protected IRubyObject rbIoClose(ThreadContext context) {
        OpenFile fptr;
        RubyIO write_io;
        OpenFile write_fptr;

        write_io = GetWriteIO();
        if (this != write_io) {
            write_fptr = write_io.openFile;

            boolean locked = write_fptr.lock();
            try {
                if (write_fptr != null && write_fptr.fd() != null) {
                    write_fptr.cleanup(context.runtime, true);
                }
            } finally {
                if (locked) write_fptr.unlock();
            }
        }

        fptr = openFile;

        boolean locked = fptr.lock();
        try {
            if (fptr == null) return context.nil;
            if (fptr.fd() == null) return context.nil;
            final Ruby runtime = context.runtime;
...
        } finally {
            if (locked) fptr.unlock();
        }

        return context.nil;
    }