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Daniel Stenberg 2002-10-13 10:18:10 +00:00
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docs/libcurl/libcurl-multi.3
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@ -2,7 +2,7 @@
.\" nroff -man [file]
.\" $Id$
.\"
.TH libcurl-multi 5 "20 March 2001" "libcurl 7.9.5" "libcurl multi interface"
.TH libcurl-multi 5 "13 Oct 2001" "libcurl 7.10.1" "libcurl multi interface"
.SH NAME
libcurl-multi \- how to use the multi interface
.SH DESCRIPTION
@ -37,7 +37,7 @@ 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.
\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\fP (as when using the easy interface for transfers), you
@ -49,11 +49,11 @@ 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.
\fIcurl_easy_perform\fP on the handle 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
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\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
@ -62,24 +62,39 @@ 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
\fIcurl_multi_perform\fP like crazy. \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.
A little note here about the return codes from the multi functions, and
especially the \fIcurl_multi_perform\fP: if you receive
\fICURLM_CALL_MULTI_PERFORM\fP, this basicly means that you should call
\fIcurlm_call_multi_perform\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\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.
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\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.
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 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.
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 (possbily after having altered some options at your own choice).