Merge branch 'refs/heads/t/ff'
[paraslash.git] / signal.c
1 /* Copyright (C) 2004 Andre Noll <maan@tuebingen.mpg.de>, see file COPYING. */
2 /** \file signal.c Signal handling functions. */
3
4 #include <signal.h>
5 #include <sys/types.h>
6 #include <regex.h>
7
8 #include "para.h"
9 #include "error.h"
10 #include "fd.h"
11 #include "list.h"
12 #include "string.h"
13 #include "sched.h"
14 #include "signal.h"
15
16 static int signal_pipe[2];
17
18 /**
19 * Initialize the paraslash signal subsystem.
20 *
21 * This function creates a pipe, the signal pipe, to deliver pending
22 * signals to the application (Bernstein's trick). It should be called
23 * during the application's startup part, followed by subsequent calls
24 * to \ref para_install_sighandler() for each signal that should be caught.
25 *
26 * A generic signal handler is used for all signals simultaneously. When a
27 * signal arrives, the signal handler writes the number of the signal received
28 * to one end of the signal pipe. The application can test for pending signals
29 * by checking if the file descriptor of the other end of the signal pipe is
30 * ready for reading, see select(2).
31 *
32 * \return This function either succeeds or calls exit(3) to terminate the
33 * current process. On success, a signal task structure is returned.
34 */
35 struct signal_task *signal_init_or_die(void)
36 {
37 struct signal_task *st;
38 int ret;
39
40 PARA_NOTICE_LOG("setting up signal handling\n");
41 if (pipe(signal_pipe) < 0) {
42 ret = -ERRNO_TO_PARA_ERROR(errno);
43 goto err_out;
44 }
45 ret = mark_fd_nonblocking(signal_pipe[0]);
46 if (ret < 0)
47 goto err_out;
48 ret = mark_fd_nonblocking(signal_pipe[1]);
49 if (ret < 0)
50 goto err_out;
51 st = para_calloc(sizeof(*st));
52 st->fd = signal_pipe[0];
53 return st;
54 err_out:
55 PARA_EMERG_LOG("%s\n", para_strerror(-ret));
56 exit(EXIT_FAILURE);
57 }
58
59 /* Write the signal number to signal pipe. */
60 static void generic_signal_handler(int s)
61 {
62 /*
63 * Signal handlers that make system calls must save a copy of errno on
64 * entry to the handler and restore it on exit, to prevent the
65 * possibility of overwriting a errno value that had previously been
66 * set in the main program.
67 */
68 int save_errno = errno;
69 ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
70
71 if (ret == sizeof(int)) {
72 errno = save_errno;
73 return;
74 }
75 if (ret < 0)
76 PARA_EMERG_LOG("%s\n", strerror(errno));
77 else
78 PARA_EMERG_LOG("short write to signal pipe\n");
79 exit(EXIT_FAILURE);
80 }
81
82 /**
83 * Reap one child.
84 *
85 * \param pid In case a child died, its pid is returned here.
86 *
87 * Call waitpid() and print a log message containing the pid and the cause of
88 * the child's death.
89 *
90 * \return A (negative) paraslash error code on errors, zero, if no child died,
91 * one otherwise. If and only if the function returns one, the content of \a
92 * pid is meaningful.
93 *
94 * \sa waitpid(2).
95 */
96 int para_reap_child(pid_t *pid)
97 {
98 int status;
99 *pid = waitpid(-1, &status, WNOHANG);
100
101 if (!*pid)
102 return 0;
103 if (*pid < 0)
104 return -ERRNO_TO_PARA_ERROR(errno);
105 if (WIFEXITED(status))
106 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
107 WEXITSTATUS(status));
108 else if (WIFSIGNALED(status))
109 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
110 WTERMSIG(status));
111 else
112 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
113 return 1;
114 }
115
116 /**
117 * Install the given handler for the given signal.
118 *
119 * \param sig The number of the signal to catch.
120 * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
121 *
122 * This either succeeds or calls exit(EXIT_FAILURE).
123 *
124 * \sa sigaction(2).
125 */
126 void para_sigaction(int sig, void (*handler)(int))
127 {
128 struct sigaction act;
129
130 PARA_DEBUG_LOG("catching signal %d\n", sig);
131 act.sa_handler = handler;
132 sigemptyset(&act.sa_mask);
133 act.sa_flags = 0;
134 if (sig == SIGALRM) {
135 #ifdef SA_INTERRUPT /* SunOS */
136 act.sa_flags |= SA_INTERRUPT;
137 #endif
138 } else {
139 #ifdef SA_RESTART /* BSD */
140 act.sa_flags |= SA_RESTART;
141 #endif
142 }
143 if (sigaction(sig, &act, NULL) >= 0)
144 return;
145 PARA_EMERG_LOG("failed to install signal handler for signal %d\n",
146 sig);
147 exit(EXIT_FAILURE);
148 }
149
150 /**
151 * Install the generic signal handler for the given signal number.
152 *
153 * \param sig The number of the signal to catch.
154 *
155 * \sa signal(2), sigaction(2).
156 */
157 void para_install_sighandler(int sig)
158 {
159 para_sigaction(sig, &generic_signal_handler);
160 }
161
162 /**
163 * Block a signal for the caller.
164 *
165 * \param sig The signal to block.
166 *
167 * This sets the given signal in the current signal mask of the calling process
168 * to prevent this signal from delivery.
169 *
170 * \sa \ref para_unblock_signal(), sigprocmask(2), sigaddset(3).
171 */
172 void para_block_signal(int sig)
173 {
174 sigset_t set;
175
176 PARA_DEBUG_LOG("blocking signal %d\n", sig);
177 sigemptyset(&set);
178 sigaddset(&set, sig);
179 sigprocmask(SIG_BLOCK, &set, NULL);
180 }
181
182 /**
183 * Unblock a signal.
184 *
185 * \param sig The signal to unblock.
186 *
187 * This function removes the given signal from the current set of blocked
188 * signals.
189 *
190 * \sa \ref para_block_signal(), sigprocmask(2), sigaddset(3).
191 */
192 void para_unblock_signal(int sig)
193 {
194 sigset_t set;
195
196 PARA_DEBUG_LOG("unblocking signal %d\n", sig);
197 sigemptyset(&set);
198 sigaddset(&set, sig);
199 sigprocmask(SIG_UNBLOCK, &set, NULL);
200 }
201
202 /**
203 * Return the number of the next pending signal.
204 *
205 * \param rfds The fd_set containing the signal pipe.
206 *
207 * \return On success, the number of the received signal is returned. If there
208 * is no signal currently pending, the function returns zero. On read errors
209 * from the signal pipe, the process is terminated.
210 */
211 int para_next_signal(fd_set *rfds)
212 {
213 size_t n;
214 int s, ret = read_nonblock(signal_pipe[0], &s, sizeof(s), rfds, &n);
215
216 if (ret < 0) {
217 PARA_EMERG_LOG("%s\n", para_strerror(-ret));
218 exit(EXIT_FAILURE);
219 }
220 if (n == 0)
221 return 0;
222 assert(n == sizeof(s));
223 PARA_DEBUG_LOG("next signal: %d\n", s);
224 return s;
225 }
226
227 /**
228 * Close the write end of the signal pipe, deallocate resources.
229 *
230 * \param st The pointer obtained earlier from signal_init_or_die().
231 */
232 void signal_shutdown(struct signal_task *st)
233 {
234 close(signal_pipe[1]);
235 free(st);
236 }