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Linux flock(2) 2.22.1 with some minor changes for compiling on OSX. I have not run any test but basic functionality works.

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flock_osx.c
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/* Copyright 2003-2005 H. Peter Anvin - All Rights Reserved
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom
* the Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall
* be included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
 
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <paths.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
 
#include "c.h"
#include "nls.h"
#include "strutils.h"
#include "closestream.h"
 
static void __attribute__((__noreturn__)) usage(int ex)
{
fprintf(stderr, USAGE_HEADER);
fprintf(stderr,
_(" %1$s [options] <file descriptor number>\n"
" %1$s [options] <file> -c <command>\n"
" %1$s [options} <directory> -c <command>\n"),
program_invocation_short_name);
fputs(USAGE_OPTIONS, stderr);
fputs(_( " -s --shared get a shared lock\n"), stderr);
fputs(_( " -x --exclusive get an exclusive lock (default)\n"), stderr);
fputs(_( " -u --unlock remove a lock\n"), stderr);
fputs(_( " -n --nonblock fail rather than wait\n"), stderr);
fputs(_( " -w --timeout <secs> wait for a limited amount of time\n"), stderr);
fputs(_( " -E --conflict-exit-code <number> exit code after conflict or timeout\n"), stderr);
fputs(_( " -o --close close file descriptor before running command\n"), stderr);
fputs(_( " -c --command <command> run a single command string through the shell\n"), stderr);
fprintf(stderr, USAGE_SEPARATOR);
fprintf(stderr, USAGE_HELP);
fprintf(stderr, USAGE_VERSION);
fprintf(stderr, USAGE_MAN_TAIL("flock(1)"));
exit(ex);
}
 
static sig_atomic_t timeout_expired = 0;
 
static void timeout_handler(int sig __attribute__((__unused__)))
{
timeout_expired = 1;
}
 
static void strtotimeval(const char *str, struct timeval *tv)
{
double user_input;
 
user_input = strtod(str, NULL);
tv->tv_sec = (time_t) user_input;
tv->tv_usec = (long)((user_input - tv->tv_sec) * 1000000);
if ((tv->tv_sec + tv->tv_usec) == 0)
errx(EX_USAGE, _("timeout cannot be zero"));
}
 
static void setup_timer(struct itimerval *timer, struct itimerval *old_timer,
struct sigaction *sa, struct sigaction *old_sa)
{
memset(sa, 0, sizeof *sa);
sa->sa_handler = timeout_handler;
sa->sa_flags = SA_RESETHAND;
sigaction(SIGALRM, sa, old_sa);
setitimer(ITIMER_REAL, timer, old_timer);
}
 
static void cancel_timer(struct itimerval *old_timer, struct sigaction *old_sa)
{
setitimer(ITIMER_REAL, old_timer, NULL);
sigaction(SIGALRM, old_sa, NULL);
}
 
static int open_file(const char *filename, int *flags)
{
 
int fd;
int fl = *flags == 0 ? O_RDONLY : *flags;
 
errno = 0;
fl |= O_NOCTTY | O_CREAT;
fd = open(filename, fl, 0666);
 
/* Linux doesn't like O_CREAT on a directory, even though it
* should be a no-op; POSIX doesn't allow O_RDWR or O_WRONLY
*/
if (fd < 0 && errno == EISDIR) {
fl = O_RDONLY | O_NOCTTY;
fd = open(filename, fl);
}
if (fd < 0) {
warn(_("cannot open lock file %s"), filename);
if (errno == ENOMEM || errno == EMFILE || errno == ENFILE)
exit(EX_OSERR);
if (errno == EROFS || errno == ENOSPC)
exit(EX_CANTCREAT);
exit(EX_NOINPUT);
}
*flags = fl;
return fd;
}
 
int main(int argc, char *argv[])
{
struct itimerval timeout, old_timer;
int have_timeout = 0;
int type = LOCK_EX;
int block = 0;
int open_flags = 0;
int fd = -1;
int opt, ix;
int do_close = 0;
int status;
/*
* The default exit code for lock conflict or timeout
* is specified in man flock.1
*/
int conflict_exit_code = 1;
char **cmd_argv = NULL, *sh_c_argv[4];
const char *filename = NULL;
struct sigaction sa, old_sa;
 
static const struct option long_options[] = {
{"shared", no_argument, NULL, 's'},
{"exclusive", no_argument, NULL, 'x'},
{"unlock", no_argument, NULL, 'u'},
{"nonblocking", no_argument, NULL, 'n'},
{"nb", no_argument, NULL, 'n'},
{"timeout", required_argument, NULL, 'w'},
{"wait", required_argument, NULL, 'w'},
{"conflict-exit-code", required_argument, NULL, 'E'},
{"close", no_argument, NULL, 'o'},
{"help", no_argument, NULL, 'h'},
{"version", no_argument, NULL, 'V'},
{NULL, 0, NULL, 0}
};
 
