On Fri, 5 May 2017, Pahome Chen via curl-library wrote:

> curl_multi_socket_action(CURLM * multi_handle,
> *curl_socket_t sockfd*,
> int ev_bitmask,
> int *running_handles);
>
> It always said that we can set to the socket *sockfd *with *action*, it
> doesn't mentioned what's the functionality of *sockfd *in the function.That
> makes me confused.

It is mentioned in several places in the documentation, and I've explained it
in previous replies. But let me try again.

curl_multi_socket_action is part of the multi_socket API. It is an event-based
API. It assumes that you use an event-based library or underlying system that
tells you when there's activity/action on one of the sockets/file descriptors
you've asked it to monitor.

When you use curl_multi_socket_action(), you get told by libcurl which file
descriptors to wait for and for what particular activity on that socket. You
should then set that information in your event-based library.

Then, when your event-lib tells you there actually is actitity on the socket
that it monitors on the behalf of libcurl, it probably calls a callback you
have provided for it.

You then call curl_multi_socket_action() to tell libcurl about which socket
that got action and what particular action it was that was detected. That
socket is the 'sockfd' argument to curl_multi_socket_action() and 'ev_bitmask'
is what activity/events that happened on the socket.

-- 
  / daniel.haxx.se
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