NAME

       curl_multi_perform - reads/writes available data from easy handles

SYNOPSIS

       #include <curl/curl.h>

       CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);

DESCRIPTION

       This  function  performs  transfers on all the added handles that need attention in a non-
       blocking fashion. The easy handles have previously been added to  the  multi  handle  with
       curl_multi_add_handle(3).

       When  an  application  has  found  out  there  is data available for the multi_handle or a
       timeout has elapsed, the application should call  this  function  to  read/write  whatever
       there  is  to  read  or write right now etc.  curl_multi_perform(3) 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
       stores the number of handles that still transfer data in the  second  argument's  integer-
       pointer.

       If  the  amount  of running_handles is changed from the previous call (or is less than the
       amount of easy handles you have 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  quickly,  it may never be counted as a
       running_handle. You could use curl_multi_info_read(3) to track actual status of the  added
       handles in that case.

       When running_handles is set to zero (0) on the return of this function, there is no longer
       any transfers in progress.

       When this function returns error, the state of all transfers are uncertain and they cannot
       be  continued.  curl_multi_perform(3)  should not be called again on the same multi handle
       after an error has been returned, unless first removing all the  handles  and  adding  new
       ones.

EXAMPLE

       int main(void)
       {
         int still_running;
         CURL *multi = curl_multi_init();
         CURL *curl = curl_easy_init();
         if(curl) {
           curl_multi_add_handle(multi, curl);
           do {
             CURLMcode mc = curl_multi_perform(multi, &still_running);

             if(!mc && still_running)
               /* wait for activity, timeout or "nothing" */
               mc = curl_multi_poll(multi, NULL, 0, 1000, NULL);

             if(mc) {
               fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc);
               break;
             }

           /* if there are still transfers, loop! */
           } while(still_running);
         }
       }

AVAILABILITY

       Added in 7.9.6

RETURN VALUE

       CURLMcode type, general libcurl multi interface error code.

       This  function  returns  errors  regarding  the  whole multi stack. Problems on individual
       transfers  may  have  occurred   even   when   this   function   returns   CURLM_OK.   Use
       curl_multi_info_read(3) to figure out how individual transfers did.

TYPICAL USAGE

       Most  applications  use curl_multi_poll(3) to make libcurl wait for activity on any of the
       ongoing transfers. As soon as one or more file descriptor has  activity  or  the  function
       times out, the application calls curl_multi_perform(3).

SEE ALSO

       curl_multi_add_handle(3),            curl_multi_cleanup(3),           curl_multi_fdset(3),
       curl_multi_info_read(3), curl_multi_init(3), curl_multi_wait(3), libcurl-errors(3)