5d6e6e45dcd8e728c1bfcc6e08899bf08d4fc512
[paraslash.git] / signal.c
1 /*
2 * Copyright (C) 2004 Andre Noll <maan@tuebingen.mpg.de>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6 /** \file signal.c Signal handling functions. */
7
8 #include <signal.h>
9 #include <sys/types.h>
10 #include <regex.h>
11
12 #include "para.h"
13 #include "error.h"
14 #include "fd.h"
15 #include "list.h"
16 #include "string.h"
17 #include "sched.h"
18 #include "signal.h"
19
20 static int signal_pipe[2];
21
22 /**
23 * Initialize the paraslash signal subsystem.
24 *
25 * This function creates a pipe, the signal pipe, to deliver pending
26 * signals to the application (Bernstein's trick). It should be called
27 * during the application's startup part, followed by subsequent calls
28 * to para_install_sighandler() for each signal that should be caught.
29 *
30 * A generic signal handler is used for all signals simultaneously. When a
31 * signal arrives, the signal handler writes the number of the signal received
32 * to one end of the signal pipe. The application can test for pending signals
33 * by checking if the file descriptor of the other end of the signal pipe is
34 * ready for reading, see select(2).
35 *
36 * \return This function either succeeds or calls exit(2) to terminate the
37 * current process. On success, a signal task structure is returned.
38 */
39 struct signal_task *signal_init_or_die(void)
40 {
41 struct signal_task *st;
42 int ret;
43
44 PARA_NOTICE_LOG("setting up signal handling\n");
45 if (pipe(signal_pipe) < 0) {
46 ret = -ERRNO_TO_PARA_ERROR(errno);
47 goto err_out;
48 }
49 ret = mark_fd_nonblocking(signal_pipe[0]);
50 if (ret < 0)
51 goto err_out;
52 ret = mark_fd_nonblocking(signal_pipe[1]);
53 if (ret < 0)
54 goto err_out;
55 st = para_calloc(sizeof(*st));
56 st->fd = signal_pipe[0];
57 return st;
58 err_out:
59 PARA_EMERG_LOG("%s\n", para_strerror(-ret));
60 exit(EXIT_FAILURE);
61 }
62
63 /* Write the signal number to signal pipe. */
64 static void generic_signal_handler(int s)
65 {
66 /*
67 * Signal handlers that make system calls must save a copy of errno on
68 * entry to the handler and restore it on exit, to prevent the
69 * possibility of overwriting a errno value that had previously been
70 * set in the main program.
71 */
72 int save_errno = errno;
73 ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
74
75 if (ret == sizeof(int)) {
76 errno = save_errno;
77 return;
78 }
79 if (ret < 0)
80 PARA_EMERG_LOG("%s\n", strerror(errno));
81 else
82 PARA_EMERG_LOG("short write to signal pipe\n");
83 exit(EXIT_FAILURE);
84 }
85
86 /**
87 * Reap one child.
88 *
89 * \param pid In case a child died, its pid is returned here.
90 *
91 * Call waitpid() and print a log message containing the pid and the cause of
92 * the child's death.
93 *
94 * \return A (negative) paraslash error code on errors, zero, if no child died,
95 * one otherwise. If and only if the function returns one, the content of \a
96 * pid is meaningful.
97 *
98 * \sa waitpid(2).
99 */
100 int para_reap_child(pid_t *pid)
101 {
102 int status;
103 *pid = waitpid(-1, &status, WNOHANG);
104
105 if (!*pid)
106 return 0;
107 if (*pid < 0)
108 return -ERRNO_TO_PARA_ERROR(errno);
109 if (WIFEXITED(status))
110 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
111 WEXITSTATUS(status));
112 else if (WIFSIGNALED(status))
113 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
114 WTERMSIG(status));
115 else
116 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
117 return 1;
118 }
119
120 /**
121 * Install the given handler for the given signal.
122 *
123 * \param sig The number of the signal to catch.
124 * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
125 *
126 * This either succeeds or calls exit(EXIT_FAILURE).
127 *
128 * \sa sigaction(2).
129 */
130 void para_sigaction(int sig, void (*handler)(int))
131 {
132 struct sigaction act;
133
134 PARA_DEBUG_LOG("catching signal %d\n", sig);
135 act.sa_handler = handler;
136 sigemptyset(&act.sa_mask);
137 act.sa_flags = 0;
138 if (sig == SIGALRM) {
139 #ifdef SA_INTERRUPT /* SunOS */
140 act.sa_flags |= SA_INTERRUPT;
141 #endif
142 } else {
143 #ifdef SA_RESTART /* BSD */
144 act.sa_flags |= SA_RESTART;
145 #endif
146 }
147 if (sigaction(sig, &act, NULL) >= 0)
148 return;
149 PARA_EMERG_LOG("failed to install signal handler for signal %d\n",
150 sig);
151 exit(EXIT_FAILURE);
152 }
153
154 /**
155 * Install the generic signal handler for the given signal number.
156 *
157 * \param sig The number of the signal to catch.
158 *
159 * \sa signal(2), sigaction(2).
160 */
161 void para_install_sighandler(int sig)
162 {
163 para_sigaction(sig, &generic_signal_handler);
164 }
165
166 /**
167 * Block a signal for the caller.
168 *
169 * \param sig The signal to block.
170 *
171 * This sets the given signal in the current signal mask of the calling process
172 * to prevent this signal from delivery.
173 *
174 * \sa \ref para_unblock_signal(), sigprocmask(2), sigaddset(3).
175 */
176 void para_block_signal(int sig)
177 {
178 sigset_t set;
179
180 PARA_DEBUG_LOG("blocking signal %d\n", sig);
181 sigemptyset(&set);
182 sigaddset(&set, sig);
183 sigprocmask(SIG_BLOCK, &set, NULL);
184 }
185
186 /**
187 * Unblock a signal.
188 *
189 * \param sig The signal to unblock.
190 *
191 * This function removes the given signal from the current set of blocked
192 * signals.
193 *
194 * \sa \ref para_block_signal(), sigprocmask(2), sigaddset(3).
195 */
196 void para_unblock_signal(int sig)
197 {
198 sigset_t set;
199
200 PARA_DEBUG_LOG("unblocking signal %d\n", sig);
201 sigemptyset(&set);
202 sigaddset(&set, sig);
203 sigprocmask(SIG_UNBLOCK, &set, NULL);
204 }
205
206 /**
207 * Return the number of the next pending signal.
208 *
209 * \param rfds The fd_set containing the signal pipe.
210 *
211 * \return On success, the number of the received signal is returned. If there
212 * is no signal currently pending, the function returns zero. On read errors
213 * from the signal pipe, the process is terminated.
214 */
215 int para_next_signal(fd_set *rfds)
216 {
217 size_t n;
218 int s, ret = read_nonblock(signal_pipe[0], &s, sizeof(s), rfds, &n);
219
220 if (ret < 0) {
221 PARA_EMERG_LOG("%s\n", para_strerror(-ret));
222 exit(EXIT_FAILURE);
223 }
224 if (n == 0)
225 return 0;
226 assert(n == sizeof(s));
227 PARA_DEBUG_LOG("next signal: %d\n", s);
228 return s;
229 }
230
231 /**
232 * Close the write end of the signal pipe, deallocate resources.
233 *
234 * \param st The pointer obtained earlier from signal_init_or_die().
235 */
236 void signal_shutdown(struct signal_task *st)
237 {
238 close(signal_pipe[1]);
239 free(st);
240 }