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 }