1 /****************************************************************************
2 * Copyright 2020 Thomas E. Dickey *
3 * Copyright 1998-2014,2017 Free Software Foundation, Inc. *
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28 ****************************************************************************/
30 /****************************************************************************
31 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
32 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
33 * and: Thomas E. Dickey 1995-on *
34 ****************************************************************************/
39 ** The routine _nc_signal_handler().
42 #include <curses.priv.h>
44 #include <SigAction.h>
46 MODULE_ID("$Id: lib_tstp.c,v 1.50 2020/02/02 23:34:34 tom Exp $")
48 #if defined(SIGTSTP) && (HAVE_SIGACTION || HAVE_SIGVEC)
88 return "unknown signal";
94 * Note: This code is fragile! Its problem is that different OSs
95 * handle restart of system calls interrupted by signals differently.
96 * The ncurses code needs signal-call restart to happen -- otherwise,
97 * interrupted wgetch() calls will return FAIL, probably making the
98 * application think the input stream has ended and it should
99 * terminate. In particular, you know you have this problem if, when
100 * you suspend an ncurses-using lynx with ^Z and resume, it dies
103 * Default behavior of POSIX sigaction(2) is not to restart
104 * interrupted system calls, but Linux's sigaction does it anyway (at
105 * least, on and after the 1.1.47 I (esr) use). Thus this code works
106 * OK under Linux. The 4.4BSD sigaction(2) supports a (non-portable)
107 * SA_RESTART flag that forces the right behavior. Thus, this code
108 * should work OK under BSD/OS, NetBSD, and FreeBSD (let us know if it
111 * Stock System Vs (and anything else using a strict-POSIX
112 * sigaction(2) without SA_RESTART) may have a problem. Possible
115 * sigvec restarts by default (SV_INTERRUPT flag to not restart)
116 * signal restarts by default in SVr4 (assuming you link with -lucb)
117 * and BSD, but not SVr3.
118 * sigset restarts, but is only available under SVr4/Solaris.
120 * The signal(3) call is mandated by the ANSI standard, and its
121 * interaction with sigaction(2) is described in the POSIX standard
122 * (3.3.4.2, page 72,line 934). According to section 8.1, page 191,
123 * however, signal(3) itself is not required by POSIX.1. And POSIX is
124 * silent on whether it is required to restart signals.
126 * So. The present situation is, we use sigaction(2) with no
127 * guarantee of restart anywhere but on Linux and BSD. We could
128 * switch to signal(3) and collar Linux, BSD, and SVr4. Any way
129 * we slice it, System V UNIXes older than SVr4 will probably lose
130 * (this may include XENIX).
132 * This implementation will probably be changed to use signal(3) in
133 * the future. If nothing else, it's simpler...
138 handle_SIGTSTP(int dummy GCC_UNUSED)
140 SCREEN *sp = CURRENT_SCREEN;
141 sigset_t mask, omask;
142 sigaction_t act, oact;
148 _nc_globals.have_sigtstp = 1;
149 T(("handle_SIGTSTP() called"));
152 * The user may have changed the prog_mode tty bits, so save them.
154 * But first try to detect whether we still are in the foreground
155 * process group - if not, an interactive shell may already have
156 * taken ownership of the tty and modified the settings when our
157 * parent was stopped before us, and we would likely pick up the
158 * settings already modified by the shell.
160 * Don't do this if we're not in curses -
162 if (sp != 0 && (sp->_endwin == ewRunning))
164 if (tcgetpgrp(STDIN_FILENO) == getpgrp())
166 NCURSES_SP_NAME(def_prog_mode) (NCURSES_SP_ARG);
169 * Block window change and timer signals. The latter
170 * is because applications use timers to decide when
171 * to repaint the screen.
173 (void) sigemptyset(&mask);
175 (void) sigaddset(&mask, SIGALRM);
178 (void) sigaddset(&mask, SIGWINCH);
180 (void) sigprocmask(SIG_BLOCK, &mask, &omask);
183 sigttou_blocked = sigismember(&omask, SIGTTOU);
184 if (!sigttou_blocked) {
185 (void) sigemptyset(&mask);
186 (void) sigaddset(&mask, SIGTTOU);
187 (void) sigprocmask(SIG_BLOCK, &mask, NULL);
192 * End window mode, which also resets the terminal state to the
193 * original (pre-curses) modes.
195 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
197 /* Unblock SIGTSTP. */
198 (void) sigemptyset(&mask);
199 (void) sigaddset(&mask, SIGTSTP);
201 if (!sigttou_blocked) {
202 /* Unblock this too if it wasn't blocked on entry */
203 (void) sigaddset(&mask, SIGTTOU);
206 (void) sigprocmask(SIG_UNBLOCK, &mask, NULL);
208 /* Now we want to resend SIGSTP to this process and suspend it */
209 act.sa_handler = SIG_DFL;
210 sigemptyset(&act.sa_mask);
213 act.sa_flags |= SA_RESTART;
214 #endif /* SA_RESTART */
215 sigaction(SIGTSTP, &act, &oact);
216 kill(getpid(), SIGTSTP);
218 /* Process gets suspended...time passes...process resumes */
220 T(("SIGCONT received"));
221 sigaction(SIGTSTP, &oact, NULL);
222 NCURSES_SP_NAME(flushinp) (NCURSES_SP_ARG);
225 * If the user modified the tty state while suspended, he wants
226 * those changes to stick. So save the new "default" terminal state.
