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)