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#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <getopt.h>
#include <fcntl.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/types.h>
static const size_t M_SIZE = 1;
static bool use_fcntl = false;
static bool close_fd = true;
static bool should_wait = false;
static bool verbose = false;
static const char *path;
static bool parse_args (const int argc, const char **argv) {
int opt;
while ((opt = getopt(argc, (char *const*)argv, "fnwV")) != -1) {
switch (opt) {
case 'f': use_fcntl = true; break;
case 'n': close_fd = false; break;
case 'w': should_wait = true; break;
case 'V': verbose = true; break;
default: return false;
}
}
if (optind >= argc) {
return false;
}
else {
path = argv[optind];
}
return true;
}
int main (const int argc, const char **argv) {
int ec = 0;
int fd = -1;
int f_ret;
void *m = MAP_FAILED;
if (!parse_args(argc, argv)) {
ec = 2;
fprintf(stderr, "Usage: %s -fnw <lock file path>\n", argv[0]);
goto END;
}
if (!verbose) {
close(STDOUT_FILENO);
}
fd = open(path, O_CREAT | O_TRUNC | O_RDWR, 0755);
if (fd < 0) {
ec = 1;
perror(path);
goto END;
}
if (use_fcntl) {
struct flock fl;
memset(&fl, 0, sizeof(fl));
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_len = M_SIZE;
f_ret = fcntl(fd, F_SETLK, &fl);
}
else {
f_ret = flock(fd, LOCK_EX | LOCK_NB);
}
if (f_ret != 0) {
ec = 1;
perror(path);
goto END;
}
f_ret = ftruncate(fd, M_SIZE);
if (f_ret != 0) {
ec = 1;
perror(path);
goto END;
}
m = mmap(NULL, M_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (m == MAP_FAILED) {
ec = 1;
perror(path);
goto END;
}
// This block
if (close_fd) {
close(fd);
fd = -1;
}
printf("Lock holding\n");
if (should_wait) {
pause();
}
END:
if (fd >= 0) {
close(fd);
}
if (m != MAP_FAILED) {
munmap(m, M_SIZE);
}
return ec;
}
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