228 NCURSES_SP_NAME(def_shell_mode) (NCURSES_SP_ARG);
231 * This relies on the fact that doupdate() will restore the
232 * program-mode tty state, and issue enter_ca_mode if need be.
234 NCURSES_SP_NAME(doupdate) (NCURSES_SP_ARG);
236 /* Reset the signals. */
237 (void) sigprocmask(SIG_SETMASK, &omask, NULL);
239 #endif /* USE_SIGTSTP */
242 handle_SIGINT(int sig)
244 SCREEN *sp = CURRENT_SCREEN;
247 * Much of this is unsafe from a signal handler. But we'll _try_ to clean
248 * up the screen and terminal settings on the way out.
250 * There are at least the following problems:
251 * 1) Walking the SCREEN list is unsafe, since all list management
252 * is done without any signal blocking.
253 * 2) On systems which have REENTRANT turned on, set_term() uses
254 * _nc_lock_global() which could deadlock or misbehave in other ways.
255 * 3) endwin() calls all sorts of stuff, many of which use stdio or
256 * other library functions which are clearly unsafe.
258 if (!_nc_globals.cleanup_nested++
259 && (sig == SIGINT || sig == SIGTERM)) {
260 #if HAVE_SIGACTION || HAVE_SIGVEC
262 sigemptyset(&act.sa_mask);
264 act.sa_handler = SIG_IGN;
265 if (sigaction(sig, &act, NULL) == 0)
267 if (signal(sig, SIG_IGN) != SIG_ERR)
271 for (each_screen(scan)) {
273 && NC_ISATTY(fileno(scan->_ofp))) {
274 scan->_outch = NCURSES_SP_NAME(_nc_outch);
277 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
279 sp->_endwin = ewInitial; /* in case of reuse */
288 handle_SIGWINCH(int sig GCC_UNUSED)
290 _nc_globals.have_sigwinch = 1;
291 # if USE_PTHREADS_EINTR
292 if (_nc_globals.read_thread) {
293 if (!pthread_equal(pthread_self(), _nc_globals.read_thread))
294 pthread_kill(_nc_globals.read_thread, SIGWINCH);
295 _nc_globals.read_thread = 0;
299 #endif /* USE_SIGWINCH */
302 * If the given signal is still in its default state, set it to the given
306 CatchIfDefault(int sig, void (*handler) (int))
309 #if HAVE_SIGACTION || HAVE_SIGVEC
313 memset(&new_act, 0, sizeof(new_act));
314 sigemptyset(&new_act.sa_mask);
319 new_act.sa_flags |= SA_RESTART;
320 #endif /* SA_RESTART */
321 new_act.sa_handler = handler;
323 if (sigaction(sig, NULL, &old_act) == 0
324 && (old_act.sa_handler == SIG_DFL
325 || old_act.sa_handler == handler
327 || (sig == SIGWINCH && old_act.sa_handler == SIG_IGN)
330 (void) sigaction(sig, &new_act, NULL);
335 #else /* !HAVE_SIGACTION */
336 void (*ohandler) (int);
338 ohandler = signal(sig, SIG_IGN);
339 if (ohandler == SIG_DFL
340 || ohandler == handler
342 || (sig == SIGWINCH && ohandler == SIG_IGN)
345 signal(sig, handler);
348 signal(sig, ohandler);
352 T(("CatchIfDefault - will %scatch %s",
353 result ? "" : "not ", signal_name(sig)));
358 * This is invoked once at the beginning (e.g., from 'initscr()'), to
359 * initialize the signal catchers, and thereafter when spawning a shell (and
360 * returning) to disable/enable the SIGTSTP (i.e., ^Z) catcher.
362 * If the application has already set one of the signals, we'll not modify it
363 * (during initialization).
365 * The XSI document implies that we shouldn't keep the SIGTSTP handler if
366 * the caller later changes its mind, but that doesn't seem correct.
369 _nc_signal_handler(int enable)
371 T((T_CALLED("_nc_signal_handler(%d)"), enable));
372 #if USE_SIGTSTP /* Xenix 2.x doesn't have SIGTSTP, for example */
374 static bool ignore_tstp = FALSE;
377 static sigaction_t new_sigaction, old_sigaction;
380 new_sigaction.sa_handler = SIG_IGN;
381 sigaction(SIGTSTP, &new_sigaction, &old_sigaction);
382 } else if (new_sigaction.sa_handler != SIG_DFL) {
383 sigaction(SIGTSTP, &old_sigaction, NULL);
384 } else if (sigaction(SIGTSTP, NULL, &old_sigaction) == 0
385 && (old_sigaction.sa_handler == SIG_DFL)) {
386 sigemptyset(&new_sigaction.sa_mask);
388 new_sigaction.sa_flags |= SA_RESTART;
389 #endif /* SA_RESTART */
390 new_sigaction.sa_handler = handle_SIGTSTP;
391 (void) sigaction(SIGTSTP, &new_sigaction, NULL);
397 #endif /* !USE_SIGTSTP */
399 if (!_nc_globals.init_signals) {
401 CatchIfDefault(SIGINT, handle_SIGINT);
402 CatchIfDefault(SIGTERM, handle_SIGINT);
404 CatchIfDefault(SIGWINCH, handle_SIGWINCH);
406 _nc_globals.init_signals = TRUE;