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 - including zero 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 >= 0) {
    /* this is the new single timeout to wait for, including zero */
  }
  else {
    /* delete the timeout, nothing to wait for now */
  }
  return 0;
}

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)