linux 创建 pidfile 程序

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>

static char *saved_pidfile;

static void pidfile_delete(void)
{
        if (saved_pidfile) unlink(saved_pidfile);
}

int pidfile_acquire(const char *pidfile)
{
        int pid_fd;
        if (!pidfile) return -1;

        pid_fd = open(pidfile, O_CREAT | O_WRONLY, 0644);
        if (pid_fd < 0) {
                printf("Unable to open pidfile %s: %m\n", pidfile);
        } else {
                lockf(pid_fd, F_LOCK, 0);
                if (!saved_pidfile)
                        atexit(pidfile_delete);
                saved_pidfile = (char *) pidfile;
        }
        return pid_fd;
}

void pidfile_write_release(int pid_fd)
{
        FILE *out;

        if (pid_fd < 0) return;

        if ((out = fdopen(pid_fd, "w")) != NULL) {
                fprintf(out, "%d\n", getpid());
                fclose(out);
        }
        lockf(pid_fd, F_UNLCK, 0);
        close(pid_fd);
}

void create_pidfile(void)
{
        int fd;
        fd = pidfile_acquire("/var/run/gpio.pid");
        pidfile_write_release(fd);
}

int main(int argc, char *argv[])
{
        create_pidfile();
        return 0;
}