NAME
curl_multi_perform - reads/writes available data from each easy handle
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);
DESCRIPTION
When the app thinks there's data available for the multi_handle, it should
call this function to read/write whatever there is to read or write right
now. curl_multi_perform() returns as soon as the reads/writes are done. This
function does not require that there actually is any data available for
reading or that data can be written, it can be called just in case. It will
write the number of handles that still transfer data in the second argument's
integer-pointer.
When you call curl_multi_perform() and the amount of running_handles is
changed from the previous call (or is less than the amount of easy handles
you've added to the multi handle), you know that there is one or more
transfers less "running". You can then call curl_multi_info_read(3) to
get information about each individual completed transfer, and that returned
info includes CURLcode and more.
RETURN VALUE
CURLMcode type, general libcurl multi interface error code.
If you receive CURLM_CALL_MULTI_PERFORM, this basically means that you
should call curl_multi_perform 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". Do note that curl_multi_perform(3)
will return CURLM_CALL_MULTI_PERFORM only when it wants to be called
again immediately. When things are fine and there are nothing immediate
it wants done, it'll return CURLM_OK and you need to wait for "action"
and then call this function again.
NOTE that this only returns errors etc regarding the whole multi stack. There
might still have occurred problems on individual transfers even when this
function returns CURLM_OK.
TYPICAL USAGE
Most applications will use curl_multi_fdset(3) to get the multi_handle's
file descriptors, then it'll wait for action on them using select(3) and
as soon as one or more of them are ready, curl_multi_perform(3) gets
called.
SEE ALSO
R curl_multi_cleanup (3), curl_multi_init (3),
R curl_multi_fdset (3), curl_multi_info_read (3),
R libcurl-errors (3)
