mingw/share/man/man3/libcurl-multi.3 - external/msysgit/msysgit - Git at Google

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 .\" *                                  _   _ ____  _
 .\" *  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 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.

 \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"
 \fIcurl_multi_socket_action(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-performance API that will make a significant difference for applications
 using large numbers of simultaneous connections.

 \fIcurl_multi_socket_action(3)\fP is then used instead of
 \fIcurl_multi_perform(3)\fP.

 When using this API, you add easy handles to the multi handle just as with the
 normal multi interface. Then you also set two callbacks with the
 CURLMOPT_SOCKETFUNCTION and CURLMOPT_TIMERFUNCTION options to
 \fIcurl_multi_setopt(3)\fP.

 The API is then designed to inform your application about which sockets
 libcurl is currently using and for what activities (read and/or write) on
 those sockets your application is expected to wait for.

 Your application must then make sure to receive all sockets informed about in
 the CURLMOPT_SOCKETFUNCTION callback and make sure it reacts on the given
 activity on them. When a socket has the given activity, you call
 \fIcurl_multi_socket_action(3)\fP specifying which socket and action there
 are.

 The CURLMOPT_TIMERFUNCTION callback is called to set a timeout. When that
 timeout expires, your application should call the
 \fIcurl_multi_socket_action(3)\fP function saying it was due to a timeout.
 .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 unless the c-ares or threaded-resolver backends are used
  - NSS SSL connections
  - HTTP proxy CONNECT operations
  - SOCKS proxy handshakes
  - file:// transfers
  - TELNET transfers
 .fi
	.\" **************************************************************************
	.\" * _ _ ____ _
	.\" * 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 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.

	\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"
	\fIcurl_multi_socket_action(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-performance API that will make a significant difference for applications
	using large numbers of simultaneous connections.

	\fIcurl_multi_socket_action(3)\fP is then used instead of
	\fIcurl_multi_perform(3)\fP.

	When using this API, you add easy handles to the multi handle just as with the
	normal multi interface. Then you also set two callbacks with the
	CURLMOPT_SOCKETFUNCTION and CURLMOPT_TIMERFUNCTION options to
	\fIcurl_multi_setopt(3)\fP.

	The API is then designed to inform your application about which sockets
	libcurl is currently using and for what activities (read and/or write) on
	those sockets your application is expected to wait for.

	Your application must then make sure to receive all sockets informed about in
	the CURLMOPT_SOCKETFUNCTION callback and make sure it reacts on the given
	activity on them. When a socket has the given activity, you call
	\fIcurl_multi_socket_action(3)\fP specifying which socket and action there
	are.

	The CURLMOPT_TIMERFUNCTION callback is called to set a timeout. When that
	timeout expires, your application should call the
	\fIcurl_multi_socket_action(3)\fP function saying it was due to a timeout.
	.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 unless the c-ares or threaded-resolver backends are used
	- NSS SSL connections
	- HTTP proxy CONNECT operations
	- SOCKS proxy handshakes
	- file:// transfers
	- TELNET transfers
	.fi