mirror of
https://github.com/moparisthebest/curl
synced 2024-12-23 00:28:48 -05:00
66 lines
3.6 KiB
Plaintext
66 lines
3.6 KiB
Plaintext
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.
|
|
|
|
In the API draft from before, we have a timeout argument on a per socket
|
|
basis and we also allowed curl_multi_socket_action() to pass in an 'easy
|
|
handle' instead of socket to allow libcurl to shortcut a lookup and work on
|
|
the affected easy handle right away. Both these turned out to be bad ideas.
|
|
|
|
The timeout argument was removed from the socket callback since after much
|
|
thinking I came to the conclusion that we really don't want to handle
|
|
timeouts on a per socket basis. We need it on a per transfer (easy handle)
|
|
basis and thus we can't provide it in the callbacks in a nice way. Instead,
|
|
we have to offer a curl_multi_timeout() that returns the largest amount of
|
|
time we should wait before we call the "timeout action" of libcurl, to
|
|
trigger the proper internal timeout action on the affected transfer. To get
|
|
this to work, I 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 1 - how long time there is until the next timer expires and 2 - which
|
|
timer (handle) should we 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 also added a timer callback that makes libcurl call the application when
|
|
the timeout value changes, and you set that with curl_multi_setopt().
|
|
|
|
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
|