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