curl_multi_perform – reads/writes available data from each easy handle

USAGE
       #include 

       CURLMcode  curl_multi_perform(CURLM  *multi_handle,  int  *running_han-
       dles);

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 actu-
       ally 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.

RETURN VALUE
       CURLMcode type, general libcurl multi interface error code.

       If you receive CURLM_CALL_MULTI_PERFORM, this basicly  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".

       NOTE that this only returns errors etc regarding the whole multi stack.
       There  might  still  have  occurred problems on invidual transfers even
       when this function returns OK.

TYPICAL USAGE
       Most application will use curl_multi_fdset to  get  the  multi_handle’s
       file descriptors, then it’ll wait for action on them using select() and
       as soon as one or more  of  them  are  ready,  curl_multi_perform  gets
       called.