setlocale(LC_ALL, "");
bindtextdomain(PACKAGE, LOCALEDIR);
textdomain(PACKAGE);
atexit(close_stdout);
 
if (argc < 2)
usage(EX_USAGE);
 
memset(&timeout, 0, sizeof timeout);
 
optopt = 0;
while ((opt =
getopt_long(argc, argv, "+sexnouw:E:hV?", long_options,
&ix)) != EOF) {
switch (opt) {
case 's':
type = LOCK_SH;
break;
case 'e':
case 'x':
type = LOCK_EX;
break;
case 'u':
type = LOCK_UN;
break;
case 'o':
do_close = 1;
break;
case 'n':
block = LOCK_NB;
break;
case 'w':
have_timeout = 1;
strtotimeval(optarg, &timeout.it_value);
break;
case 'E':
conflict_exit_code = strtol(optarg, NULL, 10);
break;
case 'V':
printf("flock (%s)\n", "2.22.1");//PACKAGE_STRING);
exit(EX_OK);
default:
/* optopt will be set if this was an unrecognized
* option, i.e. *not* 'h' or '?
*/
usage(optopt ? EX_USAGE : 0);
break;
}
}
 
if (argc > optind + 1) {
/* Run command */
if (!strcmp(argv[optind + 1], "-c") ||
!strcmp(argv[optind + 1], "--command")) {
if (argc != optind + 3)
errx(EX_USAGE,
_("%s requires exactly one command argument"),
argv[optind + 1]);
cmd_argv = sh_c_argv;
cmd_argv[0] = getenv("SHELL");
if (!cmd_argv[0] || !*cmd_argv[0])
cmd_argv[0] = _PATH_BSHELL;
cmd_argv[1] = "-c";
cmd_argv[2] = argv[optind + 2];
cmd_argv[3] = 0;
} else {
cmd_argv = &argv[optind + 1];
}
 
filename = argv[optind];
fd = open_file(filename, &open_flags);
 
} else if (optind < argc) {
/* Use provided file descriptor */
fd = (int)strtol(argv[optind], NULL, 10);
} else {
/* Bad options */
errx(EX_USAGE, _("requires file descriptor, file or directory"));
}
 
if (have_timeout) {
if (timeout.it_value.tv_sec == 0 &&
timeout.it_value.tv_usec == 0) {
/* -w 0 is equivalent to -n; this has to be
* special-cased because setting an itimer to zero
* means disabled!
*/
have_timeout = 0;
block = LOCK_NB;
} else
setup_timer(&timeout, &old_timer, &sa, &old_sa);
}
 
while (flock(fd, type | block)) {
switch (errno) {
case EWOULDBLOCK:
/* -n option set and failed to lock. */
exit(conflict_exit_code);
case EINTR:
/* Signal received */
if (timeout_expired)
/* -w option set and failed to lock. */
exit(conflict_exit_code);
/* otherwise try again */
continue;
case EIO:
/* Probably NFSv4 where flock() is emulated by fcntl().
* Let's try to reopen in read-write mode.
*/
if (!(open_flags & O_RDWR) &&
type != LOCK_SH &&
access(filename, R_OK | W_OK) == 0) {
 
close(fd);
open_flags = O_RDWR;
fd = open_file(filename, &open_flags);
 
if (open_flags & O_RDWR)
break;
}
/* go through */
default:
/* Other errors */
if (filename)
warn("%s", filename);
else
warn("%d", fd);
exit((errno == ENOLCK
|| errno == ENOMEM) ? EX_OSERR : EX_DATAERR);
}
}
 
if (have_timeout)
cancel_timer(&old_timer, &old_sa);
 
status = EX_OK;
 
if (cmd_argv) {
pid_t w, f;
/* Clear any inherited settings */
signal(SIGCHLD, SIG_DFL);
f = fork();
 
if (f < 0) {
err(EX_OSERR, _("fork failed"));
} else if (f == 0) {
if (do_close)
close(fd);
execvp(cmd_argv[0], cmd_argv);
/* execvp() failed */
warn("%s", cmd_argv[0]);
_exit((errno == ENOMEM) ? EX_OSERR : EX_UNAVAILABLE);
} else {
do {
w = waitpid(f, &status, 0);
if (w == -1 && errno != EINTR)
break;
} while (w != f);
 
if (w == -1) {
status = EXIT_FAILURE;
warn(_("waitpid failed"));
} else if (WIFEXITED(status))
status = WEXITSTATUS(status);
else if (WIFSIGNALED(status))
status = WTERMSIG(status) + 128;
else
/* WTF? */
status = EX_OSERR;
}
}
 
return status;
}

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