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's 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 will store 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 still_running;
       do {
         CURLMcode mc = curl_multi_perform(multi_handle, &still_running);

         if(!mc && still_running)
           /* wait for activity, timeout or "nothing" */
           mc = curl_multi_poll(multi_handle, 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 will 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_cleanup(3), curl_multi_init(3),  curl_multi_wait(3),  curl_multi_add_handle(3),
       curl_multi_fdset(3), curl_multi_info_read(3), libcurl-errors(3)