curl/docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.3

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.TH CURLMOPT_TIMERFUNCTION 3 "17 Jun 2014" "libcurl 7.37.0" "curl_multi_setopt options"
.SH NAME
CURLMOPT_TIMERFUNCTION \- set callback to receive timeout values
.SH SYNOPSIS
.nf
#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);
.SH 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 \fBtimer_callback\fP should install a non-repeating
timer with an interval of \fBtimeout_ms\fP. When time that timer fires, call
either \fIcurl_multi_socket_action(3)\fP or \fIcurl_multi_perform(3)\fP,
depending on which interface you use.

A \fBtimeout_ms\fP 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 \fBtimer_callback\fP will only be called when the timeout expire time is
changed.

The \fBuserp\fP pointer is set with \fICURLMOPT_TIMERDATA(3)\fP.

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

\fBWARNING:\fP even if it feels tempting, avoid calling libcurl directly from
within the callback itself when the \fBtimeout_ms\fP value is zero, since it
risks triggering an unpleasant recursive behavior that immediately calls
another call to the callback with a zero timeout...
.SH DEFAULT
NULL
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
.fi
.SH AVAILABILITY
Added in 7.16.0
.SH RETURN VALUE
Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLMOPT_TIMERDATA "(3), " CURLMOPT_SOCKETFUNCTION "(3), "