4.3BSD/usr/contrib/mh/miscellany/less/signal.c

/*
 * Routines dealing with signals.
 *
 * A signal usually merely causes a bit to be set in the "signals" word.
 * At some convenient time, the mainline code checks to see if any
 * signals need processing by calling psignal().
 * An exception is made if we are reading from the keyboard when the
 * signal is received.  Some operating systems will simply call the
 * signal handler and NOT return from the read (with EINTR).
 * To handle this case, we service the interrupt directly from
 * the handler if we are reading from the keyboard.
 */

#include "less.h"
#include <signal.h>
#include <setjmp.h>

/*
 * The type of signal handler functions.
 * Usually int, although it should be void.
 */
typedef	int		HANDLER;

/*
 * "sigs" contains bits indicating signals which need to be processed.
 */
public int sigs;
#define	S_INTERRUPT	01
#ifdef SIGTSTP
#define	S_STOP		02
#endif
#ifdef	NRTC
#define	S_QUIT		04
#endif	NRTC

extern int reading;
extern char *first_cmd;
extern jmp_buf main_loop;

/*
 * Interrupt signal handler.
 */
	static HANDLER
interrupt()
{
	SIGNAL(SIGINT, interrupt);
	sigs |= S_INTERRUPT;
	if (reading)
		psignals();
}

#ifdef	NRTC
/*
 * Interrupt signal handler.
 */
	static HANDLER
quitnow ()
{
	SIGNAL(SIGQUIT, quitnow);
	sigs |= S_QUIT;
	if (reading)
		psignals();
}
#endif	NRTC

#ifdef SIGTSTP
/*
 * "Stop" (^Z) signal handler.
 */
	static HANDLER
stop()
{
	SIGNAL(SIGTSTP, stop);
	sigs |= S_STOP;
	if (reading)
		psignals();
}
#endif

/*
 * Set up the signal handlers.
 */
	public void
init_signals()
{
	(void) SIGNAL(SIGINT, interrupt);
#ifdef	NRTC
	(void) SIGNAL (SIGQUIT, quitnow);
#endif	NRTC
#ifdef SIGTSTP
	(void) SIGNAL(SIGTSTP, stop);
#endif
}

/*
 * Process any signals we have recieved.
 * A received signal cause a bit to be set in "sigs".
 */
	public void 
psignals()
{
	register int tsignals;

	tsignals = sigs;
	sigs = 0;
	if (tsignals == 0)
		return;

	dropout();		/* Discard any buffered output */

#ifdef SIGTSTP
	if (tsignals & S_STOP)
	{
		/*
		 * Clean up the terminal.
		 */
#ifdef SIGTTOU
		SIGNAL(SIGTTOU, SIG_IGN);
#endif
		lower_left();
		clear_eol();
		flush();
		raw_mode(0);
#ifdef SIGTTOU
		SIGNAL(SIGTTOU, SIG_DFL);
#endif
		SIGNAL(SIGTSTP, SIG_DFL);
#if SIGSETMASK
		/*
		 * This system will not allow us to send a 
		 * stop signal (SIGTSTP) to ourself
		 * while we are in the signal handler, like maybe now.
		 * (This can be the case if we are reading; see comment above.)
		 * So we ask the silly system for permission to do so.
		 */
		sigsetmask(0);
#endif
		kill(getpid(), SIGTSTP);
		/*
		 * ... Bye bye. ...
		 * Hopefully we'll be back later and resume here...
		 * Reset the terminal and arrange to repaint the
		 * screen when we get back to the main command loop.
		 */
		SIGNAL(SIGTSTP, stop);
		raw_mode(1);
		first_cmd = "r";
		longjmp(main_loop, 1);
	}
#endif
#ifdef	NRTC
	if (tsignals & S_QUIT)
		quit ();
#endif	NRTC
	if (tsignals & S_INTERRUPT)
	{
		bell();
		/*
		 * {{ You may wish to replace the bell() with 
		 *    error("Interrupt"); }}
		 */
	}

	longjmp(main_loop, 1);
}

/*
 * Pass the specified command to a shell to be executed.
 * Like plain "system()", but handles resetting terminal modes, etc.
 */
	public void
lsystem(cmd)
	char *cmd;
{
	int inp;

	/*
	 * Print the command which is to be executed.
	 */
	lower_left();
	clear_eol();
	puts("!");
	puts(cmd);
	puts("\n");

	/*
	 * De-initialize the terminal and take out of raw mode.
	 */
	deinit();
	flush();
	raw_mode(0);

	/*
	 * Restore signals to their defaults.
	 */
	SIGNAL(SIGINT, SIG_DFL);
#ifdef SIGTSTP
	SIGNAL(SIGTSTP, SIG_DFL);
#endif
	/*
	 * Pass the command to the system to be executed.
	 */
	inp = dup(0);
	close(0);
	open("/dev/tty", 0);

	system(cmd);

	close(0);
	dup(inp);
	close(inp);

	/*
	 * Reset signals, raw mode, etc.
	 */
	init_signals();
	raw_mode(1);
	init();
}