oracular (3) curl_multi_poll.3.gz

NAME

       curl_multi_poll - poll on all easy handles in a multi handle

SYNOPSIS

       #include <curl/curl.h>

       CURLMcode curl_multi_poll(CURLM *multi_handle,
                                 struct curl_waitfd extra_fds[],
                                 unsigned int extra_nfds,
                                 int timeout_ms,
                                 int *numfds);

DESCRIPTION

       curl_multi_poll(3)  polls all file descriptors used by the curl easy handles contained in the given multi
       handle set. It blocks until activity is detected on at least one of the handles or timeout_ms has passed.
       Alternatively,  if  the  multi  handle has a pending internal timeout that has a shorter expiry time than
       timeout_ms, that shorter time is used instead to make sure timeout accuracy is reasonably kept.

       The calling application may pass additional curl_waitfd structures which are similar to poll(2)'s  pollfd
       structure to be waited on in the same call.

       On  completion,  if  numfds  is  non-NULL, it gets populated with the total number of file descriptors on
       which interesting events occurred. This number can include both libcurl internal descriptors as  well  as
       descriptors provided in extra_fds.

       The  curl_multi_wakeup(3)  function  can  be used from another thread to wake up this function and return
       faster. This is one of the details that makes  this  function  different  than  curl_multi_wait(3)  which
       cannot be woken up this way.

       If  no  extra file descriptors are provided and libcurl has no file descriptor to offer to wait for, this
       function instead waits during timeout_ms milliseconds (or shorter if an  internal  timer  indicates  so).
       This is the other detail that makes this function different than curl_multi_wait(3).

       This  function  is  encouraged  to  be  used instead of select(3) when using the multi interface to allow
       applications to easier circumvent the common problem with 1024 maximum file descriptors.

curl_waitfd

       struct curl_waitfd {
         curl_socket_t fd;
         short events;
         short revents;
       };

       CURL_WAIT_POLLIN
              Bit flag to curl_waitfd.events indicating the socket should poll on read events such as  new  data
              received.

       CURL_WAIT_POLLPRI
              Bit flag to curl_waitfd.events indicating the socket should poll on high priority read events such
              as out of band data.

       CURL_WAIT_POLLOUT
              Bit flag to curl_waitfd.events indicating the socket should poll  on  write  events  such  as  the
              socket being clear to write without blocking.

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       int main(void)
       {
         CURL *easy_handle;
         CURLM *multi_handle;
         int still_running = 0;
         int myfd; /* this is our own file descriptor */

         /* add the individual easy handle */
         curl_multi_add_handle(multi_handle, easy_handle);

         do {
           CURLMcode mc;
           int numfds;

           mc = curl_multi_perform(multi_handle, &still_running);

           if(mc == CURLM_OK) {
             struct curl_waitfd myown;
             myown.fd = myfd;
             myown.events = CURL_WAIT_POLLIN; /* wait for input */
             myown.revents = 0; /* clear it */

             /* wait for activity on curl's descriptors or on our own,
                or timeout */
             mc = curl_multi_poll(multi_handle, &myown, 1, 1000, &numfds);

             if(myown.revents) {
               /* did our descriptor receive an event? */
               handle_fd(myfd);
             }
           }

           if(mc != CURLM_OK) {
             fprintf(stderr, "curl_multi failed, code %d.\n", mc);
             break;
           }

         } while(still_running);

         curl_multi_remove_handle(multi_handle, easy_handle);
       }

AVAILABILITY

       Added in curl 7.66.0

RETURN VALUE

       CURLMcode type, general libcurl multi interface error code. See libcurl-errors(3)

SEE ALSO

       curl_multi_fdset(3), curl_multi_perform(3), curl_multi_wait(3), curl_multi_wakeup(3)