myspin1.c

/* 
 * myspin1 - Shell lab test program. 
 *
 * When called by the shell driver, it synchronizes using a two-way
 * handshake. This allows the driver to know that the job is available
 * to receive signals. If it doesn't hear from the driver after some
 * period of time, then it times out and terminates.
 * 
 * When called standalone, it sleeps for [secs] seconds and then 
 * exits. If no argument is given, it sleeps for a default number
 * of seconds. 
 * 
 * Usage: ./myspin1 [secs]
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <string.h>

#include "config.h"

char buf[MAXBUF];
int syncfd;

void sigalrm_handler(int signum) 
{
	exit(0);
}

void sigterm_handler(int signum)
{
	int rc;
	char *cmdp;

	printf("Took SIGTERM!\n");
	fflush(stdout);
	cmdp = "";
	if ((rc = recv(syncfd, buf, MAXBUF, 0)) < 0) {
		perror("recv");
		exit(1);
	}
	if ((rc = send(syncfd, cmdp, strlen(cmdp), 0)) < 0) {
		perror("send");
		exit(1);
	}
	exit(0);
}



int main(int argc, char **argv) 
{
	int rc;
	int standalone;
	char *str;
	char *cmdp;
	struct stat stat;

	signal(SIGALRM, sigalrm_handler);
	signal(SIGTERM, sigterm_handler);

	/* 
	 * Determine if the shell is running standalone or under the
	 * control of the driver program. If running under the driver, get
	 * the number of the driver's synchronizing domain socket
	 * descriptor.  
	 */
	standalone = 1;
	if ((str = getenv("SYNCFD")) != NULL) {
		syncfd = atoi(str);              /* Get descriptor number */
		if (fstat(syncfd, &stat) != -1)  /* Is is open? */
			standalone = 0;
	}

	/* 
	 * If the job is being run by the driver, then synchronize with
	 * the driver over its synchronizing domain socket.  Ignore any
	 * command line argument.  
	 */

	if (!standalone) {
		alarm(JOB_TIMEOUT);
		cmdp = "";
		if ((rc = send(syncfd, cmdp, strlen(cmdp), 0)) < 0) {
			perror("send");
			exit(1);
		}
		if ((rc = recv(syncfd, buf, MAXBUF, 0)) < 0) {
			perror("recv");
			exit(1);
		}
		exit(0);
	}
	/*
	 * Otherwise spin until timing out 
	 */
	else {
		if (argc > 1)
			alarm(atoi(argv[1]));
		else
			alarm(JOB_TIMEOUT);

		while(1);
	}

	/* Control should never reach here */
	exit(1);
}