3 * $Id: lock.c,v 1.5 1999/06/19 20:35:45 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 1.5 1999/06/19 20:35:45 mdw
34 * Whoops. I'd left the type of the jump buffer as `sigjmp_buf'.
36 * Revision 1.4 1999/06/19 20:33:16 mdw
37 * More sophisticated and excessive signal and alarm handling.
39 * Revision 1.3 1999/06/06 01:23:00 mdw
40 * Fix signal handling.
42 * Revision 1.2 1999/05/26 20:53:40 mdw
43 * Fixes for stupid bugs.
45 * Revision 1.1 1999/05/15 10:33:53 mdw
46 * Add simplified locking code.
50 /*----- Header files ------------------------------------------------------*/
60 #include <sys/types.h>
66 /*----- Tunable constants -------------------------------------------------*/
68 #define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */
70 /*----- Static variables --------------------------------------------------*/
72 static jmp_buf jmp; /* Jump here to interrup @fcntl@ */
74 /*----- Main code ---------------------------------------------------------*/
76 /* --- @sigalrm@ --- *
78 * Arguments: @int sig@ = signal number
82 * Use: Makes sure that a @SIGALRM@ signal interrupts system calls.
85 static void sigalrm(int sig) { longjmp(jmp, 1); }
87 /* --- @lock_file@ --- *
89 * Arguments: @int fd@ = file descriptor to lock
90 * @unsigned how@ = type of lock required
92 * Returns: 0 if OK, -1 if it failed.
94 * Use: Acquires a lock on the given file. The value @how@
95 * specifies the type of lock to acquire: @LOCK_EXCL@ gets
96 * an exclusive (write) lock; @LOCK_NONEXCL@ gets a non-
97 * exclusive (read) lock and @LOCK_UNLOCK@ releases any locks.
98 * Acquiring a lock gets timed out after a while with an
102 int lock_file(int fd, unsigned how)
105 struct sigaction sa, osa;
110 /* --- Fill in the easy bits --- */
112 fk.l_whence = SEEK_SET;
116 /* --- Unlocking is really easy --- */
118 if (how == LOCK_UNLOCK) {
120 return (fcntl(fd, F_SETLK, &fk));
123 /* --- Decide how to do the locking --- */
125 if (how == LOCK_EXCL)
127 else if (how == LOCK_NONEXCL)
134 /* --- Block @SIGALRM@ for a while --- *
136 * I don't want stray alarms going off while I'm busy here.
140 sigaddset(&ss, SIGALRM);
141 if (sigprocmask(SIG_BLOCK, &ss, &oss))
144 /* --- Set up the signal handler --- */
146 sa.sa_handler = sigalrm;
149 sa.sa_flags |= SA_INTERRUPT;
151 sigemptyset(&sa.sa_mask);
152 if (sigaction(SIGALRM, &sa, &osa))
155 /* --- Set up the alarm, remembering when it's meant to go off --- */
158 if (al && al < LOCK_TIMEOUT)
164 /* --- Set up the return context for the signal handler --- */
167 sigprocmask(SIG_SETMASK, &oss, 0);
173 /* --- Unblock the signal and we're ready --- */
175 if (sigprocmask(SIG_SETMASK, &oss, 0)) {
183 e = fcntl(fd, F_SETLKW, &fk);
185 /* --- Tidy up the mess I left --- */
189 alarm(al - d + left);
191 sigaction(SIGALRM, &osa, 0);
195 /*----- That's all, fokls -------------------------------------------------*/