NAME

       curl_multi_perform - reads/writes available data from each easy handle

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 an 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)