[mLib] / lock.c

/* -*-c-*-
 *
 * $Id: lock.c,v 1.1 1999/05/15 10:33:53 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 1.1  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_whence = 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;
  }
  signal(SIGALRM, alrm);
  return (e);
}

/*----- That's all, fokls -------------------------------------------------*/
Commit	Line	Data
edb89af3	1	/* --c--
	2	*
	3	* $Id: lock.c,v 1.1 1999/05/15 10:33:53 mdw Exp $
	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 $
	33	* Revision 1.1 1999/05/15 10:33:53 mdw
	34	* Add simplified locking code.
	35	*
	36	*/
	37
	38	/----- Header files ------------------------------------------------------/
	39
	40	#include <errno.h>
	41	#include <signal.h>
	42	#include <stdio.h>
	43	#include <stdlib.h>
	44	#include <string.h>
	45	#include <time.h>
	46
	47	#include <sys/types.h>
	48	#include <unistd.h>
	49	#include <fcntl.h>
	50
	51	#include "lock.h"
	52
	53	/----- Tunable constants -------------------------------------------------/
	54
	55	#define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */
	56
	57	/----- Main code ---------------------------------------------------------/
	58
	59	/* --- @lock_alarm@ --- *
	60	*
	61	* Arguments: @int sig@ = signal number
	62	*
	63	* Returns: ---
	64	*
65	* Use: Makes sure that a @SIGALRM@ signal interrupts system calls.
66	*/
67
68	static void lock_alarm(int sig) { ; }
69
70	/* --- @lock_file@ --- *
71	*
72	* Arguments: @int fd@ = file descriptor to lock
73	* @unsigned how@ = type of lock required
74	*
75	* Returns: 0 if OK, -1 if it failed.
76	*
77	* Use: Acquires a lock on the given file. The value @how@
78	* specifies the type of lock to acquire: @LOCK_EXCL@ gets
79	* an exclusive (write) lock; @LOCK_NONEXCL@ gets a non-
80	* exclusive (read) lock and @LOCK_UNLOCK@ releases any locks.
81	* Acquiring a lock gets timed out after a while with an
82	* error.
83	*/
84
85	int lock_file(int fd, unsigned how)
86	{
87	struct flock fk;
88	void (*alrm)(int);
89	int e;
90
91	/* --- Fill in the easy bits --- */
92
93	fk.l_whence = SEEK_SET;
94	fk.l_start = 0;
95	fk.l_whence = 0;
96
97	/* --- Unlocking is really easy --- */
98
99	if (how == LOCK_UNLOCK) {
100	fk.l_type = F_UNLCK;
101	return (fcntl(fd, F_SETLK, &fk));
102	}
103
104	/* --- Set an alarm handler --- */
105
106	if (how == LOCK_EXCL)
107	fk.l_type = F_WRLCK;
108	else if (how == LOCK_NONEXCL)
109	fk.l_type = F_RDLCK;
110	else {
111	errno = EINVAL;
112	return (-1);
113	}
114
115	alrm = signal(SIGALRM, lock_alarm);
116	alarm(LOCK_TIMEOUT);
117	if ((e = fcntl(fd, F_SETLKW, &fk)) != 0) {
118	if (errno == EINTR)
119	errno = EAGAIN;
120	}
121	signal(SIGALRM, alrm);
122	return (e);
123	}
124
125	/----- That's all, fokls -------------------------------------------------/