candidate.c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· C语言 代码 · 共 150 行

#ifndef lint
static	char	*sccsid = "@(#)candidate.c	4.1	(ULTRIX)	7/2/90";
#endif lint

/************************************************************************
 *									*
 *			Copyright (c) 1988 by				*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/
/*
 * Copyright (c) 1983 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 *static char sccsid[] = "@(#)candidate.c	2.3 (Berkeley) 4/21/86";
 */


#include "globals.h"
#include <protocols/timed.h>

#define ELECTIONWAIT	3	/* seconds */

/*
 * `election' candidates a host as master: it is called by a slave 
 * which runs with the -M option set when its election timeout expires. 
 * Note the conservative approach: if a new timed comes up, or another
 * candidate sends an election request, the candidature is withdrawn.
 */

election(net)
struct netinfo *net;
{
	int ret;
	struct tsp *resp, msg, *readmsg();
	struct timeval wait;
	struct tsp *answer, *acksend();
	long casual();
	struct sockaddr_in server;

	syslog(LOG_INFO, "THIS MACHINE IS A CANDIDATE");
	if (trace) {
		fprintf(fd, "THIS MACHINE IS A CANDIDATE\n");
	}

	ret = MASTER;
	slvcount = 1;

	msg.tsp_type = TSP_ELECTION;
	msg.tsp_vers = TSPVERSION;
	(void)strcpy(msg.tsp_name, hostname);
	bytenetorder(&msg);
	if (sendto(sock, (char *)&msg, sizeof(struct tsp), 0, &net->dest_addr,
	    sizeof(struct sockaddr_in)) < 0) {
		syslog(LOG_ERR, "sendto: %m");
		exit(1);
	}

	do {
		wait.tv_sec = ELECTIONWAIT;
		wait.tv_usec = 0;
		resp = readmsg(TSP_ANY, (char *)ANYADDR, &wait, net);
		if (resp != NULL) {
			switch (resp->tsp_type) {

			case TSP_ACCEPT:
				(void) addmach(resp->tsp_name, &from);
				break;

			case TSP_MASTERUP:
			case TSP_MASTERREQ:
				/*
				 * If a timedaemon is coming up at the same time,
				 * give up the candidature: it will be the master.
				 */
				ret = SLAVE;
				break;

			case TSP_QUIT:
			case TSP_REFUSE:
				/*
				 * Collision: change value of election timer 
				 * using exponential backoff.
				 * The value of timer will be recomputed (in slave.c)
				 * using the original interval when election will 
				 * be successfully completed.
				 */
				backoff *= 2;
				delay2 = casual((long)MINTOUT, 
							(long)(MAXTOUT * backoff));
				ret = SLAVE;
				break;

			case TSP_ELECTION:
				/* no master for another round */
				msg.tsp_type = TSP_REFUSE;
				(void)strcpy(msg.tsp_name, hostname);
				server = from;
				answer = acksend(&msg, &server, resp->tsp_name,
				    TSP_ACK, (struct netinfo *)NULL);
				if (answer == NULL) {
					syslog(LOG_ERR, "error in election");
				} else {
					(void) addmach(resp->tsp_name, &from);
				}
				break;

			case TSP_SLAVEUP:
				(void) addmach(resp->tsp_name, &from);
				break;

			case TSP_SETDATE:
			case TSP_SETDATEREQ:
				break;

			default:
				if (trace) {
					fprintf(fd, "candidate: ");
					print(resp, &from);
				}
				break;
			}
		} else {
			break;
		}
	} while (ret == MASTER);
	return(ret);
}