-.\"
+.\" **************************************************************************
+.\" * _ _ ____ _
+.\" * Project ___| | | | _ \| |
+.\" * / __| | | | |_) | |
+.\" * | (__| |_| | _ <| |___
+.\" * \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2014, 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
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.
+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 the \fIread_fd_set\fP argument is not a null pointer, it points to an
+object of type fd_set that on returns specifies the file descriptors to be
+checked for being ready to read.
+
+If the \fIwrite_fd_set\fP argument is not a null pointer, it points to an
+object of type fd_set that on return specifies the file descriptors to be
+checked for being ready to write.
+
+If the \fIexc_fd_set\fP argument is not a null pointer, it points to an object
+of type fd_set that on return specifies the file descriptors to be checked for
+error conditions pending.
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.
+this function returns. Otherwise it will contain the highest 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(). You then need to wait a while before you
+proceed and call \fIcurl_multi_perform(3)\fP anyway. How long to wait? We
+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 \fIcurl_multi_timeout(3)\fP to figure out
+how long to wait for action. Call \fIcurl_multi_perform(3)\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.
-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. 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) "
+.BR curl_multi_wait "(3), "
+.BR curl_multi_timeout "(3), " curl_multi_perform "(3), " select "(2) "
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