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() 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.

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  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 available 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_fdset(3),   curl_multi_info_read(3),   libcurl-
       errors(3)

libcurl 7.9.5                                     1 March 2002                             curl_multi_perform(3)