Hi everyone- A little background: my name is Jason Sobel, I'm an infrastructure engineer at Facebook and I'm looking at using evhttp as the backbone for Facebook's custom HTTP servers. I am currently working on two specific projects and we'll almost certainly end up writing more down the road so this server is something that will see a lot of use.
I know libevent & threaded applications has been discussed before, with the prevailing wisdom provided by fellow Facebook engineer Steven Grimm: http://monkeymail.org/archives/libevent-users/2007-January/000450.html I've been reading over the evhttp code recently (1.4.1-beta) and, from what I can see, the approach Steve describes will not work for evhttp. The problem appears to be that, once a connection is created, the event base cannot be changed. Thus all connection are trapped on the same event base and you can't hand them off to other threads to complete. The only workaround I've found is to hand out some work to a thread, have it put completed requests on a thread-safe queue, and rely on an evtimer to periodically complete all the requests on that queue. Can anyone out there confirm that I'm understanding the code correctly? I've been toying with an idea for changing the code to more readily support multiple threads, however, and was hoping to get some feedback. The basic idea is to change accept_socket: static void accept_socket(int fd, short what, void *arg) { struct evhttp *http = arg; struct sockaddr_storage ss; socklen_t addrlen = sizeof(ss); int nfd; if ((nfd = accept(fd, (struct sockaddr *)&ss, &addrlen)) == -1) { event_warn("%s: bad accept", __func__); return; } if (evutil_make_socket_nonblocking(nfd) < 0) return; evhttp_get_request(http, nfd, (struct sockaddr *)&ss, addrlen); } Instead of accepting a single evhttp instance my idea is to pass in a variable number of evhttp structures, each with a different event base. When calling evhttp_get_request I would somehow (randomly, round-robin, user-defined, etc.) choose a evhttp to pass on. I *think* that this change will correctly trickle down throughout the rest of the code and allow multiple connections to run in parallel on different event bases. Thanks for taking the time to look over this, I hope to get feedback/comments! --jason _______________________________________________ Libevent-users mailing list Libevent-users@monkey.org http://monkeymail.org/mailman/listinfo/libevent-users
