3 * $Id: lock.c,v 1.3 1999/06/06 01:23:00 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 1.3 1999/06/06 01:23:00 mdw
34 * Fix signal handling.
36 * Revision 1.2 1999/05/26 20:53:40 mdw
37 * Fixes for stupid bugs.
39 * Revision 1.1 1999/05/15 10:33:53 mdw
40 * Add simplified locking code.
44 /*----- Header files ------------------------------------------------------*/
53 #include <sys/types.h>
59 /*----- Tunable constants -------------------------------------------------*/
61 #define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */
63 /*----- Main code ---------------------------------------------------------*/
65 /* --- @lock_alarm@ --- *
67 * Arguments: @int sig@ = signal number
71 * Use: Makes sure that a @SIGALRM@ signal interrupts system calls.
74 static void lock_alarm(int sig) { ; }
76 /* --- @lock_file@ --- *
78 * Arguments: @int fd@ = file descriptor to lock
79 * @unsigned how@ = type of lock required
81 * Returns: 0 if OK, -1 if it failed.
83 * Use: Acquires a lock on the given file. The value @how@
84 * specifies the type of lock to acquire: @LOCK_EXCL@ gets
85 * an exclusive (write) lock; @LOCK_NONEXCL@ gets a non-
86 * exclusive (read) lock and @LOCK_UNLOCK@ releases any locks.
87 * Acquiring a lock gets timed out after a while with an
91 int lock_file(int fd, unsigned how)
94 struct sigaction sa, oldsa;
97 /* --- Fill in the easy bits --- */
99 fk.l_whence = SEEK_SET;
103 /* --- Unlocking is really easy --- */
105 if (how == LOCK_UNLOCK) {
107 return (fcntl(fd, F_SETLK, &fk));
110 /* --- Decide how to do the locking --- */
112 if (how == LOCK_EXCL)
114 else if (how == LOCK_NONEXCL)
121 /* --- Set up the alarm --- */
123 sa.sa_handler = lock_alarm;
125 sigemptyset(&sa.sa_mask);
126 if (sigaction(SIGALRM, &sa, &oldsa))
132 if ((e = fcntl(fd, F_SETLKW, &fk)) != 0) {
137 /* --- Remove the alarm handling --- */
140 sigaction(SIGALRM, &oldsa, 0);
144 /*----- That's all, fokls -------------------------------------------------*/