curl_multi_perform(3)						  libcurl Manual					     curl_multi_perform(3)

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 handles transfers on all the added handles that need attention in an non-blocking fashion.

       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 write 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've 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 very quickly, it may  never
       be counted as a running_handle.

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

EXAMPLE

       #ifdef _WIN32
       #define SHORT_SLEEP Sleep(100)
       #else
       #define SHORT_SLEEP usleep(100000)
       #endif

       fd_set fdread;
       fd_set fdwrite;
       fd_set fdexcep;
       int maxfd = -1;

       long curl_timeo;

       curl_multi_timeout(multi_handle, &curl_timeo);
       if(curl_timeo < 0)
	 curl_timeo = 1000;

       timeout.tv_sec = curl_timeo / 1000;
       timeout.tv_usec = (curl_timeo % 1000) * 1000;

       FD_ZERO(&fdread);
       FD_ZERO(&fdwrite);
       FD_ZERO(&fdexcep);

       /* get file descriptors from the transfers */
       mc = curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);

       if(maxfd == -1) {
	 SHORT_SLEEP;
	 rc = 0;
       }
       else
	 rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);

       switch(rc) {
       case -1:
	 /* select error */
	 break;
       case 0:
       default:
	 /* timeout or readable/writable sockets */
	 curl_multi_perform(multi_handle, &still_running);
	 break;
       }

       /* if there are still transfers, loop! */

RETURN VALUE

       CURLMcode type, general libcurl multi interface error code.

       Before  version	7.20.0:  If  you  receive CURLM_CALL_MULTI_PERFORM, this basically means that you should call curl_multi_perform(3) 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  avail-
       able  to  return  or  that  there  may  be  more  data to send off before it is "satisfied". Do note that curl_multi_perform(3) will return
       CURLM_CALL_MULTI_PERFORM only when it wants to be called again immediately. When things are fine and there is nothing  immediate  it  wants
       done, it'll return CURLM_OK and you need to wait for "action" and then call this function again.

       This  function  only  returns  errors etc regarding the whole multi stack.  Problems still might have occurred on individual transfers 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_fdset(3) to get the multi_handle's file descriptors, and  curl_multi_timeout(3)  to  get  a  suitable
       timeout	period,  then  it'll  wait  for  action  on the file descriptors using select(3). As soon as one or more file descriptor is ready,
       curl_multi_perform(3) gets called.

SEE ALSO

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

libcurl 7.54.0							 February 03, 2016					     curl_multi_perform(3)