3 * $Id: lock.c,v 1.1 1999/05/15 10:33:53 mdw Exp $
5 * Simplified POSIX locking interface
7 * (c) 1997 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of the mLib utilities library.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.1 1999/05/15 10:33:53 mdw
34 * Add simplified locking code.
38 /*----- Header files ------------------------------------------------------*/
47 #include <sys/types.h>
53 /*----- Tunable constants -------------------------------------------------*/
55 #define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */
57 /*----- Main code ---------------------------------------------------------*/
59 /* --- @lock_alarm@ --- *
61 * Arguments: @int sig@ = signal number
65 * Use: Makes sure that a @SIGALRM@ signal interrupts system calls.
68 static void lock_alarm(int sig) { ; }
70 /* --- @lock_file@ --- *
72 * Arguments: @int fd@ = file descriptor to lock
73 * @unsigned how@ = type of lock required
75 * Returns: 0 if OK, -1 if it failed.
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
85 int lock_file(int fd, unsigned how)
91 /* --- Fill in the easy bits --- */
93 fk.l_whence = SEEK_SET;
97 /* --- Unlocking is really easy --- */
99 if (how == LOCK_UNLOCK) {
101 return (fcntl(fd, F_SETLK, &fk));
104 /* --- Set an alarm handler --- */
106 if (how == LOCK_EXCL)
108 else if (how == LOCK_NONEXCL)
115 alrm = signal(SIGALRM, lock_alarm);
117 if ((e = fcntl(fd, F_SETLKW, &fk)) != 0) {
121 signal(SIGALRM, alrm);
125 /*----- That's all, fokls -------------------------------------------------*/