CURLMOPT_TIMERFUNCTION

Section: curl_multi_setopt options (3)
Updated: November 04, 2020
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NAME

CURLMOPT_TIMERFUNCTION - set 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 *userp);    /* 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 non-repeating timer with an interval of timeout_ms. When time that timer fires, call either curl_multi_socket_action(3) or curl_multi_perform(3), depending on which interface you use.

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 will only be called when the timeout expire time is changed.

The userp pointer is set with CURLMOPT_TIMERDATA(3).

The timer callback should return 0 on success, and -1 on error. This callback can be used instead of, or in addition to, curl_multi_timeout(3).

WARNING: even if it feels tempting, avoid calling 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

All

EXAMPLE

static gboolean timeout_cb(gpointer user_data)
{
  int running;
  if(user_data) {
    g_free(user_data);
    curl_multi_setopt(curl_handle, CURLMOPT_TIMERDATA, NULL);
  }
  curl_multi_socket_action(multi, CURL_SOCKET_TIMEOUT, 0, &running);
  return G_SOURCE_REMOVE;
}

static int timerfunc(CURLM *multi, long timeout_ms, void *userp)
{
  guint *id = userp;

  if(id)
    g_source_remove(*id);

  /* -1 means we should just delete our timer. */
  if(timeout_ms == -1) {
    g_free(id);
    id = NULL;
  }
  else {
    if(!id)
      id = g_new(guint, 1);
    *id = g_timeout_add(timeout_ms, timeout_cb, id);
  }
  curl_multi_setopt(multi, CURLMOPT_TIMERDATA, id);
  return 0;
}

curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timerfunc);

AVAILABILITY

Added in 7.16.0

RETURN VALUE

Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.