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#include 

struct flock* file_lock(int type, int whence) {
    static struct flock ret ;
    ret.l_type = type ;
    ret.l_start = 0 ;
    ret.l_whence = whence ;
    ret.l_len = 0 ;
    ret.l_pid = getpid() ;
    return &ret ;
}

read_lock(FILE *f) {   /* a shared lock on an entire file */

    fcntl(fileno(f), F_SETLKW, file_lock(F_RDLCK, SEEK_SET));
}

write_lock(FILE *f) {  /* an exclusive lock on an entire file */

    fcntl(fileno(f), F_SETLKW, file_lock(F_WRLCK, SEEK_SET));
}

append_lock(FILE *f) { /* a lock on the _end_ of a file -- other
                       processes may access existing records */

    fcntl(fileno(f), F_SETLKW, file_lock(F_WRLCK, SEEK_END));
}

un_lock(FILE *f) { /* ulock an entire file */
  fcntl(fileno(f), F_SETLKW, file_lock(F_UNLCK, SEEK_SET));
}