如何在Libevent中修改注册事件？

Question

I use libevent like this,

client->m_event = event_new(listener->m_server->m_server_base, client->m_sockfd, EV_PERSIST, Client::ClientEventCallback, client);
event_add(client->m_event, NULL);

But I don't know how to modify the event of m_event, there seems to be no interface to operate in official manual, i tried to do it like this, but it make a core dump.

short event = event_get_events(m_event);
event_del(m_event);
event_assign(m_event, m_server->m_server_base, m_sockfd, event | EV_WRITE, Client::ClientEventCallback, this);
event_add(m_event, NULL); 

core dump ocurs at event_assign, please help me ... how to modify the registed event of the struct event ?

Answer 1

I don't see anything in your code that should make you core dump, but I might inquire as to why you're event_assign'ing again anyways just to add in the EV_WRITE flag. Correct me if i'm wrong, but since your event_new is only specifying EV_PERSIST , I don't think it'll ever fire (so why event_add it at that point?) It seems like you should just be doing

client->m_event = event_new(listener->m_server->m_server_base, client->m_sockfd, EV_PERSIST | EV_WRITE, Client::ClientEventCallback, client);

up top, then when you are ready to write just do

event_add(m_event, NULL);

and when you're done writing

event_del(m_event);

Anyways, like I said I wouldn't think what you're doing should be a problem per-say, but if there is some funky behavior that happens when you add an event with only EV_PERSIST as the event type and then later del/assign it, the above may solve it. (And it'll be less code / more effecient anyways, so might as well :))