docs/libcurl/libcurl-multi.3 - third_party/curl - Git at Google

 .\" You can view this file with:
 .\" nroff -man [file]
 .\" $Id$
 .\"
 .TH libcurl-multi 5 "20 March 2001" "libcurl 7.9.5" "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 libcurl-the-guide document for a complete tutorial to
 programming with libcurl and the \fIlibcurl(3)\fP man page for an overview of
 the libcurl easy interface.

 All functions in the multi interface are prefixed with curl_multi.
 .SH "PLEASE NOTICE"
 The multi interface is a rather new member of the libcurl family. It has not
 yet been very widely used. It may still be a few more bugs lurking in there
 than we are used to. That said, it might also just work in every aspect you
 try it. Please report all bugs and oddities you see.
 .SH "OBJECTIVES"
 The multi interface introduces several new abilities that the easy interface
 refuses to offer. 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 select() 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\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.

 When the easy handle is setup for a transfer, then instead of using
 \fIcurl_easy_perform\fP (as when using the easy interface for transfers), you
 should instead add the easy handle to the multi handle using
 \fIcurl_easy_add_handl\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\fP. Once removed from the multi
 handle, you can again use other easy interface functions like
 curl_easy_perform or whatever you think is necessary.

 Adding the easy handles to the multi handle does not start any
 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\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\fP like a mad man! \fIcurl_multi_fdset\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\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.

 To get information about completed transfers, to figure out success or not and
 similar, \fIcurl_multi_info_read\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.

 When all transfers in the multi stack are done, cleanup the multi handle with
 \fIcurl_multi_cleanup\fP. Be careful and please note that you \fBMUST\fP
 invoke separate \fIcurl_easy_cleanup\fP calls on every single easy handle to
 clean them up properly.
	.\" You can view this file with:
	.\" nroff -man [file]
	.\" $Id$
	.\"
	.TH libcurl-multi 5 "20 March 2001" "libcurl 7.9.5" "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 libcurl-the-guide document for a complete tutorial to
	programming with libcurl and the \fIlibcurl(3)\fP man page for an overview of
	the libcurl easy interface.

	All functions in the multi interface are prefixed with curl_multi.
	.SH "PLEASE NOTICE"
	The multi interface is a rather new member of the libcurl family. It has not
	yet been very widely used. It may still be a few more bugs lurking in there
	than we are used to. That said, it might also just work in every aspect you
	try it. Please report all bugs and oddities you see.
	.SH "OBJECTIVES"
	The multi interface introduces several new abilities that the easy interface
	refuses to offer. 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 select() 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\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.

	When the easy handle is setup for a transfer, then instead of using
	\fIcurl_easy_perform\fP (as when using the easy interface for transfers), you
	should instead add the easy handle to the multi handle using
	\fIcurl_easy_add_handl\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\fP. Once removed from the multi
	handle, you can again use other easy interface functions like
	curl_easy_perform or whatever you think is necessary.

	Adding the easy handles to the multi handle does not start any
	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\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\fP like a mad man! \fIcurl_multi_fdset\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\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.

	To get information about completed transfers, to figure out success or not and
	similar, \fIcurl_multi_info_read\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.

	When all transfers in the multi stack are done, cleanup the multi handle with
	\fIcurl_multi_cleanup\fP. Be careful and please note that you \fBMUST\fP
	invoke separate \fIcurl_easy_cleanup\fP calls on every single easy handle to
	clean them up properly.