focal (3) curl_multi_wait.3.gz

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

       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) ,