lockit.c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· C语言 代码 · 共 180 行

#ifndef lint
static	char	*sccsid = "@(#)lockit.c	4.1	(ULTRIX)	7/17/90";
#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.	*
 *									*
 ************************************************************************/
/*
 * Modification history
 *
 * 29 Jun 88 -- D. Long
 *	Modified to detect failure on write to lock file. Uses xwrite.
 */

/*
	Process semaphore.
	Try repeatedly (`count' times) to create `lockfile' mode 444.
	Sleep 10 seconds between tries.
	If `tempfile' is successfully created, write the process ID
	`pid' in `tempfile' (in binary), link `tempfile' to `lockfile',
	and return 0.
	If `lockfile' exists and it hasn't been modified within the last
	minute, and either the file is empty or the process ID contained
	in the file is not the process ID of any existing process,
	`lockfile' is removed and it tries again to make `lockfile'.
	After `count' tries, or if the reason for the create failing
	is something other than EACCES, return xmsg().
 
	Unlockit will return 0 if the named lock exists, contains
	the given pid, and is successfully removed; -1 otherwise.
*/

# include	"sys/types.h"
# include	"macros.h"
# include	"errno.h"

lockit(lockfile,count,pid)
register char *lockfile;
register unsigned count;
unsigned pid;
{
	register int fd;
	int ret;
	unsigned opid;
	long ltime;
	long omtime;
	extern int errno;
	static char tempfile[512];
	char	dir_name[512];

	copy(lockfile,dir_name);
	sprintf(tempfile,"%s/%u.%ld",dname(dir_name),pid,time((long *)0));

	for (++count; --count; sleep(10)) {
		if (onelock(pid,tempfile,lockfile) == 0)
			return(0);
		if (!exists(lockfile))
			continue;
		omtime = Statbuf.st_mtime;
		if ((fd = open(lockfile,0)) < 0)
			continue;
		ret = read(fd,&opid,sizeof(opid));
		close(fd);
		if (ret != sizeof(pid) || ret != Statbuf.st_size) {
			unlink(lockfile);
			continue;
		}
		/* check for pid */
		if (kill(opid,0) == -1 && errno == ESRCH) {
			if (exists(lockfile) &&
				omtime == Statbuf.st_mtime) {
					unlink(lockfile);
					continue;
			}
		}
		if ((ltime = time((long *)0) - Statbuf.st_mtime) < 60L) {
			if (ltime >= 0 && ltime < 60)
				sleep(60 - ltime);
			else
				sleep(60);
		}
		continue;
	}
	return(-1);
}


unlockit(lockfile,pid)
register char *lockfile;
unsigned pid;
{
	register int fd, n;
	unsigned opid;

	if ((fd = open(lockfile,0)) < 0)
		return(-1);
	n = read(fd,&opid,sizeof(opid));
	close(fd);
	if (n == sizeof(opid) && opid == pid)
		return(unlink(lockfile));
	else
		return(-1);
}


onelock(pid,tempfile,lockfile)
unsigned pid;
char *tempfile;
char *lockfile;
{
	int fd, n;
	extern int errno;

	if ((fd = creat(tempfile,0444)) >= 0) {
		n = write(fd,&pid,sizeof(pid));
		close(fd);
		if(n != sizeof pid) {
			unlink(tempfile);
			xmsg(tempfile, "lockit");
		}
		if (link(tempfile,lockfile) < 0) {
			unlink(tempfile);
			return(-1);
		}
		unlink(tempfile);
		return(0);
	}
	if (errno == ENFILE) {
		unlink(tempfile);
		return(-1);
	}
	if (errno != EACCES)
		return(xmsg(tempfile,"lockit"));
	return(-1);
}


mylock(lockfile,pid)
register char *lockfile;
unsigned pid;
{
	register int fd, n;
	unsigned opid;

	if ((fd = open(lockfile,0)) < 0)
		return(0);
	n = read(fd,&opid,sizeof(opid));
	close(fd);
	if (n == sizeof(opid) && opid == pid)
		return(1);
	else
		return(0);
}