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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: lock.c,v 1.5 1999/06/19 20:35:45 mdw Exp $ |
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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 $ |
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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'. |
35 | * |
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36 | * Revision 1.4 1999/06/19 20:33:16 mdw |
37 | * More sophisticated and excessive signal and alarm handling. |
38 | * |
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39 | * Revision 1.3 1999/06/06 01:23:00 mdw |
40 | * Fix signal handling. |
41 | * |
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42 | * Revision 1.2 1999/05/26 20:53:40 mdw |
43 | * Fixes for stupid bugs. |
44 | * |
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45 | * Revision 1.1 1999/05/15 10:33:53 mdw |
46 | * Add simplified locking code. |
47 | * |
48 | */ |
49 | |
50 | /*----- Header files ------------------------------------------------------*/ |
51 | |
52 | #include <errno.h> |
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53 | #include <setjmp.h> |
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54 | #include <signal.h> |
55 | #include <stdio.h> |
56 | #include <stdlib.h> |
57 | #include <string.h> |
58 | #include <time.h> |
59 | |
60 | #include <sys/types.h> |
61 | #include <unistd.h> |
62 | #include <fcntl.h> |
63 | |
64 | #include "lock.h" |
65 | |
66 | /*----- Tunable constants -------------------------------------------------*/ |
67 | |
68 | #define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */ |
69 | |
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70 | /*----- Static variables --------------------------------------------------*/ |
71 | |
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72 | static jmp_buf jmp; /* Jump here to interrup @fcntl@ */ |
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73 | |
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74 | /*----- Main code ---------------------------------------------------------*/ |
75 | |
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76 | /* --- @sigalrm@ --- * |
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77 | * |
78 | * Arguments: @int sig@ = signal number |
79 | * |
80 | * Returns: --- |
81 | * |
82 | * Use: Makes sure that a @SIGALRM@ signal interrupts system calls. |
83 | */ |
84 | |
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85 | static void sigalrm(int sig) { longjmp(jmp, 1); } |
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86 | |
87 | /* --- @lock_file@ --- * |
88 | * |
89 | * Arguments: @int fd@ = file descriptor to lock |
90 | * @unsigned how@ = type of lock required |
91 | * |
92 | * Returns: 0 if OK, -1 if it failed. |
93 | * |
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 |
99 | * error. |
100 | */ |
101 | |
102 | int lock_file(int fd, unsigned how) |
103 | { |
104 | struct flock fk; |
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105 | struct sigaction sa, osa; |
106 | sigset_t ss, oss; |
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107 | int e; |
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108 | int al, d, left; |
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109 | |
110 | /* --- Fill in the easy bits --- */ |
111 | |
112 | fk.l_whence = SEEK_SET; |
113 | fk.l_start = 0; |
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114 | fk.l_len = 0; |
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115 | |
116 | /* --- Unlocking is really easy --- */ |
117 | |
118 | if (how == LOCK_UNLOCK) { |
119 | fk.l_type = F_UNLCK; |
120 | return (fcntl(fd, F_SETLK, &fk)); |
121 | } |
122 | |
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123 | /* --- Decide how to do the locking --- */ |
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124 | |
125 | if (how == LOCK_EXCL) |
126 | fk.l_type = F_WRLCK; |
127 | else if (how == LOCK_NONEXCL) |
128 | fk.l_type = F_RDLCK; |
129 | else { |
130 | errno = EINVAL; |
131 | return (-1); |
132 | } |
133 | |
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134 | /* --- Block @SIGALRM@ for a while --- * |
135 | * |
136 | * I don't want stray alarms going off while I'm busy here. |
137 | */ |
138 | |
139 | sigemptyset(&ss); |
140 | sigaddset(&ss, SIGALRM); |
141 | if (sigprocmask(SIG_BLOCK, &ss, &oss)) |
142 | return (-1); |
143 | |
144 | /* --- Set up the signal handler --- */ |
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145 | |
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146 | sa.sa_handler = sigalrm; |
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147 | sa.sa_flags = 0; |
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148 | #ifdef SA_INTERRUPT |
149 | sa.sa_flags |= SA_INTERRUPT; |
150 | #endif |
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151 | sigemptyset(&sa.sa_mask); |
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152 | if (sigaction(SIGALRM, &sa, &osa)) |
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153 | return (-1); |
154 | |
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155 | /* --- Set up the alarm, remembering when it's meant to go off --- */ |
156 | |
157 | al = alarm(0); |
158 | if (al && al < LOCK_TIMEOUT) |
159 | d = al; |
160 | else |
161 | d = LOCK_TIMEOUT; |
162 | alarm(d); |
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163 | |
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164 | /* --- Set up the return context for the signal handler --- */ |
165 | |
166 | if (setjmp(jmp)) { |
167 | sigprocmask(SIG_SETMASK, &oss, 0); |
168 | errno = EINTR; |
169 | e = -1; |
170 | goto done; |
171 | } |
172 | |
173 | /* --- Unblock the signal and we're ready --- */ |
174 | |
175 | if (sigprocmask(SIG_SETMASK, &oss, 0)) { |
176 | alarm(al); |
177 | e = -1; |
178 | goto done; |
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179 | } |
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180 | |
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181 | /* --- Do it --- */ |
182 | |
183 | e = fcntl(fd, F_SETLKW, &fk); |
184 | |
185 | /* --- Tidy up the mess I left --- */ |
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186 | |
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187 | left = alarm(0); |
188 | if (al) |
189 | alarm(al - d + left); |
190 | done: |
191 | sigaction(SIGALRM, &osa, 0); |
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192 | return (e); |
193 | } |
194 | |
195 | /*----- That's all, fokls -------------------------------------------------*/ |