I use this producer example to send transaction message to RocketMQ, why the check_callback callback function cannot execute?

1. Please describe the issue you observed:
I use this producer example to send transaction message to RocketMQ, why the check_callback callback function cannot execute?

2. Please tell us about your environment:

mac os

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):

```
def send_transaction_message(count):
producer = TransactionMQProducer(gid, check_callback)
producer.set_name_server_address(name_srv)
producer.start()
for n in range(count):
msg = create_message()
ret = producer.send_message_in_transaction(msg, local_execute, None)
print ('send message status: ' + str(ret.status) + ' msgId: ' + ret.msg_id)
print ('send transaction message done')

while True:
time.sleep(3600)
```