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       curl_multi_perform - reads/writes available data from each easy handle


       #include <curl/curl.h>

       CURLMcode       curl_multi_perform(CURLM       *multi_handle,       int


       When the app thinks there’s data available  for  the  multi_handle,  it
       should  call  this  function to read/write whatever there is to read or
       write  right  now.  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.

       When you call curl_multi_perform() and 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

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


       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.


       Most   applications   will   use   curl_multi_fdset(3)   to   get   the
       multi_handle’s file descriptors, then it’ll wait  for  action  on  them
       using  select(3)  and  as  soon  as  one  or  more  of  them are ready,
       curl_multi_perform(3) gets called.


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