curl/docs/libcurl/curl_multi_fdset.3

.\" $Id$
.\"
.TH curl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_fdset - extracts file descriptor information from a multi handle
.SH SYNOPSIS
.nf
#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);
.ad
.SH 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
\fIcurl_multi_fdset(3)\fP only adds its own descriptors, it doesn't zero or
otherwise remove any others. The \fIcurl_multi_perform(3)\fP 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
\fIcurl_multi_perform\fP until it does not return CURLM_CALL_MULTI_PERFORM
prior to calling \fIcurl_multi_fdset\fP.  This will make sure that libcurl has
updated the handles' socket states.

If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when
this function returns. Otherwise it will contain the higher descriptor number
libcurl set.

You should also be aware that when doing select(), you should consider using a
rather small (single-digit number of seconds) timeout and call
\fIcurl_multi_perform\fP regularly - even if no activity has been seen on the
fd_sets - as otherwise libcurl-internal retries and timeouts may not work as
you'd think and want.

Starting with libcurl 7.16.0, you should use \fBcurl_multi_timeout\fP to
figure out how long to wait for action.
.SH RETURN VALUE
CURLMcode type, general libcurl multi interface error code. See
\fIlibcurl-errors(3)\fP
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_timeout "(3), " curl_multi_perform "(3) "