NAME

       CURLMOPT_TIMERFUNCTION - callback to receive timeout values

SYNOPSIS

       #include <curl/curl.h>

       int timer_callback(CURLM *multi,    /* multi handle */
                          long timeout_ms, /* timeout in number of ms */
                          void *clientp);  /* private callback pointer */

       CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_TIMERFUNCTION, timer_callback);

DESCRIPTION

       Pass a pointer to your callback function, which should match the prototype shown above.

       Certain  features,  such  as  timeouts  and  retries,  require  you to call libcurl even when there is no
       activity on the file descriptors.

       Your callback function timer_callback should install a single non-repeating timer with an expire time  of
       timeout_ms   milliseconds.   When   that   timer   fires,   call  either  curl_multi_socket_action(3)  or
       curl_multi_perform(3), depending on which interface you use.

       If this callback is called when a timer is already running, this new  expire  time  replaces  the  former
       timeout.  The application should then effectively cancel the old timeout and set a new timeout using this
       new expire time.

       A timeout_ms value of -1 passed to this callback means you should delete the timer. All other values  are
       valid expire times in number of milliseconds.

       The timer_callback is called when the timeout expire time is changed.

       The clientp pointer is set with CURLMOPT_TIMERDATA(3).

       The  timer  callback  should  return  0  on success, and -1 on error. If this callback returns error, all
       transfers currently in progress in this multi handle are aborted and made to fail.

       This callback can be used instead of, or in addition to, curl_multi_timeout(3).

       WARNING: do not call libcurl directly from within the callback itself when the timeout_ms value is  zero,
       since  it  risks  triggering  an unpleasant recursive behavior that immediately calls another call to the
       callback with a zero timeout...

DEFAULT

       NULL

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       struct priv {
         void *custom;
       };

       static int timerfunc(CURLM *multi, long timeout_ms, void *clientp)
       {
         struct priv *mydata = clientp;
         printf("our ptr: %p\n", mydata->custom);

         if(timeout_ms) {
           /* this is the new single timeout to wait for */
         }
         else {
           /* delete the timeout, nothing to wait for now */
         }
       }

       int main(void)
       {
         struct priv mydata;
         CURLM *multi = curl_multi_init();
         curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timerfunc);
         curl_multi_setopt(multi, CURLMOPT_TIMERDATA, &mydata);
       }

AVAILABILITY

       Added in curl 7.16.0

RETURN VALUE

       curl_multi_setopt(3) returns a CURLMcode indicating success or error.

       CURLM_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO

       CURLMOPT_SOCKETFUNCTION(3), CURLMOPT_TIMERDATA(3)

libcurl                                            2025-03-05                          CURLMOPT_TIMERFUNCTION(3)