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. If an
added handle fails very quickly, it may never be counted as a running_handle.
When
running_handles is set to zero (0) on the return of this function,
there is no longer any transfers in progress.
RETURN VALUE¶
CURLMcode type, general libcurl multi interface error code.
Before version 7.20.0: 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 is nothing immediate it wants done, it'll return
CURLM_OK and
you need to wait for "action" and then call this function again.
This function only returns errors etc regarding the whole multi stack. Problems
still might have occurred 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¶
curl_multi_cleanup(3),
curl_multi_init(3),
curl_multi_fdset(3),
curl_multi_info_read(3),
libcurl-errors(3)