NAME
curl_multi_fdset - extracts file descriptor information from a multi
handle
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_fdset(CURLM *multi_handle,
fd_set *read_fd_set,
fd_set *write_fd_set,
fd_set *exc_fd_set,
int *max_fd);
DESCRIPTION
This function extracts file descriptor information from a given
multi_handle. libcurl returns its fd_set sets. The application can use
these to select() on, but be sure to FD_ZERO them before calling this
function as curl_multi_fdset(3) only adds its own descriptors, it
doesn’t zero or otherwise remove any others. The curl_multi_perform(3)
function should be called as soon as one of them is ready to be read
from or written to.
To be sure to have up-to-date results, you should call
curl_multi_perform until it does not return CURLM_CALL_MULTI_PERFORM
prior to calling curl_multi_fdset. This will make sure that libcurl
has updated the handles’ socket states.
If no file descriptors are set by libcurl, max_fd will contain -1 when
this function returns. Otherwise it will contain the higher descriptor
number libcurl set.
When doing select(), you should use curl_multi_timeout to figure out
how long to wait for action. Call curl_multi_perform even if no
activity has been seen on the fd_sets after the timeout expires as
otherwise internal retries and timeouts may not work as you’d think and
want.
RETURN VALUE
CURLMcode type, general libcurl multi interface error code. See
libcurl-errors(3)
SEE ALSO
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_timeout(3),
curl_multi_perform(3)