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diff --git a/docs/libcurl/libcurl-multi.3 b/docs/libcurl/libcurl-multi.3 new file mode 100644 index 000000000..a07736de2 --- /dev/null +++ b/docs/libcurl/libcurl-multi.3 @@ -0,0 +1,80 @@ +.\" You can view this file with: +.\" nroff -man [file] +.\" $Id$ +.\" +.TH libcurl-multi 5 "19 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 "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. |