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