Now there is still a problem.
When I DO added the second parameter to the code, it still gives me the error notice of "send_packet(GEARMAN_COULD_NOT_CONNECT)".
At first, I thought it was the problem of my code, so I tested another piece of code which isn't changed by me, and it is also the code sample which I ran for testing gearman. However, it still failed. Any help?