curl_multi_fdset(3)

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)