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+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2007, 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.
+.\" *
+.\" * $Id$
+.\" **************************************************************************
+.\"
+.TH libcurl-multi 3 "3 Feb 2007" "libcurl 7.16.0" "libcurl multi interface"
+.SH NAME
+libcurl-multi \- how to use the multi interface
+.SH DESCRIPTION
+This is an overview on how to use the libcurl multi interface in your C
+programs. There are specific man pages for each function mentioned in
+here. There's also the \fIlibcurl-tutorial(3)\fP man page for a complete
+tutorial to programming with libcurl and the \fIlibcurl-easy(3)\fP man page
+for an overview of the libcurl easy interface.
+
+All functions in the multi interface are prefixed with curl_multi.
+.SH "OBJECTIVES"
+The multi interface offers several abilities that the easy interface doesn't.
+They are mainly:
+
+1. Enable a "pull" interface. The application that uses libcurl decides where
+and when to ask libcurl to get/send data.
+
+2. Enable multiple simultaneous transfers in the same thread without making it
+complicated for the application.
+
+3. Enable the application to wait for action on its own file descriptors and
+curl's file descriptors simultaneous easily.
+.SH "ONE MULTI HANDLE MANY EASY HANDLES"
+To use the multi interface, you must first create a 'multi handle' with
+\fIcurl_multi_init(3)\fP. This handle is then used as input to all further
+curl_multi_* functions.
+
+Each single transfer is built up with an easy handle. You must create them,
+and setup the appropriate options for each easy handle, as outlined in the
+\fIlibcurl(3)\fP man page, using \fIcurl_easy_setopt(3)\fP.
+
+When the easy handle is setup for a transfer, then instead of using
+\fIcurl_easy_perform(3)\fP (as when using the easy interface for transfers),
+you should instead add the easy handle to the multi handle using
+\fIcurl_multi_add_handle(3)\fP. The multi handle is sometimes referred to as a
+\'multi stack\' because of the fact that it may hold a large amount of easy
+handles.
+
+Should you change your mind, the easy handle is again removed from the multi
+stack using \fIcurl_multi_remove_handle(3)\fP. Once removed from the multi
+handle, you can again use other easy interface functions like
+\fIcurl_easy_perform(3)\fP on the handle or whatever you think is necessary.
+
+Adding the easy handle to the multi handle does not start the transfer.
+Remember that one of the main ideas with this interface is to let your
+application drive. You drive the transfers by invoking
+\fIcurl_multi_perform(3)\fP. libcurl will then transfer data if there is
+anything available to transfer. It'll use the callbacks and everything else
+you have setup in the individual easy handles. It'll transfer data on all
+current transfers in the multi stack that are ready to transfer anything. It
+may be all, it may be none.
+
+Your application can acquire knowledge from libcurl when it would like to get
+invoked to transfer data, so that you don't have to busy-loop and call that
+\fIcurl_multi_perform(3)\fP like crazy. \fIcurl_multi_fdset(3)\fP offers an
+interface using which you can extract fd_sets from libcurl to use in select()
+or poll() calls in order to get to know when the transfers in the multi stack
+might need attention. This also makes it very easy for your program to wait
+for input on your own private file descriptors at the same time or perhaps
+timeout every now and then, should you want that.
+
+A little note here about the return codes from the multi functions, and
+especially the \fIcurl_multi_perform(3)\fP: if you receive
+\fICURLM_CALL_MULTI_PERFORM\fP, this basically means that you should call
+\fIcurl_multi_perform(3)\fP again, before you select() on more actions. You
+don't have to do it immediately, but the return code means that libcurl may
+have more data available to return or that there may be more data to send off
+before it is "satisfied".
+
+\fIcurl_multi_perform(3)\fP stores the number of still running transfers in
+one of its input arguments, and by reading that you can figure out when all
+the transfers in the multi handles are done. 'done' does not mean
+successful. One or more of the transfers may have failed. Tracking when this
+number changes, you know when one or more transfers are done.
+
+To get information about completed transfers, to figure out success or not and
+similar, \fIcurl_multi_info_read(3)\fP should be called. It can return a
+message about a current or previous transfer. Repeated invokes of the function
+get more messages until the message queue is empty. The information you
+receive there includes an easy handle pointer which you may use to identify
+which easy handle the information regards.
+
+When a single transfer is completed, the easy handle is still left added to
+the multi stack. You need to first remove the easy handle with
+\fIcurl_multi_remove_handle(3)\fP and then close it with
+\fIcurl_easy_cleanup(3)\fP, or possibly set new options to it and add it again
+with \fIcurl_multi_add_handle(3)\fP to start another transfer.
+
+When all transfers in the multi stack are done, cleanup the multi handle with
+\fIcurl_multi_cleanup(3)\fP. Be careful and please note that you \fBMUST\fP
+invoke separate \fIcurl_easy_cleanup(3)\fP calls on every single easy handle
+to clean them up properly.
+
+If you want to re-use an easy handle that was added to the multi handle for
+transfer, you must first remove it from the multi stack and then re-add it
+again (possibly after having altered some options at your own choice).
+.SH "MULTI_SOCKET"
+Since 7.16.0, the \fIcurl_multi_socket(3)\fP function offers a way for
+applications to not only avoid being forced to use select(), but it also
+offers a much more high-performing API that will make a significant difference
+for applications using large numbers of simultaneous connections.
+
+\fIcurl_multi_socket(3)\fP (and \fIcurl_multi_socket_all(3)\fP) is then used
+instead of \fIcurl_multi_perform(3)\fP.
+.SH "BLOCKING"
+A few areas in the code are still using blocking code, even when used from the
+multi interface. While we certainly want and intend for these to get fixed in
+the future, you should be aware of the following current restrictions:
+
+.nf
+ - Name resolves on non-windows unless c-ares is used
+ - GnuTLS SSL connections
+ - Active FTP connections
+ - HTTP proxy CONNECT operations
+ - TFTP transfers
+ - file:// transfers
+.fi