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From: kvancamp@ARDEC.arpa (Kenneth Van Camp -FSAC-)
Newsgroups: comp.unix.questions
Subject: bg process into fg
Message-ID: <7338@brl-adm.ARPA>
Date: Tue, 12-May-87 14:41:59 EDT
Article-I.D.: brl-adm.7338
Posted: Tue May 12 14:41:59 1987
Date-Received: Fri, 15-May-87 02:23:33 EDT
Sender: news@brl-adm.ARPA
Lines: 68

Is there a way to get a background process into the foreground in System V?
I know about C-shell's 'fg' command, but this won't work because (1) our
Silicon Graphics System V system doesn't support this aspect of the C-shell,
and (2) the process needs to be brought into the foreground after being
created from a different shell (i.e., I need to logout after creating the
background process).
	Here's the problem: I have a C program (and all the source code, so 
I can consider C solutions as well as shell solutions) that does alot of 
number crunching.  Typical runs take several hours, and sometimes as long as 
a day.  Since I can't tie up my terminal during all that time, it naturally 
has to be run in the background.  At this time I may logout.  However, 
during the middle of a long run I would like to log back in and 
interrogate/modify the run.  To do this, I have set up signal interrupts 
(available via the normal Kill command) to alert the program that I wish to 
interrogate the model.  Doing normal printf stuff, I never see the output on 
my terminal because the process is background.  I need a way to bring it 
into the foreground so I can interact with it.  
	Alternatively, I can just write to the tty device directly. I tried
this, and it worked for output but not for input. Here's an example, which
always reports num=0 and does not wait for user response. I'd appreciate
any suggestions.

/* testbg.c: test writing/reading from background process */
#include <stdio.h>
#include <sys/signal.h>

int	useio = 0;
main()
{
	FILE	*filout, *filin, *fopen();
	int	(*s16_svc())();
	int	num;

	signal (SIGUSR1, s16_svc);
	while(1)
		if (useio){
			filout = fopen ("/dev/console", "w");
			filin  = fopen ("/dev/console", "r");
			fprintf (filout,"Enter a number:\n");
			fscanf (filin, &num);
			fprintf (filout,"Read number %d\n", num);
			fclose (filout);
			fclose (filin);
			useio = 0;
		}
}

/* s16_svc: signal 16 service routine. Sets the global useio flag the first
 * five times it is called; the sixth time it stops the program.
 */
int (*s16_svc (sig))()
int sig;
{
	static int count = 0;

	if (++count > 5)
		exit(0);
	/* reset the signal so it works again */
	signal (SIGUSR1, s16_svc);
	/* set the global flag to use the i/o */
	useio = 1;
}

		    --Ken Van Camp <kvancamp@ARDEC.ARPA>
	  Army Armament Research Development & Engineering Center
		        SMCAR-FSA-E  Building 329
			  Dover, NJ  07806-5000
		      (201)724-3334  (AV)880-3334