1Implementation of the curl_multi_socket API 2 3 The main ideas of the new API are simply: 4 5 1 - The application can use whatever event system it likes as it gets info 6 from libcurl about what file descriptors libcurl waits for what action 7 on. (The previous API returns fd_sets which is very select()-centric). 8 9 2 - When the application discovers action on a single socket, it calls 10 libcurl and informs that there was action on this particular socket and 11 libcurl can then act on that socket/transfer only and not care about 12 any other transfers. (The previous API always had to scan through all 13 the existing transfers.) 14 15 The idea is that curl_multi_socket_action() calls a given callback with 16 information about what socket to wait for what action on, and the callback 17 only gets called if the status of that socket has changed. 18 19 We also added a timer callback that makes libcurl call the application when 20 the timeout value changes, and you set that with curl_multi_setopt() and the 21 CURLMOPT_TIMERFUNCTION option. To get this to work, Internally, there's an 22 added a struct to each easy handle in which we store an "expire time" (if 23 any). The structs are then "splay sorted" so that we can add and remove 24 times from the linked list and yet somewhat swiftly figure out both how long 25 time there is until the next nearest timer expires and which timer (handle) 26 we should take care of now. Of course, the upside of all this is that we get 27 a curl_multi_timeout() that should also work with old-style applications 28 that use curl_multi_perform(). 29 30 We created an internal "socket to easy handles" hash table that given 31 a socket (file descriptor) return the easy handle that waits for action on 32 that socket. This hash is made using the already existing hash code 33 (previously only used for the DNS cache). 34 35 To make libcurl able to report plain sockets in the socket callback, we had 36 to re-organize the internals of the curl_multi_fdset() etc so that the 37 conversion from sockets to fd_sets for that function is only done in the 38 last step before the data is returned. I also had to extend c-ares to get a 39 function that can return plain sockets, as that library too returned only 40 fd_sets and that is no longer good enough. The changes done to c-ares are 41 available in c-ares 1.3.1 and later. 42 43 We have done a test runs with up to 9000 connections (with a single active 44 one). The curl_multi_socket_action() invoke then takes less than 10 45 microseconds in average (using the read-only-1-byte-at-a-time hack). We are 46 now below the 60 microseconds "per socket action" goal (the extra 50 is the 47 time libevent needs). 48 49Documentation 50 51 http://curl.haxx.se/libcurl/c/curl_multi_socket_action.html 52 http://curl.haxx.se/libcurl/c/curl_multi_timeout.html 53 http://curl.haxx.se/libcurl/c/curl_multi_setopt.html 54