In reply to jundijiujieke:
Unfortunately the code you are providing is confusing.
After your last post I assume req is a variable of your seq_item.
In the previous post you are doing
seq_item_port.get_next_item(req);
drive_one_pkt(req);
This indicates req is a seq_item.
Is it possibel to share your code on EDAPlaygound.com
or privately with me, sending your code to christoph@christoph-suehnel.de.