docs/libcurl/opts/CURLMOPT_TIMERFUNCTION.3

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.TH CURLMOPT_TIMERFUNCTION 3 "May 27, 2017" "libcurl 7.61.1" "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, /* see above */
                   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. Each 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 means you should delete your timer.

A \fBtimeout_ms\fP value of 0 means you should call
\fIcurl_multi_socket_action(3)\fP or \fIcurl_multi_perform(3)\fP (once) as soon
as possible.

\fBtimer_callback\fP will only be called when the \fBtimeout_ms\fP changes.

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.
.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), "