
	49
	50	#include <sys/types.h>
	51	#include <unistd.h>
	52	#include <fcntl.h>
	53
	54	#include "lock.h"
	55
	56	/----- Tunable constants -------------------------------------------------/
	57
	58	#define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */
	59
	60	/----- Main code ---------------------------------------------------------/
	61
	62	/* --- @lock_alarm@ --- *
	63	*
	64	* Arguments: @int sig@ = signal number
	65	*
	66	* Returns: ---
	67	*
	68	* Use: Makes sure that a @SIGALRM@ signal interrupts system calls.
	69	*/
	70
	71	static void lock_alarm(int sig) { ; }
	72
	73	/* --- @lock_file@ --- *
	74	*
	75	* Arguments: @int fd@ = file descriptor to lock
	76	* @unsigned how@ = type of lock required
	77	*
	78	* Returns: 0 if OK, -1 if it failed.
	79	*
	80	* Use: Acquires a lock on the given file. The value @how@
	81	* specifies the type of lock to acquire: @LOCK_EXCL@ gets
	82	* an exclusive (write) lock; @LOCK_NONEXCL@ gets a non-
	83	* exclusive (read) lock and @LOCK_UNLOCK@ releases any locks.
	84	* Acquiring a lock gets timed out after a while with an
	85	* error.
	86	*/
	87
	88	int lock_file(int fd, unsigned how)
	89	{
	90	struct flock fk;
	91	void (*alrm)(int);
	92	int e;
	93
	94	/* --- Fill in the easy bits --- */
	95
	96	fk.l_whence = SEEK_SET;
	97	fk.l_start = 0;
898dd094	98	fk.l_len = 0;
edb89af3	99
	100	/* --- Unlocking is really easy --- */
	101
	102	if (how == LOCK_UNLOCK) {
	103	fk.l_type = F_UNLCK;
	104	return (fcntl(fd, F_SETLK, &fk));
	105	}
	106
	107	/* --- Set an alarm handler --- */
	108
	109	if (how == LOCK_EXCL)
	110	fk.l_type = F_WRLCK;
	111	else if (how == LOCK_NONEXCL)
	112	fk.l_type = F_RDLCK;
	113	else {
	114	errno = EINVAL;
	115	return (-1);
	116	}
	117
	118	alrm = signal(SIGALRM, lock_alarm);
	119	alarm(LOCK_TIMEOUT);
	120	if ((e = fcntl(fd, F_SETLKW, &fk)) != 0) {
	121	if (errno == EINTR)
	122	errno = EAGAIN;
	123	}
898dd094	124	alarm(0);
edb89af3	125	signal(SIGALRM, alrm);
	126	return (e);
	127	}
	128
	129	/----- That's all, fokls -------------------------------------------------/