curl_multi_perform - reads/writes available data from each easy handle
CURLMcode curl_multi_perform(CURLM *multi_handle, int
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
When running_handles is set to zero (0) on the return of this function,
there is no longer any transfers in progress.
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.
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.
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),