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/***************************************************************************
* COPYRIGHT NOTICE *
****************************************************************************
* ncurses is copyright (C) 1992-1995 *
* Zeyd M. Ben-Halim *
* zmbenhal@netcom.com *
* Eric S. Raymond *
* esr@snark.thyrsus.com *
* *
* Permission is hereby granted to reproduce and distribute ncurses *
* by any means and for any fee, whether alone or as part of a *
* larger distribution, in source or in binary form, PROVIDED *
* this notice is included with any such distribution, and is not *
* removed from any of its header files. Mention of ncurses in any *
* applications linked with it is highly appreciated. *
* *
* ncurses comes AS IS with no warranty, implied or expressed. *
* *
***************************************************************************/
/*
** lib_tstp.c
**
** The routine _nc_signal_handler().
**
*/
#include "curses.priv.h"
#include <signal.h>
#include <stdlib.h>
#if HAVE_SIGACTION
#if !HAVE_TYPE_SIGACTION
typedef struct sigaction sigaction_t;
#endif
#else
#include "SigAction.h"
#endif
#ifdef SVR4_ACTION
#define _POSIX_SOURCE
#endif
/*
* Note: This code is fragile! Its problem is that different OSs
* handle restart of system calls interrupted by signals differently.
* The ncurses code needs signal-call restart to happen -- otherwise,
* interrupted wgetch() calls will return FAIL, probably making the
* application think the input stream has ended and it should
* terminate. In particular, you know you have this problem if, when
* you suspend an ncurses-using lynx with ^Z and resume, it dies
* immediately.
*
* Default behavior of POSIX sigaction(2) is not to restart
* interrupted system calls, but Linux's sigaction does it anyway (at
* least, on and after the 1.1.47 I (esr) use). Thus this code works
* OK under Linux. The 4.4BSD sigaction(2) supports a (non-portable)
* SA_RESTART flag that forces the right behavior. Thus, this code
* should work OK under BSD/OS, NetBSD, and FreeBSD (let us know if it
* does not).
*
* Stock System Vs (and anything else using a strict-POSIX
* sigaction(2) without SA_RESTART) may have a problem. Possible
* solutions:
*
* sigvec restarts by default (SV_INTERRUPT flag to not restart)
* signal restarts by default in SVr4 (assuming you link with -lucb)
* and BSD, but not SVr3.
* sigset restarts, but is only available under SVr4/Solaris.
*
* The signal(3) call is mandated by the ANSI standard, and its
* interaction with sigaction(2) is described in the POSIX standard
* (3.3.4.2, page 72,line 934). According to section 8.1, page 191,
* however, signal(3) itself is not required by POSIX.1. And POSIX is
* silent on whether it is required to restart signals.
*
* So. The present situation is, we use sigaction(2) with no
* guarantee of restart anywhere but on Linux and BSD. We could
* switch to signal(3) and collar Linux, BSD, and SVr4. Any way
* we slice it, System V UNIXes older than SVr4 will probably lose
* (this may include XENIX).
*
* This implementation will probably be changed to use signal(3) in
* the future. If nothing else, it's simpler...
*/
#ifdef SIGTSTP
static void tstp(int dummy)
{
sigset_t mask, omask;
sigaction_t act, oact;
T(("tstp() called"));
/*
* The user may have changed the prog_mode tty bits, so save them.
*/
def_prog_mode();
/*
* Block window change and timer signals. The latter
* is because applications use timers to decide when
* to repaint the screen.
*/
(void)sigemptyset(&mask);
(void)sigaddset(&mask, SIGALRM);
#ifdef SIGWINCH
(void)sigaddset(&mask, SIGWINCH);
#endif
(void)sigprocmask(SIG_BLOCK, &mask, &omask);
/*
* End window mode, which also resets the terminal state to the
* original (pre-curses) modes.
*/
endwin();
/* Unblock SIGTSTP. */
(void)sigemptyset(&mask);
(void)sigaddset(&mask, SIGTSTP);
(void)sigprocmask(SIG_UNBLOCK, &mask, NULL);
/* Now we want to resend SIGSTP to this process and suspend it */
act.sa_handler = SIG_DFL;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
#ifdef SA_RESTART
act.sa_flags |= SA_RESTART;
#endif /* SA_RESTART */
sigaction(SIGTSTP, &act, &oact);
kill(getpid(), SIGTSTP);
/* Process gets suspended...time passes...process resumes */
T(("SIGCONT received"));
sigaction(SIGTSTP, &oact, NULL);
flushinp();
/*
* If the user modified the tty state while suspended, he wants
* those changes to stick. So save the new "default" terminal state.
*/
def_shell_mode();
/*
* This relies on the fact that doupdate() will restore the
* program-mode tty state, and issue enter_ca_mode if need be.
*/
doupdate();
/* Reset the signals. */
(void)sigprocmask(SIG_SETMASK, &omask, NULL);
}
#endif /* defined(SIGTSTP) */
static void cleanup(int sig)
{
/*
* Actually, doing any sort of I/O from within an signal handler is
* "unsafe". But we'll _try_ to clean up the screen and terminal
* settings on the way out.
*/
if (sig == SIGINT
|| sig == SIGQUIT) {
sigaction_t act;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
act.sa_handler = SIG_IGN;
if (sigaction(sig, &act, (sigaction_t *)0) == 0) {
endwin();
}
}
exit(1);
}
/*
* If the given signal is still in its default state, set it to the given
* handler.
*/
static int CatchIfDefault(int sig, sigaction_t *act)
{
sigaction_t old_act;
#ifdef SA_RESTART
act->sa_flags |= SA_RESTART;
#endif /* SA_RESTART */
if (sigaction(sig, (sigaction_t *)0, &old_act) == 0
&& old_act.sa_handler == SIG_DFL) {
(void)sigaction(sig, act, (sigaction_t *)0);
return TRUE;
}
return FALSE;
}
/*
* This is invoked once at the beginning (e.g., from 'initscr()'), to
* initialize the signal catchers, and thereafter when spawning a shell (and
* returning) to disable/enable the SIGTSTP (i.e., ^Z) catcher.
*
* If the application has already set one of the signals, we'll not modify it
* (during initialization).
*
* The XSI document implies that we shouldn't keep the SIGTSTP handler if
* the caller later changes its mind, but that doesn't seem correct.
*/
void _nc_signal_handler(bool enable)
{
#ifdef SIGTSTP /* Xenix 2.x doesn't have this */
static sigaction_t act, oact;
static int ignore;
if (!ignore)
{
if (!enable)
{
act.sa_handler = SIG_IGN;
sigaction(SIGTSTP, &act, &oact);
}
else if (act.sa_handler)
{
sigaction(SIGTSTP, &oact, NULL);
}
else /*initialize */
{
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
#ifdef SA_RESTART
act.sa_flags |= SA_RESTART;
#endif /* SA_RESTART */
act.sa_handler = cleanup;
CatchIfDefault(SIGINT, &act);
CatchIfDefault(SIGTERM, &act);
act.sa_handler = tstp;
if (!CatchIfDefault(SIGTSTP, &act))
ignore = TRUE;
}
}
#else
if (enable)
{
static sigaction_t act;
act.sa_handler = cleanup;
CatchIfDefault(SIGINT, &act);
CatchIfDefault(SIGTERM, &act);
}
#endif
}
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