-.\" $Id$
-.\"
-.TH curl_multi_fdset 3 "3 May 2002" "libcurl 7.9.5" "libcurl Manual"
+.\" **************************************************************************
+.\" * _ _ ____ _
+.\" * Project ___| | | | _ \| |
+.\" * / __| | | | |_) | |
+.\" * | (__| |_| | _ <| |___
+.\" * \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at http://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.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,
.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() or
-poll() on. The curl_multi_perform() function should be called as soon as one
-of them are ready to be read from or written to.
+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.
-NOTE that once this call is made, you must not remove the sets you point to,
-as libcurl will need to be able to read them. It needs them after select()
-calls, to know if certain sockets are readable or writable.
+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. When libcurl returns -1 in \fImax_fd\fP, it is because libcurl
+currently does something that isn't possible for your application to monitor
+with a socket and unfortunately you can then not know exactly when the current
+action is completed using select(). When max_fd returns with -1, you need to
+wait a while and then proceed and call \fIcurl_multi_perform\fP anyway. How
+long to wait? I would suggest 100 milliseconds at least, but you may want to
+test it out in your own particular conditions to find a suitable value.
+
+When doing select(), you should use \fBcurl_multi_timeout\fP to figure out how
+long to wait for action. Call \fIcurl_multi_perform\fP 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.
+
+If one of the sockets used by libcurl happens to be larger than what can be
+set in an fd_set, which on POSIX systems means that the file descriptor is
+larger than FD_SETSIZE, then libcurl will try to not set it. Setting a too
+large file descriptor in an fd_set implies an out of bounds write which can
+cause crashes, or worse. The effect of NOT storing it will possibly save you
+from the crash, but will make your program NOT wait for sockets it should wait
+for...
.SH RETURN VALUE
-CURLMcode type, general libcurl multi interface error code.
+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_cleanup "(3), " curl_multi_init "(3), "
+.BR curl_multi_timeout "(3), " curl_multi_perform "(3) "
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