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CURLMOPT_TIMERFUNCTION(3)  Library Functions Manual  CURLMOPT_TIMERFUNCTION(3)


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 CURLcode indicating success or error.

       CURLE_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                           2025-02-08         CURLMOPT_TIMERFUNCTION(3)

curl 8.12.0 - Generated Tue Feb 11 15:27:54 CST 2025
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