The source for the original run-with-lockfile.c code have moved, and is
now available from
URL:
https://raw.githubusercontent.com/mysociety/theyworkforyou/master/scripts/run-with-lockfile.c
.
Since I proposed this package, mysociety have moved to a shell script
variant, available from
URL:
https://raw.githubusercontent.com/mysociety/commonlib/master/bin/run-with-lockfile.sh
.
I've asked the lockfile-progs package maintainer in bug #741300 if he
would be willing to include the shell script there instead of creating a
new package for so little code, but have not received any feedback in
URL: http://bugs.debian.org/741300 yet.
The C version look like this:
/*
* run-with-lockfile.c:
* Lock a file and then execute a program.
*
* Copyright (c) 2003 Chris Lightfoot. All rights reserved.
* Email: ch...@ex-parrot.com; WWW: http://www.ex-parrot.com/~chris/
*
* Chris has kindly licensed this under the GPL.
*
*/
static const char rcsid[] = $Id: run-with-lockfile.c,v 1.1 2006-04-27 14:20:20
twfy-live Exp $;
#include sys/types.h
#include errno.h
#include fcntl.h
#include stdio.h
#include stdlib.h
#include string.h
#include unistd.h
#include sys/stat.h
void usage(FILE *fp) {
fprintf(fp,
run-with-lockfile [-n] FILE COMMAND\n
\n
Open (perhaps create) and fcntl-lock FILE, then run COMMAND. If option -n\n
is given, fail immediately if the lock is held by another process;\n
otherwise, wait for the lock. When COMMAND is run, the variable LOCKFILE\n
will be set to FILE in its environment. COMMAND is run by passing it to\n
/bin/sh with the -c parameter.\n
\n
Exit value is that returned from COMMAND; or, if -n is given and the lock\n
could not be obtained, 100; or, if another error occurs, 101.\n
\n
Copyright (c) 2003-4 Chris Lightfoot, Mythic Beasts Ltd.\n
%s\n,
rcsid
);
}
int main(int argc, char *argv[]) {
char *file, *command, *envvar;
int wait = 1, n;
int fd;
struct stat st;
struct flock fl;
if (argv[1] (0 == strcmp(argv[1], -h) || 0 == strcmp(argv[1],
--help))) {
usage(stdout);
return 0;
}
if (argc == 4) {
if (strcmp(argv[1], -n) != 0) {
fprintf(stderr, run-with-lockfile: `%s' is not a valid option\n,
argv[1]);
usage(stderr);
return 101;
} else {
wait = 0;
--argc;
++argv;
}
}
if (argc != 3) {
fprintf(stderr, run-with-lockfile: incorrect arguments\n);
usage(stderr);
return 101;
}
file= argv[1];
command = argv[2];
if (-1 == (fd = open(file, O_RDWR | O_CREAT, 0666))) {
fprintf(stderr, run-with-lockfile: %s: %s\n, file, strerror(errno));
return 101;
}
/* Paranoia. */
if (-1 == fstat(fd, st)) {
fprintf(stderr, run-with-lockfile: %s: %s\n, file, strerror(errno));
return 101;
} else if (!S_ISREG(st.st_mode)) {
fprintf(stderr, run-with-lockfile: %s: is not a regular file\n, file);
return 101;
}
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len= 0;
while (-1 == (n = fcntl(fd, wait ? F_SETLKW : F_SETLK, fl)) errno ==
EINTR);
if (n == -1) {
if (!wait (errno == EAGAIN || errno == EACCES))
return 100;
else {
fprintf(stderr, run-with-lockfile: %s: set lock: %s\n, file,
strerror(errno));
return 101;
}
}
/* Set an environment variable. */
envvar = malloc(strlen(file) + sizeof(LOCKFILE=));
sprintf(envvar, LOCKFILE=%s, file);
putenv(envvar);
errno = 0;
n = system(command);/* XXX should replace with fork/exec... */
if (n == -1) {
fprintf(stderr, run-with-lockfile: %s: %s\n, command,
strerror(errno));
n = 101;
} else if (n == 127 errno != 0) {
fprintf(stderr, run-with-lockfile: /bin/sh: %s\n, strerror(errno));
n = 101;
}
/* else n is the return code of the command... */
close(fd);
return n;
}
The shell script version look like this:
#!/bin/sh
# This shell script alternative to run-with-lockfile depends on the
# Debian package lockfile-progs (sudo apt-get install lockfile-progs)
# which uses liblockfile for NFS-safe locking.
# The locking strategy is not exactly the same as Chris Lightfoot's
# run-with-lockfile.c [1] but it should be substitutable in many
# circumstances, and in addition is NFS-safe.
# [1]
https://secure.mysociety.org/cvstrac/fileview?f=mysociety/run-with-lockfile/run-with-lockfile.c
FAIL_IF_OTHER=false
if [ x$1 = x-n ]
then
FAIL_IF_OTHER=true
shift
fi
if [ $# != 2 ]
then
echo Usage: $0 [-n] FILE COMMAND
exit 101
fi
LOCK_FILENAME=$1
COMMAND=$2
if [ $FAIL_IF_OTHER = true ] lockfile-check -l $LOCK_FILENAME
then
exit 100
fi
# This is based on the example in lockfile-progs(1):
lockfile-create -l $LOCK_FILENAME || exit 101
lockfile-touch -l $LOCK_FILENAME
#
