curl_multi_wait(3)              libcurl Manual              curl_multi_wait(3)

NAME
       curl_multi_wait - polls on all easy handles in a multi handle

SYNOPSIS
       #include <curl/curl.h>

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

DESCRIPTION
       _multi_wait&section=3">curl_multi_wait(3) polls all file descriptors used by the curl easy
       handles contained in the given multi handle set.  It will block 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 will be 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 will be 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.

       If no extra file descriptors are provided and libcurl has no file
       descriptor to offer to wait for, this function will return immediately.
       (Try curl_multi_poll(3) instead if you rather avoid this behavior.)

       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.

EXAMPLE
       CURL *easy_handle;
       CURLM *multi_handle;

       /* 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 ) {
           /* wait for activity, timeout or "nothing" */
           mc = curl_multi_wait(multi_handle, NULL, 0, 1000, &numfds);
         }

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

         /* 'numfds' being zero means either a timeout or no file descriptors to
            wait for. Try timeout on first occurrence, then assume no file
            descriptors and no file descriptors to wait for means wait for 100
            milliseconds. */

         if(!numfds) {
           repeats++; /* count number of repeated zero numfds */
           if(repeats > 1) {
             WAITMS(100); /* sleep 100 milliseconds */
           }
         }
         else
           repeats = 0;

       } while(still_running);

       curl_multi_remove_handle(multi_handle, easy_handle);

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

AVAILABILITY
       This function was added in libcurl 7.28.0.

SEE ALSO
       curl_multi_fdset(3), curl_multi_perform(3),curl_multi_poll(3) ,

libcurl 7.77.0                 November 5, 2020             curl_multi_wait(3)