Tribblix: manual page: CURLMOPT

CURLMOPT_TIMERFUNCTION(3) Introduction to Library Functions

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 CURLMcode indicating success or error.

CURLM_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).